FRESHWATER FISH POND
CULTURE AND MANAGEMENT
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VOLUNTEERS IN TECHNICAL ASSISTANCE
1600 WILSON BOULEVARD, SUITE 500
ARLINGTON, VIRGINIA 22209, USA
APPROPRIATE TECHNOLOGIES FOR DEVELOPMENT
FRESHWATER FISH POND
CULTURE AND MANAGEMENT
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FRESHWATER FISH POND
CULTURE AND MANAGEMENT
[C] VITA, 1976
May be reproduced without
payment of royalty for official
U.S. Government purposes.
About this manual....
Freshwater Fish Pond Culture and Management is the second in
a series
of publications being prepared by the United States Peace
Corps and
VITA, Volunteers in Technical Assistance.
These publications combine
Peace Corps' practical field experiences with VITA's
technical expertise
in areas in which development workers have special
difficulties finding
useful resource materials.
PEACE CORPS
Since 1961 Peace Corps Volunteers have worked at the grass
roots level
in countries around the world in program areas such as
agriculture,
public health, and education.
Before beginning their two-year assignments,
Volunteers are given training in cross-cultural, technical,
and language skills.
This training helps them to live and work closely
with the people of their host countries.
It helps them, too, to
approach development problems with new ideas that make use
of locally
available resources and are appropriate to the local
cultures.
Recently Peace Corps established an Information Collection
& Exchange
so that these ideas developed during service in the field
could be made
available to the wide range of development workers who might
find them
useful. Materials
from the field are now being collected, reviewed,
and classified in the Information Collection & Exchange
system. The
most useful materials will be shared.
The Information Collection &
Exchange provides an important source of field-based
research materials
for the production of how-to manuals such as Freshwater Fish
Pond Culture
and Management.
VITA
VITA people are also Volunteers Who respond to requests for
technical
assistance. In
providing solutions, their aim is the most appropriate
answers for specific situations.
Therefore, VITA specialists often must
produce new designs or adapt technologies so that they are
of value
in developing areas.
Many VITA Volunteers have lived and worked abroad.
Most VITA people now
work in the United States and other developed countries
where they are
engineers, doctors, scientists, farmers, architects,
writers, artists,
and so on. But they
continue to work with people in other countries
through VITA. Thanks
to their contributions of time and expertise, VITA
has been providing technical assistance to the Third World
for more than
15 years.
Requests for technical assistance come to VITA from many
nations. Each
request is sent to a Volunteer with the right skills.
For example, a
question about fish pond operation might be sent to a VITA
Volunteer who
has had years of experience working to develop fish ponds in
Asia, and
who is now a university professor.
THE PURPOSE
Freshwater Fish Pond Culture and Management is a how-to
manual. It is
designed as a working and teaching tool for extension
agents. It is for
their use as they establish and/or maintain local fish pond
operations.
The information is presented here to 1)
facilitate technology transfer
and 2) provide a
clear guide for warm water fish pond construction and
management. A
valuable listing of resources at the end of this manual
will give further direction to those wishing more
information on various
aspects of fish pond operation.
THE PEOPLE WHO PREPARED IT
The strength of both Peace Corps and VITA lies in
Volunteers. These
manuals represent an excellent means of communicating
important know-how
gained through Volunteer experiences and inputs.
The author of Freshwater Fish Pond Culture and Management,
Marilyn
Chakroff, served with Peace Corps in the Philippines for
three years
in a number of fisheries programs.
Ms. Chakroff, who holds a B.S. in
Biology, now is an advanced degree candidate in the field of
Environmental
Communications at the State University of New York, in
Syracuse.
This manual is written out of her first-hand experience as a
Peace
Corps Volunteer.
Joan Koster, the illustrator, has been a VITA Volunteer for
more than 3
years. She is a
teacher, professional artist, and writer.
Ms. Koster,
who has travelled and studied in Greece for a number of
years, currently
is preparing a manuscript on looms and weaving.
OTHER CONTRIBUTORS
Many thanks are due here to a number of people who aided the
preparation
of this manual:
Dr. David Hanselman, Dr. Peter Black, and Dr. Robert Werner
-- Faculty
of the College of Environmental Science and Forestry, State
University of
New York, Syracuse, New York.
Dr. Shirley Crawford, Agricultural and Technical College,
State University
of New York, Morrisville, New York.
William McLarney, New Alchemy Institute, Woods Hole,
Massachusetts.
A.F. D'Mello, Hawkesbury Agricultural College, New South
Wales,
Australia.
Richard T. Carruthers, Bioproducts, Inc., Warrenton, Oregon.
Dr. William Ribelin, Department of Veterinary Science,
University
of Wisconsin, Madison.
A special note of thanks is due John Goodell, VITA, for his
layout work
and staff assistance with this manual.
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1. How did you find
out about the PC/VITA Freshwater Fish Pond Culture
and Management
manual? How did you get your copy?
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Least useful?
Why?
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the information?
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when you were building a drainage system, did you
substitute any
materials for the ones mentioned or change the design?)
If you made
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Include photos,
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Table of Contents
Section
"About This Manual"
Reply
Form
1
INTRODUCTION
2
PLANNING:
THE SITE AND THE TYPE OF FISH FARM
3
PLANNING:
SELECTION OF FISH
4
FISH POND CONSTRUCTION
5
PREPARING THE POND
6
MANAGING THE POND
7
HARVESTING THE POND
8
PRESERVING FISH
9
PROBLEMS OF FISH IN PONDS
10
OTHER METHODS OF FISH CULTURE
Glossary
Resources
Measurements Used in This Manual
Index
1
Introduction
What is Fish Culture?
Fish culture is the growing of fish in ponds.
Growing fish in ponds,
from which they cannot escape, allows feeding, breeding,
growing, and
harvesting the fish in a well-planned way.
Fish culture is one form of aquaculture.
Aquaculture is the science
which deals with methods of growing (cultivating) animal and
vegetable
life in water. Some
other kinds of aquaculture are concerned with growing
frogs, oysters, seaweed, and even rice.
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History of Fish Culture in Ponds
Growing fish in ponds is a very old practice.
Carp were cultured as long
ago as 2698 B.C. in China, where they were grown in ponds on
silkworm
farms. Fish culture
seemed to occur whenever civilization was settled
for a long period of time.
For example, fish culture was done in ancient
Egypt and in China, which has had a continuous civilization
for over
4,000 years. The
first written account of fish culture in ponds was by
Fan Lai, a Chinese fish farmer, in 475 B.C.
The ancient Romans introduced carp from Asia into Greece and
Italy. By
the seventeenth century (1600's), carp culture was being
done all over
Europe. A book
written in England in 1600 by John Taverner gives the
details of good pond management and talks about growing the
common carp.
Taverner also wrote about pond construction, fertilization
and feeding.
Another book, written in 1865, gave the details of the
stripping methods
of spawning fish.
The methods of culturing common carp have not changed
very much since that time.
The common carp is still a very important pond fish.
In addition,
today, other fish also are being cultured in ponds.
Some of the most
well-known are fish of the tilapia genus, like Tilapia
nilotica and
Tilapia mossambica.
Some of the other Chinese carps -- the silver, grass,
and bighead carps -- also are often used in pond
culture. Most importantly,
countries all over the world are using time and money to
discover which
of the fish commonly found in their own waters will grow
well in fish
ponds.
Why Fish are Grown in Ponds
The practice of culturing fish in ponds developed because growing
fish in
ponds is a more useful practice, for some purposes, than
trying to catch
fish from lakes, rivers, or streams.
For example:
*
Many interested people discover that
building a fish pond
close to home
is possible and far more convenient than going
to the nearest
market or river. Ponds can be built
wherever
the soil, shape
of the land, and water supply are right.
This
may sound as if
a lot of factors are involved. But
since a
wide variety of
soils, land shapes, and water supplies can be
used for pond
culture, a fish pond can even be made from a
rice paddy or
an unused grain field.
*
It is easier to get fish out of a pond than
it is to catch a
fish from a
river or stream. Also, the number of
fish taken
out of a pond
can be controlled. But it is very
difficult to
know how many
fish can be caught in a river or stream or lake
at any one
time. When the farmer goes to his fish
pond to get
dinner, he
knows he can take out the number of fish he needs
-- quickly and
easily.
*
Fish growth can be controlled.
The fish can be fed extra
food to make
them better for market; natural enemies can
be kept from
killing the fish. For a person who
relies on
fish for his
food or his income, these are important factors.
*
The only fish grown in a pond are the ones
the farmer
wants to
grow. When he takes a fish out of his
pond, the
farmer knows
what kind or kinds he will be getting.
When
he catches fish
in a lake,
stream, or
river, many of the
fish will not
be the ones that
are good to eat
or to sell.
*
Growing fish in ponds allows
the farmer, or
other fish
grower, to
produce fish
cheaply, and to
have a supply
of fish
available on his own
land.
Fish in ponds belong
to the pond
owners; fish in
the rivers and
lakes do not.
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Why Growing Fish is Important
There are some very good reasons why a farmer or small land
owner might
be interested in fish farming:
*
Fish are an important food source.
*
Fish farming can help a farmer make the best
use of his land.
*
Fish farming can provide extra income.
There may be additional reasons; you and the pond owners can
determine
these from the local situation.
The three points listed above are very
broad, however, and apply, at least in part, to most
situations.
Therefore, each point is discussed more fully below.
FISH AS FOOD Farmers
know that all living things need food, and that
without food, living things die.
However, they are not as likely to know
the characteristics of food which make it valuable (or not)
to the body.
Food is important because it provides proteins, vitamins,
minerals, fats,
and carbohydrates.
These things are called nutrients:
they are materials
that the body must have to live and grow.
Every kind of food has different
amounts of each of these nutrients.
For example, some foods
contain more protein; others have more fat than protein.
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Because foods contain different amounts
of proteins, fats, and carbohydrates,
for example, it is necessary to eat a
number of different kinds of food to
get the right amounts of each nutrient.
All the foods together then give the
body what it needs to grow.
The food that people eat is called
their diet. Eating
the right kinds of
food -- foods that give the body the
right amounts of proteins, fats, etc.
-- is called eating a balanced diet.
People who eat a balanced diet usually
are healthy and strong; people who do
not eat the right kinds of food are
more likely to be weak and get sick.
Proteins are the most important part of food.
Protein is made of carbon,
hydrogen, and nitrogen.
These are called elements. The
combinations of
elements in protein make it the most useful nutrient.
Foods that contain
a lot of protein are especially good for people to eat.
And fish contains
a lot of protein.
The table on the opposite page shows a list of foods that
humans eat.
The first number beside the food shows the number of grams
of protein in
the food when it is fresh.
The second number tells how many grams of
protein there are in food which has been dried.
The table shows that
fish -- whether fresh or dried -- is a very good source of
protein.
(100gm of dried fish contains more protein than 100gm of
fresh fish only
because dried foods have water taken out.
Therefore, 100gm of fresh fish
weighs less when it is dried.)
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If the farmers in your area already eat a lot of fish, or
like fish, fish
farming for food may not be hard to introduce and have
accepted.
If they do not eat fish often, you will have to keep this in
mind when
you talk about fish as a healthy food.
Food just may not be the most
important reason, from their point of view, for wanting to
grow fish.
PROTEIN
CONTENT OF FOODS (*)
Fresh, gms protein
Dried, gms protein
Food
per 100gm
per 100gm
FISH
Fatty (herring)
17
46
Non-fatty (haddock)
16
84
MEAT
Beef
20
67
Pork, loin
20
67
Liver
20
67
DAIRY PRODUCTS
Milk
3.4
26
Eggs
12
46
CEREALS
Wheat
12
14
Maize
10
11
Oats
10
11
Rice
8
9
OIL SEEDS
Soya
33
37
Cottonseed
20
21
Sesame
21
22
GREEN LEAFY VEGETABLES
Cabbage
1.4 - 3.3
24
Spinach
2.3 - 5.5
26
ROOTS
Cassava (manioc )
0.7
2
Potatoes
2.1
9
Yams
2.1
7
Plantains
1.0
3
(*) These
values are estimates only; the amount
of
protein varies according to the age, size,
and
quality of the food, and how it was
cooked
and stored.
Source: Aylward and
Jul (1975)
But there are other reasons you can offer a farmer.
For example, a
farmer may consider cultivating fish if he realizes that
fish are easy
to grow, cheaper than some kinds of meat, available as food
all year
round, etc. You will
have to see which combination of arguments works
best for getting farmers interested.
BETTER LAND USE Some
farmers may be more interested in fish farming
when they realize they can accomplish two purposes:
provide a reliable
food supply and make the best possible use of their land.
"Fish farming" is a good thing to call "fish
culture" because it can
start the farmer thinking about raising fish with the same
kind of planning
and land-use management ideas that he puts into raising
crops.
Whether the farmer raises fish, crops, or animals, he is
using his land
in certain ways. His
aim in all cases is to increase the production of
food and the yield from the land.
What farmers, and other people, often
do not realize is that fish culture can help get more out of
the land.
Here are a few ways in which fish culture can help support
and extend a
farmer's land use:
*
Land gets tired when it is used for growing
the same crop
year after
year. These crops use up nutrients in
soil, and
they begin to
grow poorly. Fish ponds can be built on
this
land and
fertilized to provide food for the fish.
After a
few years of
fertilizing and growing fish, the soil inside
the pond
regains some of the nutrients used up by the growing
of crops year
after year. The land can then be used
for
crops again.
*
Some farmers own land that may not be very
good for growing
crops:
it is too sandy, for example.
But there are ways of
building fish
ponds in sandy soil. So the farmer
would be
able to use
land that was once not of much value to him.
*
There are many ways that fish farming can
fit into the
farmer's plan
for his land. The important thing is
that all
of these ways
help the farmer make the best use and get more
out of what he
has -- readily, and often without much expense.
For example, a
farmer who grows paddy rice can grow fish in
that paddy;
fish ponds can be built as part of water supply
and irrigation
systems; vegetable scraps and animal manures
can be
collected and used for fertilizing ponds.
The farmer
should know
that a farm with a fish pond or ponds can give
a total food
yield that is higher than a farm with no fish
ponds.
The following diagram illustrates some of the ways in which
the fish
pond fits into the farm:
The same water source is used by both the
garden and the fish pond; the mud from the bottom of the
pond makes
good fertilizer for the garden; vegetable matter from the
garden can be
used to fertilize fish ponds; manure from the animals can be
used for the
pond and parts of fish can be used to feed animals; etc.
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ADDED INCOME Fish
ponds can be quite small, or they can be large.
They can be made using expensive equipment and drainage
systems, or they
can be dug using hand tools and drained by a bamboo
pipe. Fish can grow
successfully in both of these types of pond, as long as the
ponds are
managed correctly.
If the major reason for building the fish pond is to get
increased and
better food for his family, a farmer certainly does not need
fancy ponds
or expensive equipment.
Fish ponds can be very inexpensive to keep.
Fish do not require fancy foods.
Many ponds provide all the food the
fish need. But
besides the foods they find in water itself, some fish
eat leafy garbage, mill sweepings, beer residues, spoiled
grains, broken
rice, and many other waste products that might not otherwise
be used.
A farmer makes his income go further by growing more of the
family's
food and by selling leftover fish the family cannot eat.
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Growing fish to sell can also be
very profitable. But
the costs
involved in getting started and in
maintaining the effort are greater:
if the farming is to be a solid
commercial enterprise, then more
ponds, more time, more money, and
nearby marketplaces are needed.
The business may or may not show
a profit right away; in fact, the
chances are that it will not.
A
farmer might be better advised to
start small and work into a bigger
enterprise slowly as he learns to
manage the art of growing fish in
ponds.
A Word about Cooperation
Often fish ponds are built by cooperatives.
A cooperative is an organization
of people in an area who come together to do something they
could
not or would not do alone.
In this way, four or five people or families
can pool their resources and build a fish pond operation
together.
Sometimes an entire village will form a cooperative and will
build and
operate a pond as a group.
This kind of cooperation makes possible
better pond construction and management.
A fish pond cooperative may be
a good way for a village to improve the diet of the community
and to sell
enough fish to maintain the enterprise.
If the farmers in your area are
not interested in, or are concerned about, building ponds
individually,
a cooperative may be a very acceptable idea.
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Getting Ready to Plan a Fish Farm
A farmer or other person interested in growing fish should
read the
following list carefully before going further.
The following factors
must be considered before the farmer builds his fish
pond. Many pond
owners have small fish ponds that are only used for their
own families,
but a farmer who sells fish must look for a market and a way
to get his
fish to that market.
It does no good to harvest fish which cannot be
sold or used by the farmer and his family.
*
Is the soil able to hold water for a fish
pond?
*
Is there an adequate supply of water for a
pond?
*
Is the land a good shape for a fish pond?
*
Is the pond area close to your home?
*
Who owns the land where the pond will be
built?
*
Are there enough people to help build and
harvest the pond?
*
Can the equipment for building a pond be
built, borrowed, or bought.
*
Is there a marketplace nearby?
*
Are there roads from the pond area to a
market place?
*
Are the roads passable even in the rainy
season?
*
Is there a good way to get the fish to
market?
*
Is there a vehicle available for
transportation, if necessary?
*
If there is no market nearby, or if it is
hard to get to the
market, can the
fish be kept by drying, smoking, or salting?
*
Is there enough food for the pond fish?
*
Are there fertilizers available?
*
Do the people in the area like fish?
Do they eat freshwater fish?
*
Can the people in the area afford to buy the
fish produced in the
pond?
If the farmer can answer yes to the questions which most fit
his
situation, he has a good chance of having a successful fish
pond.
But he must consider these factors.
Each is discussed in detail in
the "Planning" sections.
2 Planning:
The Site and the
Type of
Fish Farm
Before construction can begin, the farmer must look over his
land to
choose the place or places where ponds can be built, and
decide what
kind and how many to build.
He must also decide on the kind of fish
culture he wants to do, and on the type of fish that he
wants to raise.
He must look at his resources and his needs very carefully
before he
actually begins building and operating a fish pond.
This section will
give information to guide the farmer in the planning of
ponds and kind
of fish culture.
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The Site
One of the most important parts of planning is finding the
right place
(selecting the site) for the pond.
Fish ponds use the land in a different
way from agricultural crops such as rice or wheat, but fish
also are a
crop. And when a
farmer builds a fish pond, he is choosing one use of
his land instead of some other use.
If the site for the pond is well-chosen,
the pond can be more productive than the land by
itself. But if
it is not chosen well, the farmer may lose, or, at best,
gain nothing
from his fish pond.
When considering a site for the fish pond, the
farmer should remember and consider several points that were
made in the
introduction:
*
Often poor agricultural land can be turned
into very good fish
ponds.
In general, the better the soil of an area,
the better
the fish
pond. But this does not mean that a
pond cannot be
built on
poor land.
It does mean that the farmer will have to
work harder to
maintain the pond and the fish.
*
If the pond is built on agricultural land
which is not producing
good crops, but
the pond is cared for well, eventually the pond
bottom soil
will become more fertile than it was before.
If
this pond is a
large one, after harvesting the fish, the pond
can be planted
again with a land crop, like corn, and allowed
to grow.
Then when the corn is harvested, the land
can be
turned back
into a fish pond. This means that a
farmer can get
two good uses
out of his land instead of one poor crop.
*
Other farmers may want to grow fish in rice
paddies by digging
trenches around
the edges of the paddy for fish to swim in.
This is another
way of culturing fish which will be discussed
in somewhat
more detail later in the manual.
The point of the discussion above, is that a fish pond is
just one use
that a farmer's fields can have, and the choice of how the
land can be
used is important.
<FIGURE>
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There are three factors that work together to make a good
site for a
fish pond:
*
Water supply
*
Soil
*
Topography
WATER SUPPLY Water
supply, soil, and topography all are important,
but water supply is the most important factor in selecting a
site. Fish
depend upon water for all their needs:
fish need water in which to
breathe, to eat, and to grow and reproduce.
If a site has water available
year-round, that site meets its first test easily.
If water is not
available all the time but there is some way to store water
-- in large
tanks, barrels or drums, in depressions, ponds, or wells --
for use when
the natural water supply is low, then that site may still be
all right.
The key, of course, is that water must be available at all
times and in
good supply.
Where Can Water for Fish Ponds Come From?
Water used in ponds comes
from many sources:
*
Rainfall.
Some ponds, called "sky" ponds, rely only on rainfall
to fill their
need for water.
*
Run-off.
Some ponds are gravel and sand pits which fill when
water from the
surrounding land area runs into them.
*
Natural waters.
Most ponds are filled with water that comes
from natural
springs or wells, or with water that has been
channelled
(diverted) and brought in from streams, rivers,
or lakes.
*
Springs.
Some ponds are built where there is a spring to supply
water.
Spring water is water under the ground that
has found a
way to get
out. It leaves the ground and becomes a
stream as it
flows away.
Spring water is good for fish ponds because it is
usually clean
(uncontaminated) and has no unwanted fish or fish
eggs in
it. If the water from a spring has
travelled very far,
it may need to
be filtered before it is used for a fish pond.
But filtering
is easy to do (see the "Construction" section)
and the
important fact is that the water supply is available.
<FIGURE>
12p13.gif (426x528)
*
Wells.
The best source of water for a fish pond is well water.
Well water has
few contaminants and, if the well is a good one,
the water is
continuously available. Well water and
spring
water, however,
are both often low in oxygen content.
Fish
need to have
oxygen in their water to live. Since
this problem
is overcome easily (see water quality
information in the section
on
"Preparing the Pond") the major factor to be considered
here is an
adequate water supply.
Most fish ponds use water that comes from a stream, river,
or lake.
A diversion ditch or channel is dug between the water source
and the
pond to take water from source to pond.
This is a good way to fill a
pond because the water can be controlled easily.
When the pond is full,
the channel can be blocked with a gate or a plug (see
"Construction"
section), and the water will stop moving into the pond.
There can be problems with this kind of water supply; for
example, often
in tropical areas streams flood in the rainy season.
This extra water
can be dangerous to the pond and must be diverted away from
the pond by
a channel built for that purpose.
IT IS BEST NOT TO CHOOSE A PLACE THAT
IS KNOWN TO FLOOD WHEN CHOOSING A WATER SUPPLY AND SITE FOR
A POND. When
a pond floods, all the fish escape, and the pond is empty at
harvest time.
If the water for the pond is being taken from a stream,
lake, or river,
then the farmer should plan to filter the water carefully
when filling
the pond. Water from
these sources sometimes contains unwanted fish or
fish eggs. Filtering
prevents these fish or eggs, and other harmful
animals, from entering the pond.
Quality of the Water Supply.
Finding an adequate water supply is the
first step. Then the
farmer has to check that supply to make sure it
can be used for a pond.
This check of the water should include:
*
looking at the water, smelling it and
tasting it.
*
looking to see if there is a family upstream
who take baths in
the water
before it gets to the pond.
*
making sure that there is no family or
village downstream that
depends upon the source for their
drinking water.
If the water supply seems all right, the farmer must also
find the
answers to some other questions.
Where the water comes from, how far it
travels to get to the site for the pond, and what kind of soil
it travels
over will all affect the quality of the water.
These questions and their
answers tell what must be done to make the water right for a
pond:
*
Is the water very clear?
Then the farmer may have to fertilize
the pond
because there are not enough nutrients in the water.
*
Is the water very muddy?
Then it will have to settle before it
is used in the
pond: a special place will have to be
made
where the mud
can settle out of the water before the water
goes into the
pond.
*
Is the water a bright green?
It probably has a lot of fish
food in it.
*
Is the water a dark, smelly brown?
It may have acid in it,
and the farmer
will have to add lime to the water.
There are many things which can be done to make water good
for a pond.
If the farmer knows his supply and the kind of water he has,
he can
take the steps necessary to use his supply well.
SOIL The second
important part of site selection is the soil of the
area. The soil of
the pond must be able to hold water. It
also contributes
to the fertility of the water because of the nutrients it
contains.
Ability of Soil to Hold Water.
The best soil for a pond contains a lot
of clay. Clay soil
holds water well. When a place with a
good water
supply is found, the farmer must test the soil.
He can tell a lot about
the soil simply by feeling it.
If the soil feels gritty or rough to the
touch, it probably contains a lot of sand.
If it feels smooth and
slippery, it probably means there is a lot of clay in
it. This smooth
soil is good for a fish pond.
A very good way
to tell if the soil is right for a fish
pond is to wet
a handful of soil with just enough water
to make it
damp.
<FIGURE>
12p15.gif (256x256)
Then squeeze
the soil.
<FIGURE>
12p16a.gif (230x230)
If it holds its
shape when the farmer opens his hand, it will
be good for a
pond. Remember, the more clay in the
soil, the
better it is
for building a pond.
<FIGURE>
12p16b.gif (230x230)
If the soil is sandy, or does not contain much clay, the
farmer can still
build a pond. There
are ways of building ponds in these soils.
But he
should be aware that building a fish pond in such soils
requires more
effort and may not be as successful.
Digging test holes will tell the
farmer what his soil is.
Larger ponds can be built in soils with clay.
If the soil is rocky or has
shifting sand, etc., only small ponds are possible.
If there are other
locations available, the farmer would be wise to see if
there is another
place with soil better suited to the fish pond.
More information on soil
is included in the "Construction" section.
Ability of Soil to Provide Nutrients.
Soil also contributes to the pond's
fertility. Fertility
is a measure of the nutrients in the pond, and it
simply refers to how much food there is available in the
pond for the
fish to eat. A very
fertile pond is one which contains a lot of fish food.
The soil of the pond contains some of these necessary
nutrients -- like
iron, calcium, and magnesium.
In addition, however, soil also can contain
acids; these substances often are harmful to fish.
Whatever a soil has
in it is drawn into the pond by the water and thus comes in
contact with
the fish. Sometimes
after a heavy rainstorm, there are big fish kills
in new ponds. This
happens because the heavy rain carries larger
amounts of acids from the soil into the pond.
So the farmer who is aware
of the kind of soil he has for his fish pond can prevent
this problem
before it happens.
REMEMBER: One good
indicator of the quality of soil is whether it has
been used for growing crops.
If crops grow well in that location, the
soil will probably be good for the fish pond.
If crops did grow well
there before the nutrients were used up, then it will
probably still be
free of harmful substances.
TOPOGRAPHY The third
factor in site selection is topography.
Topography is a word used to describe the shape of the land
-- whether
it is flat or hilly, upland or lowland, etc.
The topography of the land
determines the kinds of ponds which can be built.
Ponds can be built in
valleys or on flat ground.
They can be square or rectangular, or uneven
in shape. They can
be large or small. All of this is
determined by
topography of the land, as well as by the farmer's
requirements.
The most useful topography for fish ponds is that which
allows the farmer
to fill and drain ponds using gravity.
Ponds built on a slope, for
example, can be drained easily.
If ponds are located on flat land, the
pond must be built with a slope inside it so it can be drained
by gravity,
or it will have to be drained using a pump.
Slope. If the farmer
looks at a hillside, he can see that it rises.
It
is higher at one point than at another.
This difference in height, from
high to low point, is the slope of the land.
In more scientific terms,
slope is the relationship between the horizontal distance
(length) and
the vertical distance (elevation) over a piece of land.
Slope is usually written as a ratio (1:2) or as a percentage
(5%). A
slope of 1:2 means that for every change in length of 2
meters, there is
a change of 1 meter in height.
A slope of 5% means that for every change
in length of, say, 100cm, there is a change in height of
5cm. Pond
bottoms usually have a slope of 2-5%, whether they are on
level ground
or in a hilly area.
As long as the pond bottom has a slope, it can be
drained completely.
A farmer does not require a scientific understanding of
slope to build
a pond. He does need
to know how the shape of his land determines the
best place for building ponds.
Ponds built in hilly places often are
made part of the hill.
The picture on top of the next page, of a pond
with a spring as a water source, shows how the slope of the
land has
been used to set up the pond's drainage system.
<FIGURE>
12p18.gif (437x437)
In flatter areas, ponds are usually square or rectangular
because it is
easier to use a harvesting net in ponds of these shapes.
The farmer will learn quickly to recognize by sight the
slope that is
best for a pond.
Because a slope is so important, the first thing a
farmer should look for is a site with a slope and a water
supply. If
he can use a natural slope for his pond, the pond will be
cheaper and
easier to construct.
The best places to look for such combinations of slope and
water supply
are where water collects from streams and flows through the
valley at
the bottom of a slope.
If the pond is built on the slope above the
water flow, water drained from the pond can flow directly
into the stream.
Water might be brought to the pond in a number of ways depending
upon the
situation -- by streams running down the slope upon which
the pond is
situated, for example.
Another good place to look for a good combination
of slope and water supply is on plains or flattish ground
between hills.
These plains often receive water from brooks or streams.
There are many possibilities.
The important thing is that the farmer
look for a topography that makes fish farming as easy and as
successful
as possible.
The Type of Fish Farm
After the farmer has found a site or sites for his fish
pond, he must
consider what kinds of fish culture are possible in the
space he has
available. He also
must decide what his resources will allow him to
get started. This
planning is necessary because the answers will
determine the number of fish ponds the farmer builds and the
kind of
fish he will want to culture.
The following pages present a range of
ideas concerning the kinds of fish farm operations (raising
fish or
breeding fish); the types of pond used in fish culture; fish
culture in
one or several ponds; advantages of small and large ponds;
and mixing
or separating fish types and sexes.
A discussion of these subjects will
provide the farmer with the background he needs to decide
what kind of
fish farm is possible for him, given his resources and the
kind of fish he
wants to raise.
A NOTE OF CAUTION
Before a farmer even begins, however, it is important
for him to include in his planning the fact that some fish
will die.
This is an extremely important fact for the first-time fish
grower to
understand. It is
very natural for some fish, the weaker fish, to die in
ponds. As long as
fish are protected in ponds and are well taken care of,
fewer fish will die in ponds than would die in natural
waters. But a
farmer who does not expect some death may get discouraged
and give up
before he has given his pond a chance to work.
It is never too early to
introduce this idea.
KINDS OF FISH FARM OPERATION
In nature, many fish never reach
adult size because they are eaten by other animals (predators),
or they
die from disease or lack of oxygen.
In fish culture, the farmer tries
to control the pond situation in order to produce more
fish. In ponds,
predators and so on can be controlled so that the pond
yields more fish
per hectare than do natural waters.
There are two major kinds of fish farms -- those which breed
fish and
raise the fry, and those which rear fry and fingerlings (the
young fish)
to market size. So
the farmer, after finding possible sites, etc., must
decide if he is going to breed his fish and raise the
fry. Or if he is
going to buy fry and fingerlings and rear them to market
size, not
getting involved in breeding.
Breeding fish requires more time and more ponds than simply
rearing
fingerlings. And
building more ponds can be more expensive and require
more ongoing management.
So the farmer must finally determine his reason
for raising fish: to
eat; to sell; to use his land better; or all of
these. He will have
to have all these things firmly in mind so that he
can:
*
build the right kinds of pond.
*
build the right number of ponds.
*
stock the right kinds of fish.
TYPES OF PONDS The
types of pond a farmer can build depend on water
supply, soil, and topography, the factors which were just
discussed. The
two types of pond most often built are barrage ponds and
diversion ponds.
Many aspects of the construction of these ponds are the
same. The main
difference between these two types of pond is the water
source.
Barrage Ponds. These
ponds are usually filled by rainfall or by spring
water. A spring, for
example, sends water flowing through a small valley
or down a slope into a low place.
Or a spring bubbles from the ground
into a natural depression.
The pond is formed by collecting water at the
base of the valley and in the low places.
The farmer does this by building
a wall (dam) which holds the water inside what now is the
pond area.
The wall keeps the water from entering and leaving except as
needed.
<FIGURE>
12p20.gif (486x486)
The number of pond walls the farmer must construct depends
upon the land
and on how he fixes his drainage system.
A barrage pond usually needs
only one wall -- the main wall between the water source and
the pond area.
One kind of drainage system called a sluice (see
"Construction" section)
can be used to let water both in and out of the pond.
There are also a
number of simple drainage systems which can be used that do
not require
any complicated construction.
Barrage ponds should not be built where the flow of water is
too great:
it is difficult to keep the water from breaking down the
wall if the
pressure of the water is too great.
Brooks and streams which flow well,
but not too strongly, make good sources for barrage ponds.
Even when the flow of water is not great, however, barrage
ponds require
overflow channels.
Because, barrage ponds are usually built in low areas,
they are likely to fill up in heavy rains.
Overflow channels are any
kind of system which can be set up to stop the pond from
collecting too
much water. The overflow
takes extra water away from the pond.
If this
extra water is not taken out, the pond wall may break.
Therefore, the
overflow system is needed to help the drainage system handle
the flow of
water when there is too much water in the pond.
The overflow system can be wide grooves cut into the top of
the wall
toward the ends away from the middle; it can be large hollow
tree trunks
which are set into the tops of the wall and work as pipes to
drain the
water into ditches, or even to carry the water into storage
areas for use
later when the water supply is low.
Another kind of overflow can be
ditches, dug into the ground above pond level, which take
the extra water
away when the water rises to that level.
An overflow often is not screened, because if something
large catches
on it, the pressure of the water behind it might cause the
entire wall to
break. This fact
results in a loss of fish at time of flooding.
<FIGURE>
12p21a.gif (486x486)
Diversion Ponds.
These ponds are made by bringing (diverting) water from
another source like a stream or river.
Channels are dug to carry the
water from the water source to the pond.
<FIGURE>
12p21b.gif (486x486)
Diversion ponds can be made in a number of ways.
Sometimes a pond is
dug in flat ground or can be made by slightly enlarging a
natural depression
in the land.
These ponds, like the barrage ponds, require walls depending
upon the
topography of the land, the drainage system used, etc.
A pond dug in
flat ground often requires four walls; a pond built in a
natural depression
may not.
With a diversion pond, the water is always brought to the
pond instead
of running directly into the pond.
Water can be diverted in a number
of ways. For
example, a small stream which gets its water from a larger
stream nearby can be dammed and used as a diversion channel
to feed a
pond. Or water can
be diverted to a pond from an irrigation ditch which
carries water to agricultural crops from a nearby well or
lake.
A farmer may have one diversion pond, or if his space allows
and the
water supply is sufficient, he may have several.
When a series of diversion
ponds is built, they are built in one of two ways:
*
Rosary system.
These ponds are built one after another in a
string.
In this system, all the ponds drain into
each other
and must be managed
as if they were one pond. Therefore, if
the first pond
in the series (the pond with the water inlet)
is full of
predators which must be poisoned, all the other
ponds in the
system have to be harvested (have the fish taken
out) and
drained before the first pond can be poisoned and
drained.
<FIGURE>
12p22.gif (486x486)
*
Parallel system.
In this series, each pond has its own inlet
and
outlet. Therefore, each pond can be
managed as a separate
pond.
Each kind of pond is going to have advantages or
disadvantages depending
upon the farmer's situation.
A parallel system of diversion ponds, in
most cases, is a better system.
But rosary systems are cheaper and
easier to build, and therefore, more possible for some
farmers to undertake.
Also, if the water source is good, and can be kept free of
predators
and unwanted fish, and if the management of the pond is done
well,
a rosary system can be very successful.
Diversion ponds are often better than barrage ponds because
they are less
likely to overflow, and the water source is often more
dependable throughout
the year. But
barrage ponds require less construction and are likely
to be cheaper. In
addition, for some farmers, barrage ponds are the best,
and perhaps the only, way for them to use their land for
fish ponds.
The art of constructing and planning a fish pond or fish
operation is
very much an individual thing.
There are basic ways of using resources,
for example, land and water resources.
But the exact shape and type of
fish pond must be decided by the farmer for his
situation. There are
many ways of making fish ponds which will work, and the
"right" way for
any given farmer is the way which works best for him.
Many aspects of
fish farming are determined by experimenting with pond
operation, but
much can be done by good planning before fish pond
construction.
Therefore, the farmer must look at his sites and consider
the types of
ponds he can build from the viewpoint of the number, size,
and depth of
the ponds he is going to need.
If, for example, the farmer thinks he
has a good area for a diversion pond, but hits solid rock at
1m and needs
a pond 2m deep, he can find this out before he invests a
great deal of
time and money. If
he has room for two small diversion ponds and a
barrage pond, or for a large diversion pond and a barrage
pond, he can
base his decision on what kind of pond to build upon the
number, size,
and depth of pond he needs for what he will be doing.
The Number of Ponds.
The number of ponds depends on the possible sites
and on what the farmer plans to do with his fish ponds.
If he is going
to raise fingerlings to market size, he will need one or a
few "rearing"
ponds. If a farmer
plans a larger operation in which he will breed fish
for the eggs and fry, he will need space for nursery pond,
rearing pond,
and a pond for brood stock.
Nursery ponds can hold eggs and fry until
they are fingerling size; rearing ponds hold the fingerlings
until they
are market size; brood ponds hold the fish to be used for
breeding.
It is possible to breed fish in a corner of a large, single
pond, and a
farmer interested in raising fish for his own use may want
to do this.
But a farmer interested in marketing fish probably will want
at least
two large ponds. If
he has two medium-large ponds, he can use one for
rearing fingerlings and one for broodstock.
Eggs and fry can be taken
care of in very small ponds or even containers.
The Size of Ponds.
The size of ponds depends upon the same factors --
topography, water supply, and need.
Nursery ponds usually are smaller
than rearing ponds because the fry are very small.
The size of nursery
ponds depends on the fish species being cultured.
In fact, eggs and fry
can even be kept in washtubs, oil drums or any other such
container which
holds enough water for the number of fry and is supplied
with enough
oxygen.
<FIGURE>
12p24.gif (486x486)
As the fish grow, they need more space.
So rearing ponds are usually
bigger than nursery ponds, and brood ponds are bigger than
rearing ponds.
Sometimes a farmer will have to choose between one large
pond or several
smaller ponds. His
site would allow him to decide either way.
Here are some advantages of small and large ponds:
Small Ponds: *
harvest easily and quickly
*
drain and refill quickly
*
treat for disease easily
*
are not eroded by wind easily
Large Ponds: *
cost less to build per hectare of water
*
take up less space per hectare of water
*
have more oxygen in the water
*
can be rotated with rice or other crops
For most farmers, a few small ponds are better than one or
two large
ponds. Farmers must
also manage their agricultural crops, and it is
difficult for them to manage large ponds.
Also, most farmers just do
not have a lot of land.
A good size for a single fish pond is probably
between 1 and 5 ares (100 and [500m.sup.2]).
Farmers are going to be most interested in working the fish
pond into an
already going farm as simply and easily as possible.
This is why
culturing fish in rice paddies is popular in some
areas. In fact, fish
ponds can be set up in almost any area where a rice paddy
can be located
-- even on steep hillsides.
Small ponds are easier to care for and construct.
As a farmer gains
experience, he can go on and build larger ponds.
Starting small is a
good idea until the farmer feels he knows what he is doing
and is successful.
Depth of Ponds. The
depth of ponds depends upon the fish being grown.
Fish species like different kinds of food, and the depth of
the ponds
affects the kinds of food produced by the pond.
A common carp, for
instance, eats worms and other bottom organisms and must
have a pond
that is not deeper than 2m.
But when the carp are fry, they eat only
plankton, the tiny free-floating plants and animals
suspended throughout
the water. So
nursery ponds for carp fry are often only 0.5m deep.
(As mentioned before, eggs and fry can be taken care of in
almost any
container which holds enough water and has enough oxygen.)
Other fish feed at other levels in the ponds depending on
their life
stage and on their own food preferences.
A very deep pond will not
produce as much food because the sunlight cannot light the
water below
a certain depth, and the plankton will not be able to make
oxygen for the
fish (see water quality).
On the other hand, a very shallow pond might
be turbid, covered by water plants easily, and become very
hot. Most
pond owners make sure that the water depth at the edges of
the pond is
at least 75cm to discourage water plants.
It is best if the pond is
about 75cm deep at the shallow end and up to 2m deep at the
deepest end.
This will give the best results with most pond fish.
THE ONE-POND OPERATION
If the farmer's site can only have one
pond, his decision is easy.
It is hard to breed fish when only one pond
is available.
Usually a single pond is used only for rearing fish from
fry or fingerlings to market size.
This is the case in small, backyard
fish ponds that are used to supply fish for only one
family. A good
minimum size for such a pond is [15m.sup.2] in area and 1m
deep. A smaller
pond would probably not be worth the effort to build and
maintain.
A single pond is stocked with the fry or fingerlings.
For example, a
pond of the size mentioned above could be stocked with 60
fingerlings.
These young fish are cared for until they reach adult
size. Then the
pond is harvested (the fish are taken out).
The pond area can then be
prepared for a new batch of fish and stocked again.
One pond can provide a good food source for the family.
However, rearing
fish means that somewhere there must be a source of fry or
fingerlings
for use in the pond.
The farmer must check his area carefully, so that
he is sure the young fish are available before he builds one
pond.
The source can be a river where he collects the young fish,
or a local
fish farm which breeds fish to supply farmers who have small
ponds, or a
government hatchery where the farmer can buy the young
fish. If the
farmer decides that he wants to breed fish in his pond, it
is possible
to breed some fish inside small nets placed in the
pond. A single pond,
though, is usually used just for rearing fry or fingerlings
to a good
size for food and market.
While one pond usually means that the farmer is wise to
concentrate on
raising one batch of fish from fry or fingerlings to market
size, he
still must decide what kind or kinds of fish he will raise
in his pond.
He can raise one kind of fish alone (monoculture), or he can
raise
several kinds together (polyculture).
<FIGURE>
12p26.gif (393x393)
MONOCULTURE
Monoculture is the culture of only one species (kind) of
fish in a pond. It
can be tilapia of one species, common carp, or any
other single fish species.
Monoculture has some advantages.
One advantage is in intensive fish
culture practices, where fish are fed a lot of supplementary
foods for
fast growth. It is
easier to give there foods if there is only one type
of fish in the pond.
Another possible advantage is that monoculture
gives greater control over the age and sex of the fish.
In monocultures,
fish can be of all different ages and life stages, or they
can be
separated into fry, fingerlings or brood stock.
<FIGURE>
12p27a.gif (437x437)
A monoculture allows a farmer who is unfamiliar with fish
farming to get
to know his one type of fish very well.
And there is some advantage to
this.
<FIGURE>
12p27b.gif (393x393)
One disadvantage of a monoculture
pond is that it is more likely
for a single disease or parasite
to kill all fish in the pond.
Different fish are susceptible
to different diseases.
If only
one fish type is present in the
pond, a bad fish disease could
easily infect and kill all the
fish if it were not stopped in
time.
<FIGURE>
12p27c.gif (437x437)
In monoculture ponds, fish are harvested
selectively by using nets which
have meshes of different sizes.
For
example, if the farmer wishes to
harvest larger fish for market or
breeding, the net will not catch or
hurt the fry or fingerlings, because
they are too small to be caught by
a large-mesh gill net.
This allows
the farmer to keep his pond in
operation and producing fish for
food all year.
Monoculture is the most common kind of pond culture.
For a small fish
farmer who is most interested in having a nearby, year-round
supply of
protein (and who does not have a lot of time or interest to
give to the
pond), a monoculture may be a very good idea.
POLYCULTURE
<FIGURE>
12p28a.gif (393x393)
Polyculture is the culture of two or more fish species
together in a
pond. A good
polyculture uses the natural food sources in a pond better:
if the polyculture is mixed correctly, each of the species
eats a
different food from the pond.
<FIGURE>
12p28b.gif (317x317)
Polycultures are more
resistant to disease.
Disease, if present,
usually attacks the
smaller, weaker fish,
and the healthier fish
continue to live and
grow.
Fish stocked in a polyculture must be able to live
together. And living
together successfully means that the fish put into the pond
together do
not all need to eat the same food.
A polyculture can have fish of any
size or age -- as long as a balanced relationship is
maintained.
Some examples of polycultures are:
*
fingerlings of two or more species stocked
together in a
fertilized pond
and left to grow. A good mixture in
this
kind of
polyculture is a mixture of Chinese carp -- silver,
grass, and
bighead carp stocked together. The
silver carp
eats
phytoplankton; the grass carp eats pond vegetation;
the bighead
carp eats zooplankton.
<FIGURE>
12p29a.gif (534x534)
*
A few large fish (brood size) are stocked
with fingerlings
of another
species in a pond and left alone. A
good example
of this is
stocking tilapia fingerlings together with a few
adult-sized
Clarias catfish. The catfish feed on
bottom
organisms and
serve as a population control on the fry that
are produced in
the tilapia ponds. Since one of the
problems
which can be
associated with culturing tilapia is overpopulation,
this is a very
complementary relationship.
<FIGURE>
12p29b.gif (393x393)
*
Another example of this type of polyculture
is a stocking
of any kind of
fingerlings mixed with a few large grass
carp for weed
control.
<FIGURE>
12p30.gif (348x480)
Polyculture is a good way to use a pond, especially if there
is only one
pond to use. A
careful examination of local fish and their habits should
tell a farmer what kinds of polycultures are possible in his
pond. The
important thing to remember is that the fish must not
compete with each
other. If stocked
and managed correctly, polyculture ponds can give
maximum production to a fish farmer.
In very practical terms, the farmer
could raise as much as three times more fish in a
polyculture of three
species than he can raise in a monoculture pond of the same
size.
MONOSEX CULTURE A
word should be said about monosex culture, even
though few farmers will choose or be able to choose this way
of operation.
Monosex culture means growing only one sex of one species of
fish in a
pond. When only
males or only females are stocked in a pond, all the
energy of a fish goes into growth and not into reproduction.
An all-male stocking has faster growth rates than a mixed
stock of males
and females. So some
farmers try to stock only males or females in a
pond. One fish
species that often is used in monosex culture is tilapia.
Tilapia reproduce at a very small size, but when separated
by sex, they
do not develop their reproductive organs, yet continue to
grow.
One way to stock a monosex pond is to separate the fish one
by one
according to sex during the breeding season.
Often, at this time, fish
change color, and it is easier to sort fish by sex.
Then the fish can
be grown to a larger size.
In another method, people have been trying to obtain fish of
all one sex
by putting two different species of tilapia into a
pond. When these fish
breed, they produce either a monosex culture or a sterile
hybrid. Three
crosses do now produce 100% male offspring.
Crosses of Tilapia which Produce 100% Male Offspring:
MALE
CROSSED WITH FEMALE
Tilapia macrochir
X
Tilapia nilotica
Tilapia mossambica
X
Tilapia nilotica
Tilapia hororum
X
Tilapia mossambica
There are no crosses that produce 100% female offspring as
yet. Males
are preferred because they continue to grow during the
breeding season,
when there are no females present -- even though they (the
males) continue
to build their nests in preparation for mating.
Monosex culture is a valuable method of pond culture, but is
usually
difficult to do: the
hybrid crosses are very new; hand-sorting fish by
sex causes many of the fish to die from stress.
Even if the fish are
sorted without stressing them, one fish of the opposite sex
that
accidentally finds its way into the pond can ruin the whole
monosex
culture. So monosex
culture is generally not practiced by small-scale
fish farmers.
THE MORE-THAN-ONE-POND OPERATION
A farmer who has a larger
area to work with might wish to consider having two or three
small ponds.
Perhaps two ponds would be diversion ponds, and the third a
barrage
pond fed by a spring.
Perhaps the farmer has room for only two barrage
ponds. He does not
want to keep eggs and fry in the ponds because it is
harder to protect eggs and fry in barrage ponds.
This does not mean he
cannot breed fish.
He can keep eggs and fry in an oil drum, washtub,
or anything else as long as the water is clean and contains
plenty of
oxygen.
With three ponds, one pond can be the rearing pond in which
fingerlings
are raised to market size; one can be used to keep brood
stock; and the
third, and perhaps the smallest, can be used as a nursery
pond where the
eggs hatch and the fry grow to fingerling size.
If the farmer does not
plan to breed fish, then he can use all three ponds as
rearing ponds.
He should not do this, however, without thinking ahead to
the harvest
and making plans for marketing the fish he will grow, or
preserving the
fish for sale or use later.
<FIGURE>
12p31.gif (437x437)
The major difference between a large farm operation and a
small one may
be only the number of ponds.
Three ponds is enough to have a full-fledged
operating fish farm which includes breeding, selling fry and
fingerlings
to other farmers, and raising fry and fingerlings to market
and brood
size. Once the
farmer is a skilled pond manager, these ponds should do
well and provide a good return on his investment.
Until the farmer is experienced, however, it is better for
him to start
with small efforts and a smaller operation.
Small pond failure is not as
severe. Once the ponds
are working well, the farmer can expand and build
more and/or larger ponds.
But he should be encouraged to start small.
There are a lot of factors in fish pond management that are
learned best
by experience. But a
bad experience will discourage, rather than encourage,
the pond owner.
A FINAL WORD ON PLANNING PONDS
Good planning is a must for a
successful fish pond operation.
It is during the planning process,
before any money or a lot of time and energy is spent, that
many problems
can be solved.
The farmer should keep in mind while planning that ponds do
not have to
have expensive equipment in order to work well.
Far more important than
the equipment are 1)
an understanding of the general principles involved,
2) the selection of
a fish or fishes that will do well in his pond (see
next section, "Selection of Fish"), and 3) good
daily management of the
pond (see section 6, "Managing the Pond").
3
Planning: Selection of Fish
The farmer now has a firm idea of his site and the types of
ponds it is
possible for him to build.
He also should know what he wants to do with
his ponds -- raise fish for food or run a fish-marketing
business. Now
he must consider very carefully what type or types of fish
he is going
to raise in his ponds.
The success of the pond depends upon choosing
the fish that will grow best in the type of ponds and
conditions that a
farmer is planning.
The following pages give some:
1) general information on
characteristics
of fish, and 2)
detail about certain fish which have proved to be good
pond fish and why.
This information should serve as a guide to a farmer
trying to decide which fish will do best in his ponds.
Characteristics of Fish
The major body parts of all fish perform the same functions,
and they
are located in about the same places on any different fish's
body. But
the size, shape, and color are often different, and these
differences
help tell the fish apart.
Knowing how a healthy fish looks is important.
All fish have a tail consisting of the caudal peduncle and
the caudal
fin. The fish's fins
help it steer through the water and hold it
upright in the water.
Often a sick fish cannot steer or flops over on
its side. Other fins
on the body include:
*
Pectoral -- usually located on the sides of
the fish behind
the head.
*
Pelvic -- usually located towards the rear
of the body where
the hips would
be if the fish were a four-legged animal.
*
Dorsal -- runs along the top of the
fish. May be single or
double.
The second dorsal fin is sometimes called
the soft dorsal
fin.
<FIGURE>
12p34.gif (480x534)
*
Anal -- usually located right behind the
aral vent (anus) on
the rear bottom
end of the fish.
Most fish have eyes, but even with eyes fish cannot see very
well.
All fish have gills.
The gills are covered by a flap called the
Operculum. The gills
are extremely important. Fish take in
water
through their mouths.
The water is then passed through the gills
which remove the oxygen and nutrients from the water.
The water
is then passed outside of the body of the fish through the
gill slits.
It is possible to tell a lot about a fish's health and
eating habits by
looking at its gills.
Fish with many, many feathery gill rakers and
few if any teeth eat the smaller foods in the pond.
Fish with few and
larger gill filaments eat the larger particles from the
pond. Healthy
gills are a bright red color.
If the farmer sees fish with gills that
do not have this healthy red color, or have white spots all
over, for
example, he will know that fish is not healthy and should
not be bought
or placed in his pond.
Or if the fish is already in his pond, he knows
he must take steps to get rid of the disease before it
troubles more fish.
Other identifying parts that all fish have are the mouth,
the genital
openings (to reproductive organs), and the lateral
line. The lateral line
is a small line of nerve cells which runs along the length
of the body
about midway on the side of the body.
Sometimes the lateral line is
covered by a layer of scales; sometimes it is a different
color than the
rest of the body. In
any case, the lateral line is an area of sensitivity
that helps the fish feel pressure and temperature changes in
the water
around it.
Some fish, like catfish, also have barbels, small
projections that hang
down from the sides of the mouth.
Barbels help the catfish sense its
surroundings, find food, and attract small fish to the
catfish so that
it can eat them.
<FIGURE>
12p35a.gif (393x437)
When a farmer breeds fish he will want to be able to tell
the difference
between male and female fish.
This can be difficult with some fish.
However, some fish change color in the breeding season
(tilapia, for
example), so they are easy to identify by sex.
Some fish can be classified
according to the color and size of their genitals.
The separation
of fish by sex is best learned by actual experience in the
pond.
<FIGURE>
12p35b.gif (486x486)
When the farmer goes to buy fish, he must already know what
healthy fish
look like. It is
very important that he be as familiar as possible with
each of the fish he decides to raise.
He must know the characteristics
of that fish and its life cycle, its eating and breeding
habits, etc.
The farmer who begins any fish pond enterprise without
having this kind
of information is inviting failure.
And if it is a new venture, it is
particularly important that the farmer's first effort be as
successful
as possible.
The Life Cycle of Fish
Fish start life as fertilized eggs.
The eggs grow and then hatch into
small fish, called fry.
The fry are attached to the yolk sac which is
the leftover part of the egg they hatched from.
The yolk sac provides
food for the fry during the first few days after hatching.
<FIGURE>
12p36.gif (486x486)
After the yolk sac is gone, the fry searches for food in the
water. All
fry eat the tiny suspended and swimming plants and animals
called plankton
in the water.
Plankton are hard to see, but if a farmer puts some
of his pond water into a glass container and holds it up to
the light so
that the light shines through the water, he can see the tiny
plankton
floating in the water.
The length of the fry stage depends upon the
species of fish.
Usually a fish is a fry at least until the yolk sac is
absorbed. Fry range
from 2mm to 30mm in length. This growth
process can
take 2 to 6 or 8 days depending upon the type of fish.
As the fry grow bigger, they are called fingerlings.
They are called
fingerlings because at this stage of the growth cycle, they
are about the
size of a person's finger.
Fingerlings vary in size -- from 4-1Ocm.
Above 10cm, the fish is better called a
post-fingerling. The adult fish
ranges in size; some can be as large as 2m long and weigh
22kg. An adult
fish is a fish which is sexually mature.
Fingerlings have different eating habits from fry; they are
now much
bigger and can eat larger pieces of food.
As fingerlings, the fish begin
to show that they like certain foods better than other
foods. Each kind
of fish chooses its own kind of food, depending upon his
needs and what
is available. For
example, a carp fry will eat plankton; as a fingerling,
the carp eats pieces of decayed matter and insect larvae; as
an adult
the carp will eat plankton, decayed matter, insect larvae,
worms, snails,
and almost anything that is on the bottom of the pond.
Common carp, for
example, are called "bottom feeders," because they
eat food from the bottom
of the pond.
<FIGURE>
12p37.gif (486x486)
The food preference does not always
change as the fish grows.
Some fish,
like the silver carp, eat plankton
their whole lives.
When the fish
reach adult size, they will sexually
mature in the right conditions.
Brood fish are sexually mature fish
which are chosen as good fish to
breed (spawn), produce eggs and
begin the whole cycle again.
This
is called the life cycle of a fish.
Knowing how the fish in the pond
grow, and the foods they require at
each stage in the life cycle, is very
important for good pond management.
Choosing Pond Fish
Choosing fish to grow in ponds can be difficult.
A good pond fish has
certain characteristics which help it grow successfully in
ponds. There
are some fish which will not adapt to pond conditions and
cannot be used
in pond culture. A
pond is very different from a natural waterway:
*
There is usually no water flowing through a
pond. Some fish
need to live
where there is quite a bit of current in the
water, rather
than in a quiet pool of water.
*
The food that is already in the pond is all
that is available
to the fish,
unless extra food is put in by the farmer.
*
There is only a certain amount of water and
pond area in which
to move about.
There are many fish that do grow well in ponds.
Some of these are fish
grown locally; some are fish grown in other parts of the
world.
Many governments today are introducing exotic fish species
(these are
kinds of fish not native to that country) into fish pond
programs.
They do this for three reasons:
*
Some
Introduced fish grow better and faster than native fish.
*
Some introduced fish are preferred by people
for eating (over
local fish).
*
The offspring of a cross between a local
fish and an introduced
fish sometimes
grow faster and taste better than either of the
parent fish
(this is called hybrid vigor).
But exotic fish must be watched and used very
carefully. They must not
escape into local waters.
Some exotic fish which escape create problems
in natural waters when they begin to compete with local
fishes for food.
Also, introduced fish can carry diseases or parasites that
are fatal to
native fishes.
There are certainly a number of fish in the natural
waterways of your
area which will grow well in ponds.
Native (local) fish are usually
easier to use because they are adjusted to local water and
climate
conditions.
If at all possible, farmers should be encouraged to start
their ponds
using a tested pond fish which is locally available and is
well-liked
by people in the area.
It can be a fish from the list given here or
one chosen from a list prepared in your area.
The important points
are that the farmer be able to sell any fish he wishes to
sell, that
the fish can grow in ponds, and that there is brood stock
available
locally.
Fish Used in Pond Culture
Here are some characteristics that good fish for pond
culture will have.
Certainly it may not be possible for a farmer to determine
whether a
certain fish has all these characteristics right away,
particularly for
those local fish not discussed in detail here or those newly
introduced
to pond culture. But
good pond fish all have certain characteristics:
the more certain a farmer can be that the fish he chooses to
raise fit
these descriptions, the more sure he can be of his
success. Good pond
fish are:
*
available locally
*
able to reproduce (breed) naturally in your area.
*
able to live in a confined space (the pond).
*
able to find the right foods in ponds.
*
fast-growing.
*
relatively free of parasites and diseases.
*
known and liked as a food fish in the area.
Some fish that fit these criteria for good pond fish and are
now grown
in ponds all over the world are named here.
Though they all are grown
in ponds, each has certain characteristics which mean that
it will grow
better in some kinds of ponds better than other ponds.
Of course, these
fish are not the only fish that can be used in ponds.
But they are named
here because they have been tested in ponds, and they can
grow well under
pond conditions. All
of these fish are warm water fish.
SCIENTIFIC AND COMMON NAMES OF FISH USED IN POND CULTURE
Please
note: Each fish has a scientific name
which is
always the
same. The common name, however, can be
different
from one country
to the next. It is a good idea for
anyone
who works with
fish to know the scientific name.
Genus -
species
Common name
1.
Anguilla japonica
eel
2.
Aristichthys nobilis
bighead carp
3.
Barbus gonionotus
tawes
4.
Carassius auratus
goldfish
5.
Carassius carassius
crucian carp
6.
Catla catla
catla
7.
Chanos chanos
milkfish
8.
Cirrhina molitorella
mud carp
9.
Cirrhina mrigala
mrigal
10. Clarias
batrachus
catfish
11. Clarias
macrocephalus
catfish
12. Ctenopharyngodon
idellus grass
carp
13. Cyprinus
carpio
common carp
14. Helostoma
temmincki
kissing gourami
15. Heterotis
niloticus
-
16.
Hypophthalmichthys molitrix
silver carp
17. Labeo
rohita
rohu
18. Mugil
cephalus
mullet
19. Mylopharyngodon
piceus black
carp
20. Osphronemus
goramy
gourami
21. Serranochromis
robustus -
22. Tilapia
macrochir
tilapia
23. Tilapia
melanopleura
tilapia
24. Tilapia
mossambica
tilapia
25. Tilapia
nilotica
tilapia
26. Trichogaster
pectoralis
snakeskin gourami
27. Trichogaster
trichopterus
three-spot gourami
Following is specific information on some of the more
popular pond fish.
COMMON CARP
The common carp, Cyprinus carpio, is a favorite warm water
pond fish.
Common carp are used as a pond fish because they:
*
spawn easily in ponds.
*
do not get sick easily.
*
tolerate wide ranges of temperature and pH
(factors of water
quality
discussed in detail later).
*
eat all kinds of food, from zooplankton to
decaying plants.
*
have a very good growth rate.
*
accept supplementary foods.
<FIGURE>
12p41.gif (393x393)
Common carp generally are a grey-green color.
However, they also can be
gold, yellow, orange, pink, blue, green, or grey.
They spawn all year
round in warm waters, and they can be made to spawn by the
pond owner if
they do not spawn naturally.
Common carp are good to eat when they are
cooked properly.
They can be grown in ponds by themselves (monoculture)
or in ponds with Chinese or Indian carp (polyculture).
Some of the yields gotten in various countries by stocking
common carp in
monocultures are shown in the following table.
Yields,
Country
Culture methods
kg/hectare
Czechoslovakia
Growth in ponds with ducks
500
Guatemala
Intensive culture in ponds
4,000
India
Natural growth in ponds
400
Growth in ponds with management
1,500
Indonesia
Intensive culture in ponds
1,500
Japan
Intensive culture in ponds
5,000
Nigeria
Commercial culture with
fertilization and feeding
371-1,834
Philippines
Intensive culture in stagnant water
5,500
United States
Intensive pond culture with
inorganic fertilization
314
Source:
Bardach, et al (1972)
Conclusion: Common
carp are a very easy fish to breed, keep, and harvest,
so a fish pond that relies on common carp will probably do
well. Common
carp are a good fish for a farmer to use for his first
effort. With good
management, common carp will continue to produce healthy
eggs and fry
until they are too old (above 5 years of age).
TILAPIA
The Tilapia genus (family Cichlidae) contains at least 14
species, which
are all good pond fish.
The color of the fish differs only slightly
depending upon species; tilapia are generally dark brown to
black in
color. The most
common species grown in ponds is the Tilapia mossambica,
also called the Java tilapia.
It has been introduced throughout the world
and is easy to find in most places.
Tilapia:
*
are hardy fish, resistant to disease.
*
breed easily in ponds.
*
grow rapidly.
*
taste good.
*
can withstand wide temperature ranges.
<FIGURE>
12p42.gif (437x437)
Tilapia are herbivorous:
some species eat higher plants; some eat
phytoplankton. Both
the Java tilapia and the Nile tilapia (Tilapia
nilotica) do well in very enriched waters (waters polluted
by sewage).
All tilapia have slightly different eating habits, depending
on the
species.
Tilapia reproduce every month or so, once they become
sexually mature.
They then take very good care of their own eggs and fry in
ponds. If
the farmer plans to breed and raise fry, this fish is a good
choice
because the fish themselves take care of the fry at a stage
where many
fish of other species die easily.
The major problem with raising tilapia
in fish ponds is that they become sexually mature at a small
size, and
begin to reproduce instead of to grow further.
It may be necessary to
separate the tilapia by sex before they are old enough to
reproduce. Or
it may be necessary to introduce catfish into the pond to
control the
population of small fish.
Conclusion: Tilapia
species have many possibilities for pond culture.
Their fast growth rate, ease of breeding, good taste and
hardy bodies
make them a good choice, particularly for the first-time
fish farmer.
CHINESE CARPS
Other kinds of carp, besides the common carp, often are
grown in ponds.
Most commonly used are the Chinese carps.
Some of these are:
<FIGURE>
12p43a.gif (437x437)
*
Silver carp (Hypophthalmichthys
molitrix). This fish eats
phytoplankton,
but will accept rice bran and bread crumbs.
The silver carp
gets its name from its silver color. It
has
very small
scales.
<FIGURE>
12p43b.gif (437x437)
*
Bighead carp (Aristichthys nobilis).
This fish feeds mainly
on
zooplankton. It is a dusky green color
on top which fades
to a pale green
color on the abdomen. It also has small
scales.
<FIGURE>
12p44.gif (437x437)
*
Grass carp (Ctenopharyngodon idellus).
This fish is an
herbivore and
eats water vegetation (but also will eat
almost
anything). The grass carp is also
silver-colored,
but has a
darker grey area running along the top of the body.
It grows larger in size and has larger
scales than a silver
carp.
Other chinese carps like the black carp (Mylopharyngodon
piceus) and the
mud carp (Cirrhina molitorella) are bottom feeders.
This difference in
eating habits is very important in fish pond culture.
It is the reason
why polyculture, or growing a number of fish species in one
pond can be
successful. When one
kind of fish is stocked alone in a monoculture,
the foods in the water not eaten by that type of fish are
wasted. In a
polyculture of the above three species of Chinese carp, for
example,
three kinds of food are being eaten.
The following table gives some examples of polyculture mixes
and of how
many fish of each kind can be stocked in a pond.
For example, Pond I is
stocked with silver, bighead, grass and common carp.
STOCKING RATES OF CHINESE CARPS IN PONDS
3 TO 7
METERS DEEP IN KIANGSU PROVINCE, CHINA
Weight of Number of
Yearlings per hectare
Species Yearlings,
grams
I
II
III IV
Silver and
bighead carp
500
4,500
4,500 9,000
9,000
Grass carp
500 600
-
3,000
Black carp
500 -
450
3,000
Common carp
200 200
200
200 200
TOTAL:
5,300
5,150
12,200 12,200
Source:
Bardach, et al (1972)
The preceding table shows polyculture mixes:
as you can see, common carp
can also he used in polyculture with Chinese carp.
Chinese carp are
grown in ponds because they grow well in polycultures, and
they are very
good to eat. The
silver carp grows faster and is tastier (according to
some farmers) than common carp.
The grass carp is most often used to
control weeds in the pond.
In fact the grass carp does a better job of
weed control than do chemicals.
The grass carp is perhaps the most interesting
of the Chinese carp and is now being studied by scientists
in
many countries to find better ways of breeding it in ponds.
A farmer might run into problems raising Chinese carp -- if
he does not
look into his local situation very well.
Farmers will have to have a
source of Chinese carp fry from a government hatchery or a
local breeder
before trying to raise Chinese carp.
The carp only breed once a year,
and then, in most cases, only with help from man.
Also, Chinese carp are
very susceptible to diseases.
Then, because they are delicate fish, they
must be handled very carefully, or they will be injured.
Conclusion: A farmer
just beginning a fish pond probably would not want
to breed Chinese carp, but he certainly should be familiar
with these
fish and how they might help his ponds.
For example, even two or three
large grass carps placed in a pond with many fish of one
other species,
could be valuable for keeping a pond balanced.
INDIAN CARP
There is one last group of carp often cultured in
ponds. These are the
Indian carp. Indian
carp are further divided into minor and major carp.
The major carp of India are the catla (Catla catla), the
rohu (Labeo rohita),
and the mrigal (Cirrhina mrigala).
The minor carp are the reba, the bata,
the sandkohl, and the nagendram fish.
The Indian major carp will not
spawn in standing water, so special ponds are built in India
to provide
a flow of water for these fish, who must have running water
in which to
spawn. The Indian
carp can be made to spawn by man, but this is a difficult
process (see "Managing Brood Stock").
However, there seems to be
no reason why the Indian carp cannot be spawned in ponds in
places where
ponds can be constructed to provide constantly running water.
<FIGURE>
12p45.gif (437x437)
Conclusion: A farmer
who has only a small pond should not try to breed
Indian carp. Indian
carp can be grown in polycultures with common carp,
but are not as good or fast growing in ponds as the Chinese
carp.
Indian carp are also susceptible to many diseases.
This is a fish for
an experienced fish farmer who is interested in, and able
to, experiment.
GOURAMI
The gourami (Osphronemus goramy) is a very good pond
fish. It is
originally from Indonesia, but now is grown all over Southeast
Asia.
Gourami possess an accessory air-breathing organ, which
means that they
can survive in waters that are low in dissolved oxygen.
This makes it'
an important fish in areas where the temperature remains
high and there
is little water for certain periods of the year.
Gourami spawn all year
round in warm water conditions.
Gourami:
*
spawn easily all year round in warm waters.
*
taste good.
*
are easy to breed.
*
accept a variety of foods.
*
are hardy.
<FIGURE>
12p46.gif (437x437)
Conclusion: Gourami
are good fish for a first-time fish farmer.
And
they are certainly a fish to be considered very thoughtfully
by farmers
who live in areas that remain very hot and dry for periods
of the year.
The gourami is used to these conditions, and there are other
pond fish
which would not do well at all under these conditions.
CLARIAS CATFISH
Clarias catfish are found throughout Asia, India, and
Africa, as well as
the Middle East. The
species most often used as pond fish are Clarias
macrocephalus and Clarias batrachus.
Clarias macrocephalus is preferred
for its good taste; Clarias batrachus grows faster.
<FIGURE>
12p47.gif (437x437)
These catfish have accessory air-breathing organs; they can
even crawl
out of ponds to look for food.
Because they can live in shallow ponds,
these catfish are sometimes used in culture with rice (see
paddy culture).
They are scavengers, which means they will eat just about
anything.
However, they prefer to eat worms, snails, and other
fish. They are
often used in polycultures with tilapia where they serve as
predators on
the very small tilapia.
They will eat supplementary foods, and give very
high production in ponds.
In Thailand, Clarias catfish yield about
97,000kg/ha when they are fed supplementary foods.
These catfish are
hardy: they
sometimes get external parasites, but these do not kill the
fish.
Conclusion: The
catfish are another good fish to be raised in areas
where high heat and long dry spells are found.
They are good to eat,
easy to keep, and can be used in ponds in a number of
ways. Certainly
a farmer who already cultures paddy rice might be interested
in considering
adapting his paddy to catfish culture.
TAWES
The common name tawes is applied to three species of fish --
Barbus
gonionotus, Puntius javanicus, and Puntuis gonionotus.
These fish
usually are used in fish ponds for vegetation control, in
polycultures
with Chinese carp.
Tawes are able to spawn all year round, but they
most often spawn in the rainy season.
Tawes need well-oxygenated water
with a strong current to spawn.
Tawes feed on soft water plants, but will
also take rice bran.
There is not a great deal known about the tawes at
present, but it can be used in polycultures when the grass
carp is not
available.
<FIGURE>
12p48a.gif (437x437)
Conclusion: A farmer
starting a polyculture certainly might be interested,
in using this fish.
However, first-time fish farmers with limited space
would not want to try breeding this fish.
HETEROTIS NILOTICUS
The Heterotis niloticus spawn easily in ponds.
The mature fish will
build a grass-walled nest in the weeds at a pond's edge and
spawn inside
this nest. They
spawn when water is low and very warm, at the end of
the dry season. The
mature fish feed only on plankton, but in a pond
they will accept supplementary food.
This fish has a swim bladder which
can serve as an accessory air breathing organ.
<FIGURE>
12p48b.gif (437x437)
Conclusion: There is
not yet a great deal known about the Heterotis
niloticus as a pond fish.
But it seems that it is a good choice of fish
for warm climates and warm waters.
A farmer who lives in such a climate
might find raising, and even breeding, this fish quite easy
-- particularly
in a very well-fertilized pond.
OTHER GOURAMIS
These are the snakeskin gourami (or Sepat Siam -- Trichogaster
pectoralis),
the three-spot gourami (Trichogaster trichopterus), and the
kissing
gourami (Helostoma temmincki).
All of these fish taste good.
And they
breed easily in well-oxygenated, warm water.
They do require a pond which
has a good growth of vegetation (particularly Hydrilla
verticillata).
<FIGURE>
12p49.gif (437x437)
Conclusion: In a
pond situation such as that outlined above, these
gouramis are easy to breed and raise.
They are a good fish to use in
polycultures with other gouramis, tilapia, and common carp.
MILKFISH CULTURE
The milkfish (Chanos chanos) can be raised in freshwater
even though it
is primarily a brackishwater fish, and will not breed in
ponds. The fry
are caught along the shoreline at breeding season (the rainy
season) and
transferred to freshwater ponds.
Milkfish culture is done for the most
part in the Philippines and in some other Southeast Asian
countries, like
Indonesia and Taiwan.
Adjusting (acclimatizing) the fry from the saltwater to the
freshwater
pond is hard to do; many fish die if the adjusting process
is not done
well. Therefore,
milkfish usually are cultured in brackishwater ponds
only; the use of milkfish in freshwater ponds is not
widespread. Milkfish
feed on a complex of bottom algae, and, recently, it is
reported
they also feed on phytoplankton.
Milkfish are prized for their beauty
and their good taste, though they have many, many small
bones.
<FIGURE>
12p50a.gif (437x437)
Conclusion: This is
not a fish for the first-time fish farmer.
In fact,
it is not a good choice for any farmer unless he has a
saltwater pond; is
interested in trying to acclimatize the fish to a freshwater
pond; or can
buy milkfish from a source that has them already in a
freshwater pond.
EEL CULTURE
Eels (Anguilla sp.) have been cultured in Japan and Taiwan for
years.
Eels are very much a luxury food and are not normally grown
alone in ponds
outside of these two countries.
The eels are grown in ponds in polyculture
with other fishes and are particularly useful in polyculture
with species of tilapia because they eat the smaller
tilapias. The eels
used in Taiwan (Anguilla japonica) spawn in the sea and the
fry (called
elvers) swim upstream and are collected by dealers.
Eels must be fed
supplementary feeds like pellets made of trash fish.
Conclusion: It is not
recommended that farmers work with eels because
they must be fed protein and are not very efficient
converters of food.
Also, eels cannot be bred in fish ponds.
<FIGURE>
12p50b.gif (437x437)
OTHER POND FISH
Some other fish grown in ponds are the goldfish (Carassius
auratus), the
crucian carp (Carassius carassius), and Serranochromis
robustus. Any
of
these fish can be grown in polycultures with Chinese, common
carp, and
tilapia.
Conclusion: The use
of one of these fish in a pond stocked with other,
more important fishes, results in an increase in yields of
both species.
In polycultures these species can utilize other food sources
and also
act as predators and weed controllers.
<FIGURE>
12p51.gif (540x540)
One other fish species used in freshwater ponds is the
striped mullet
(Mugil cephalus).
Like the milkfish, the mullet is primarily a saltwater
fish, and its fry are collected as they swim upstream.
Recently the
mullet has been made to spawn by man, but this is difficult
to do because
mullet are very sensitive to handling.
However, mullet can survive in
wide temperature ranges and are herbivores, so some farmers
may want to
try mullet.
A CLOSING NOTE ON FISH
All these fish have been and are now being cultured in fish
ponds around
the world. However,
as stated before, they are not the only fish which
can be grown in ponds.
In every area there are a number of fish in
natural waters that could be grown in fish ponds.
So you might find it
a good idea to experiment with local fish in your ponds, to
find those
fishes that might be available to farmers in your area for
use in their
ponds. It is better
for an extension worker to do the experimenting
than it is to have a farmer risk wasting his time or money,
or even more
importantly, risk failure.
If a farmer fails, he may not want to try
again.
4 Fish Pond
Construction
Construction of a large pond can be very expensive if labor
is hired,
machines are used, and expensive equipment is rented.
For example, in
the Philippines, a one-hectare pond having two concrete gates
and walls
3m high x 3m wide recently cost US$1,522.56.
Another pond, about 100m
x 25m, with only a Rivaldi valve cost about US$680.
An interesting fact about fish pond construction is that
whether the
pond is large or small, expensive or inexpensive, ponds are
all very
much the same. A
larger, more expensive pond will not necessarily be
a better pond.
Here is an example of a good beginning for a new and small
fish farmer:
A
"backyard" fish pond was planned and sited very carefully
by a farmer.
The pond was dug by the farmer and
constructed
with bamboo
pipes for water inlets and outlets. The
construction
itself cost no
money. The farmer's only expense was a
supply of
fingerlings purchased from a nearby market.
This
fish pond,
managed by the farmer and his family, produced
enough fish for
the family and some extra income from fish
sold or bartered
for goods needed by the farmer. The
family
ate well and
suffered no major illnesses during the year.
Next year, the farmer plans to add another
pond and to produce
more fish for
market. He will add a Rivaldi valve or
a wooden
monk to this new
pond, because either of these will make ongoing
management
somewhat easier, now that there will be two
ponds to manage
(The bamboo pipe sometimes got clogged.
This
was no problemn
to correct when there was only one pond.
But
it would take up
needed time in a two-pond operation).
Whichever the
farmer chooses, the valve or the monk, he will
make it himself
with materials found locally, using money from
the sale of his
fish.
This farmer
began his operation well. He started
small and
worked into a
larger operation. However, even for the
larger
fish farm, he
planned an expansion which was within his means.
This kind of
careful planning increases the farmer's chances of
success -- and
yours. And the scope of the project is
something
he can undertake
on his own. He gained the knowledge and
experience that he needs to expand his
operation.
The following section presents a range of ideas for
constructing fish
ponds. The farmer
can pick a combination of construction possibilities
which best fit his own needs and resources.
IMPORTANT: Stress
that the "right" way in any situation is the way
which:
*
the owner can afford
*
the owner can manage easily
*
fits the owner's needs most completely
Construction should begin only after careful planning such
as that
outlined in the preceding sections on "Planning."
<FIGURE>
12p54.gif (437x437)
A fish pond has three main parts:
the walls, the water inlet, and the
drainage system.
Walls are also called dams, dikes, levees, or bunds.
This manual uses "walls."
Whatever they are called, walls hold the
water
in the pond. They
can be built using soil taken from inside the pond,
or they can be built with soil taken from another
place. They must be
strong enough to withstand the pressure of all the water
inside the pond:
water constantly pushes against the walls.
They must also be water-tight
(impermeable), so the pond does not leak.
The water inlet, located above the pond water level, is used
to let water
into the pond and is closed off after the pond is filled.
The drainage system is used to empty the water from the pond
when the
farmer is ready to harvest the fish.
There are many ways of making inlet and drainage
systems: the most
important criterion is that they work.
But the walls are especially
important: they are
all that keep the fish inside the pond.
The walls
must be built carefully.
Pond construction follows the same principles whether the
pond is a
single backyard pond or part of a large fish hatchery.
These are the
steps in pond construction:
*
Survey the land
*
Mark out the area of the pond
*
Measure and mark out the walls
*
Excavate the pond bottom, if necessary
*
Build the drainage system
*
Build the water inlet
*
Build the walls
*
Seal the pond bottom and walls
Each of these steps
will be discussed in detail in the following pages.
Survey the Land
The first step in the construction of a fish pond is marking
the area of
the proposed pond.
If the site chosen is a natural slope, the first
thing to be done is to find out where the main wall will be
built. The
main wall should be marked off at the lower end of the pond,
where the
pond will be the deepest and the slope the greatest.
This is where the
pond's drainage system will be put.
If the pond is to be on a flat area,
the pond bottom itself must be made with a slope so the pond
will drain.
This is done by digging one end deeper than the other
end. Remember:
the main wall is always at the deeper end.
DETERMINING THE SLOPE
Even flat ground usually has some kind of slope, although it
may be very
little and hard to see.
So, before constructing the pond, the land is
surveyed to find out which way the land slopes and what that
slope is.
There are a number of ways which can be used to determine
slope. The
way outlined here probably would not be used by many farmers
if they
were building a pond on their own, but this is an accurate
method of
determining slope and should be encouraged if at all
possible.
<FIGURE>
12p56a.gif (393x393)
To survey the land for slope, some
stakes (long, straight pieces of
wood), some string (fishline, etc.),
and a carpenter's level are needed.
Most farmers will not be familiar
with the level, a device that has
an air bubble trapped inside which
rests between two drawn lines.
When the level is placed on the
ground, it shows whether the area
is flat or sloped:
if it is straight
or flat (level), the bubble stays
in the middle between the lines;
if the land slopes, the bubble will
move to the right or left of the
lines, depending upon the direction
of the slope.
<FIGURE>
12p56b.gif (108x437)
Farmers who cannot find a carpenter's
level can make a level by getting a
small lightweight container.
They
should then place the container on a
known horizontal surface, add water,
and draw a line around the inside of
the container at the water level.
Then, if this container is placed on
a slope, the water will shift away
from the line to show the slope.
<FIGURE>
12p56c.gif (285x285)
When all the equipment is gathered, measure the slope.
*
Look at the land and decide which part is
higher.
*
Drive a stake or a piece of wood or bamboo
into the ground
at the highest
point.
*
Walk away downhill from the stake about
100cm. Drive another
stake into the
ground at this point.
*
Tie string or fishline or vine (whatever is
being used)
between the two
stakes. Attach the level to the string.
Then move the
string up and down on the stakes until the
bubble is
between the lines on the level, or the water
level is even
with the line marked on the container.
This will mean the string is level
between the stakes,
even though the
stakes are in the ground at different
heights.
*
Measure the height of each string by
measuring from ground
level to the
place where the string is tied.
<FIGURE>
12p57.gif (388x388)
This drawing shows that one string is tied at 20cm; the
other is tied at
25cm. Therefore, one
end of the area is 5cm lower than the other.
The
distance covered by the string is 100cm, so the slope is 5%
(over 100cm
of ground, the elevation changed 5cm).
Since a slope of 2-5% is good for
a fish pond, this site has a satisfactory slope for a pond.
Other Ways of Determining Slope.
As mentioned earlier, the above method
of measuring slope is a good one, but it my be difficult for
some people
to do. It is
possible to calculate slope roughly. A
farmer, who realizes
that what he is looking for is a way to place his pond so
that the water
can enter from the water source and drain away well, can
figure the slope
of his land by doing such things as rolling a ball or other
round object
and watching carefully to note where and how quickly the
ball rolls. A
good slope would mean a slow-rolling ball.
A variation of this involves
throwing a quantity of water, or a mixture of water and dye,
on the ground
and watching the path it takes and its speed as it moves
along the ground.
It is important to consider slope carefully.
A well-placed pond with
good drainage is easier to care for and has more chance to
be successful.
It may be necessary for the pond owner to measure his land
only once to
find a good location.
Or it may be necessary to repeat the measuring a
number of times.
This is probably a good thing to encourage since
locations which look alike to the eye often have enough
difference in
slope to make a big difference to a fish pond.
Also, determining slope
is a larger project if more than one pond is being
built. Then the Ponds
must be laid out in relation to each other.
There may be several areas which have the correct slope, but
only one
which is good in terms of getting the water into the pond
from the water
source and out of the pond easily.
For example, the farmer might like
to drain his pond so that the water irrigates his
fields. Therefore, he
will want to keep this in mind when he decides upon the
exact placement
of his pond.
Likewise, if he is building a pond on a hillside in back
of his house, the slope may be perfect, but he will need to
avoid drainage
into his buildings.
Once the slope is found, the location of the main wall can
be determined.
Of course, if the pond is built on flat ground, it will have
four walls.
If the pond is a barrage pond, it may only have one
wall. The number of
walls depends upon the land.
The shape of the land may mean that one
wall or two walls or four walls will be needed.
Mark out the Pond Site;
Measure, the Walls
Now that the slope is known, the place of the main wall is
known. The
main wall is at the end of the pond which will be deepest,
and is the
wall where the drainage system will go.
Mark out the main wall, and any other walls that will be
built, with
stakes. The walls,
when finished, will be wide: it does
not matter so
much where the stakes are placed within the width of the
planned walls,
for they are to be used as height markers.
<FIGURE>
12p58.gif (344x344)
The farmer has to plan the depth of his pond and the height
of his wall.
If the pond is going to be 2m deep at the deepest end, for
example, the
walls should always be at least 30cm higher than the water
level for a
small pond, and at least 50cm higher for a large pond.
Also, the walls
will settle after they are finished, so it is best to make
the wall 10%
higher than the desired final height of the wall.
A 2m deep pond, therefore,
would have walls with a total height at the deepest point of
2.5 or
2.6m [height of wall before it settles = depth of pond +
30cm (for small
pond) or 50cm (for large pond) + 10% of depth and 30 or
50cm].
Tie strings to the stakes along the main wall line, at a
height of 2.5
or 2.6m for a pond whose deepest end will be 2m.
Use a levelling device
to connect strings to the stakes marking the other walls, if
the pond has
other walls, at the same level as the string marking the
height of the
main wall. The
strings are the building markers. When
the walls reach
the strings, they are the right height.
Dig the Pond Bottom
As stated before, the pond bottom must slope downward from
the shallow
end to the deep end to help drainage.
The pond bottom usually has a
slope of from 2 to 5%.
(A slope of 2% would mean that for every 100cm
change in length there is a 2cm change in height.)
<FIGURE>
12p59.gif (393x393)
The pond bottom must be clear of rocks, roots, trees, and
stumps so that
later, when a net is used to harvest the fish, the net will
not get caught
and tear. If the
pond bottom is already smooth and slopes well, it can
be left alone. Or,
if the pond bottom only has grass on it, the grass
does not need to be removed before the pond is filled.
In fact, once
water is added to the pond, the grass will die and rot and
add nutrients
to the water.
If the pond bottom does not already slope downward, excavate
(dig out)
the bottom area of the pond until a good slope for drainage
is made.
Adjust the height of the strings tied to the wall markers if
digging the
bottom has changed the height.
Keep the soil which was dug out of the pond:
when the pond walls are
finished, the soil can be placed on top and planted with
grass. This
fertile topsoil will root grass easily; this grass will help
keep the
walls from eroding (washing away).
<FIGURE>
12p60a.gif (317x317)
The pond bottom can be excavated by hand
or by using machines, like bulldozers,
if they are available.
Remember: if the
land for the pond is chosen well with regard
to the natural topography, only a small
part of the pond bottom will need to be
dug out. The most
important thing is
to have the pond bottom slope so that
the pond can be drained.
Build a Drainage System
A drainage system is anything that is used to empty the
pond. It consists
of the outlet system for letting water out of the pond and
the drainage
ditches which carry the water from the pond away.
As stated before, the best and easiest way to have a good
drainage
system is to build the pond in a place which provides a good
slope -- on
a hill, for example.
This is the first step. Then,
there are many
different drainage systems which can be put into the
pond. Some of these
drainage methods are expensive; others are very inexpensive.
The drainage system must be built before the pond walls
because some
drainage devices go through the walls.
(In some countries the drainage
is done by knocking a hole in the wall of the pond.
When the pond is
dry and empty, the hole is patched up.)
<FIGURE>
12p60b.gif (486x486)
One of the easiest ways to drain the pond is to place a
bamboo or plastic
pipe through the base of the wall into the middle of the
pond. The end
of the pipe which is inside the pond has a screen over it to
keep fish
from entering the pipe.
The other end of the pipe, the end that is
outside the pond, is plugged with wood or clay.
To drain the pond at
harvest time, the plug is pulled out.
Two other methods of draining the pond which work but are
not used as
often, are the siphon and the pump.
A siphon is merely a flexible
plastic or rubber tube.
One end of the tube is in the pond near the
bottom; the other end is placed on the ground outside the
pond. A
vacuum is produced in the pipe by sucking at the end outside
the pond
until water begins to flow out.
The end of the pipe inside the pond
must be kept in the water or the siphon will not work.
<FIGURE>
12p61.gif (317x437)
The pump is usually not a good idea for a farmer because the
engines
that are used to run the pumps are costly and often not
available, or
gasoline to run them is costly, or they must be given
frequent attention
so they will not break down.
All ponds must be drained for harvesting fish.
Also, it is a good idea
to let a pond dry out completely once every year or so to
get rid of any
unwanted fish and/or disease-causing organisms.
The following are some tested, effective drainage systems a
farmer can
consider for his pond.
RIVALDI VALVE This
valve was named after a farmer in Paraguay who
first used the system.
It is an easy and good method to use in a small
fish pond. A farmer
who is building only one small pond for family use
would find this valve a good choice for his needs.
The Rivaldi valve is a flexible plastic pipe.
Place the pipe on the
ground before the wall is built.
Build the wall. Then turn
up and tie
the pipe to a stake.
Tie the pipe end at a level which is somewhat above
the usual level of the water in the pond.
Keep the pipe up and tied to
the stake until it is time to drain the pond.
Then, untie the pipe and
let it lie on the floor of the pond until the water is out
of the pond.
At other times, the pipe works as an overflow to let out
water after a
heavy rain: when the
water level in the pond reaches the top of the pipe,
water will flow down the pipe and out of the pond.
The Rivaldi valve should have a screen over the end inside
the pond to
keep fish from going out of the pond while the pond is being
emptied or
drained.
<FIGURE>
12p62a.gif (437x437)
ELBOW JOINT A
variation of the Rivaldi valve, this consists of two
metal or plastic pipes connected by an elbow joint.
The joint lets the
upper pipe be turned down to drain the pond.
The joint is screwed onto
the ends of the two pipes, one of which extends under the
wall and the
other above the surface of the water.
This drainage method is also
called a "turn-down" pipe because it is actually
turned on its side to
drain the pond.
<FIGURE>
12p62b.gif (437x437)
BOTTOM-WATER OVERFLOW
This drain takes water directly from the
bottom of the pond where oxygen levels are the lowest.
The Rivaldi valve
and elbow joint do this also, but each of these requires
that the pipe
be lowered so the pond can be drained.
The bottom-water overflow regulates
the depth of water without any need for moving the
pipes. When.
new water is added to the pond, the less-oxygenated water at
the bottom
drains out automatically.
This type of drain is relatively complicated and usually
difficult to
build. For a small
fish farm operation, it would probably not be worth
the effort.
<FIGURE>
12p63a.gif (437x437)
DOUBLE SLEEVE OVERFLOW
This drainage system is built like
the turn-down pipe, except a large pipe is placed over the
section of
pipe which extends above the pond's surface.
This outer pipe should be
longer and wider than the inner pipe, which is placed so
that it is about
equal in height to the depth of water desired in the pond.
When fresh water is required in the pond quickly because the
water is
too warm for the fish or because the oxygen levels are low,
all the
farmer has to do is to add water to the pond.
The double-sleeve overflow
automatically drains the stale water from the bottom of the
pond.
<FIGURE>
12p63b.gif (437x437)
SLUICE A sluice can function
in a number of ways in a pond. It can
be
a screened gate in a water channel going into the pond, or a
drainage
gate leading water out of the pond.
In a pond, a drainage sluice gate is anchored into the main
wall by
extending the sides of the sluice into the wall so the
sluice structure
stands upright. The
sluice is constructed at the center of the main wall
before the dike is built.
<FIGURE>
12p64a.gif (353x353)
The sluice can be made of wood, cement, or brick.
It can have one or two
wooden gates which are removed to empty or fill the
pond. A sluice also
can have a screen gate to keep unwanted fish from entering
at an inlet
and pond fish from leaving at the outlet.
<FIGURE>
12p64b.gif (393x393)
IMPORTANT: The
wooden gates of the sluice must fit into the slots well,
but easily. The wood
will swell to make a tighter seal as it is soaked
by the water in the pond.
The slots (grooves) can be filled with several
strong, long, narrow boards which have been bevelled or
notched so that
they fit together tightly.
Or the slots can be filled with single pieces
of wood. When single
pieces of wood (or a number of boards which have
been fastened tightly together) are used in a sluice, the
pond is drained
and the water flow regulated by lifting the entire wooden
structure out
of the groove to a height which allows some or a lot of
water to flow out
of the pond. When
separate boards are used in the grooves, the boards
are taken out one at a time.
If a small flow out of the pond is desired,
only one board may be taken out.
To drain the pond, all the boards are
removed. In a sluice
having two wooden gates, the space between the gates
can be packed tightly with earth.
This will help seal the water into
the pond.
<FIGURE>
12p65a.gif (393x393)
MONK The monk is
very much like the sluice, but it is not built into
the pond wall the way the sluice is.
Sometimes the back of the monk
does touch the wall, but it is not built into the wall.
Also, a monk is
never used at the inlet as a sluice can be.
<FIGURE>
12p65b.gif (437x437)
<FIGURE>
12p66.gif (393x393)
A monk-type drainage system controls the level of water and
prevents fish
from escaping when the pond is being filled.
It also allows for good
drainage of the pond.
The completed structure consists of a horizontal
drainage pipe and the vertical structure, or monk.
The drainage pipe
must be placed before the walls are built; the monk may be
built outside
the pond, and placed inside later.
The drainage pipe runs from the back of the monk under the
pond wall.
It should be between 20 and 40cm in diameter; if piping of
this diameter
is not available, two pipes may be used.
For good drainage, place the
pipes 30 to 40cm lower than the pond bottom.
Make sure the drainage pipe
is on solid ground so that the pipes do not bend.
Bent pipes are difficult
to clean out when clogged.
The monk itself is a structure which is closed on three
sides and open
in the front. The
open side should face the inside of the pond and should
be at least 30cm wide; the entire monk should be at least
40cm above the
surface of the water.
The two parallel sides of the monk, and the bottom, have
grooves cut in
them: a monk may
have two or three grooves. One groove,
or part of a
groove is always for the screen.
The other groove(s) is for the boards.
Monks can be made of wood, concrete or brick.
A wooden monk should use
strong wood -- 4 to 5cm thick.
A concrete monk
should be reinforced with metal. Before
the concrete is
poured, a wooden form shaped like the monk is made and
oiled. A frame,
slightly smaller than the wooden form, is made of chicken
wire, or some
other strong wire, and set down inside of the wooden
form. The concrete
is then poured into the form.
A good concrete mixture for monks is
1 part cement, 2 parts clean sand, and 4 parts crushed
stone, by volume.
<FIGURE>
12p67.gif (600x600)
If the monk is made of
concrete, the grooves can
be shaped by bending iron
rods into a "U" shape.
Remember, the grooves must
be sunk into the sides and
bottom of the monk.
<FIGURE>
12p68.gif (486x486)
The grooves are filled by
using a series of boards -- wide
enough to fit the
grooves well and between
20 and 30cm high.
Each
board has a hook on it so
it can be lifted from the
groove easily; the boards
may also be bevelled or
notched so that they fit
together well.
If the monk has three grooves, the first groove can be a
large screen.
The screen is what keeps the fish from escaping as the pond
drains.
However, if the monk has only two grooves, a smaller screen
can be placed
above or below the boards in the first groove.
Placing the screen at
the bottom allows water to drain out from the bottom of the
pond.
HERRGUTH MONK This
is a monk with three grooves. A large
screen
is in the first groove.
The large screen is better than a smaller one
because it does not get clogged up as easily as a small
screen.
The second groove holds a series of boards.
The lowest board can be a
small screen. Water
flows through the large screen in the first groove,
and through the small screen in the bottom of the first
series of boards,
up and over the third series of boards into the drainage
system.
<FIGURE>
12p68.gif (437x437)
There are other ways this kind of monk can be built.
For example, the
second groove could be filled by a large wooden gate (one
piece of wood
or several fastened together) which could be raised and held
up to allow
a flow of water from the bottom of the pond.
It is this flow of water
from the bottom of the pond which is important.
The Herrguth monk would probably not be used in a pond which
is filled
by rainwater. In
these ponds -- sky ponds -- a regular monk is used,
and the space between the two wooden gates is packed with
mud to make
a watertight seal which lasts for the fish-growing season
and is removed
when the pond is drained for harvest.
SOME NOTES ABOUT MONKS
Be careful with screens. Bamboo
slats
can be used instead of screening if the fish are large.
But for fry,
the holes should be less than 2mm in diameter.
Often the screens are
made by poking small holes in sheet metal.
The screen mesh can get
larger as the fish grow.
A valve is sometimes placed on the drainage pipe behind the
upright part
of the monk. This is
used to control the draining speed and is easier
to do than to move the boards in the grooves.
A large catching ditch can be made in front of the monk to
help with
taking fish out of the pond when the pond is being drained
for harvest.
DRAINAGE DITCHES
Drainage ditches are channels which should be dug
on the bottom of the pond to help the water flow out.
Lining the ditches
with stones helps the water flow.
A small family pond does not require
this system of drains.
The only real requirement for drainage is a
gentle slope.
This is the time to build other ditches which may be
needed. For example,
if the farmer wants to use the water from his fish pond to
irrigate
his land, he will want to construct the ditches or channels
which will
carry the water from the pond to the field or to storage
tanks for use
later. Therefore,
the farmer must consider carefully where the water
which is draining from a pond is going to go.
If the pond is being fully
drained, and the pond is built on flat ground, he should
build drainage
ditches around the outside of his pond to drain the water
away from the
walls. These ditches
should be 30-40cm deep.
<FIGURE>
12p69.gif (486x486)
Water Inlet
All ponds, except for those filled directly by a spring or by
rainwater,
need water inlets.
The water inlet must be constructed so that it supplies
adequate quantities and quality of water, and so that it
does not allow
unwanted fish or other materials to enter the pond.
This usually means
there must be a channel of some kind to bring the water to
the pond from
the source and a filter of some kind to keep the water which
goes into
the pond clean and free from predators.
<FIGURE>
12p70.gif (486x486)
A water inlet can be as simple as a bamboo pipe of good
diameter running
from a water source through the wall into the pond.
Remember:
the inlet
pipe should be placed above the water level so that incoming
water drops
into the pond. In
some areas, such things as bamboo strips are tied to
the end of the inlet pipe which is placed over the
pond. The water flow
into the pond is broken up by the strips and the water picks
up and takes
more oxygen from the air into the pond water.
If the pond is large or is a stream-fed barrage pond, a
sluice makes a
very good water inlet.
The sluice can be one piece which controls flow
when it is lifted to various heights, or the sluice can be a
series of
boards slipped in and out of the grooves.
It is better to filter most pond water as it goes into the
pond. Filters
are not needed if the water is clean and clear and the
farmer knows the
source is free from unwanted fish.
But if the water is muddy, or has
lots of leaves or debris in it, a filter helps keep the
water quality
good.
A filter can be placed at the beginning, middle or end of
the channel
which brings water to the pond.
Usually filters work best near the water
inlet. Filters can
be made very simply. Remember they must
keep unwanted
fish out and pond fish in.
A wire screen makes a good filter.
The picture above shows a sluice with
a gate with fine screening to strain incoming water of
pieces of debris
and other unwanted fish and materials.
Note the screen fits into the
water channel exactly.
<FIGURE>
12p71a.gif (393x393)
The horizontal screen at the
left is very effective.
Here the screen is placed
so that the water passes
through as it falls into the
pond. This screen
merely
juts out from the wall at
the inlet.
In the version below the
horizontal screen has a
vertical screen wall attached
to it. This short
wall
prevents fish from going
over the screen.
<FIGURE>
12p71b.gif (437x437)
In any variations of these kinds of filters, the screens
should be
assembled into one piece for easy removal as a
unit for cleaning.
There are other ways of filtering the water:
A nylon mesh bag makes a good filter, as long as it is
partially submerged
in the pond so that it does not tear as the bag catches fish
or
other material from the water source.
Check it periodically.
<FIGURE>
12p72a.gif (437x437)
A sand and gravel filter is particularly useful for cleaning
out fish
and eggs. It
requires building a smaller pond or tank at the water
inlet. If a filter
is built in the earth it must be lined with a waterproof
liner.
<FIGURE>
12p72b.gif (486x486)
A saran fiber filter is basically like a wire screen that is
placed
horizontally underneath the water inlet.
However, it is placed in a
box standing in the water and uses saran fiber material
instead of wire.
(See drawings next page.)
<FIGURE>
12p73.gif (540x540)
These filters all have good and bad points.
All must be cleaned often
to remove debris that collects in them from the water
source. The best
filters are the sand and gravel filter, and the saran
filter, but these
are more costly than the others.
The farmer should examine his water source carefully before
deciding on
the kind of filter.
If the water is very muddy, or has lots of leaves
and grass in it (organic matter), he can use the wire
screen. If the
water source is free of organic material, the mesh bag will
work because
it is not likely to be torn.
If the water contains unwanted fish and
eggs, as well as a lot of organic matter, the saran filter
or the sand
and gravel filter is best.
To clean the filters, remove them and clean them with a
brush and fresh
water. Or flush the
filter with water in the opposite direction of the
normal water flow.
This is called backwashing.
IMPORTANT: Filters
must be kept clean to be of any use.
These filters
should be cleaned each time water is let into the pond.
SILTATION TANK One
other structure which should be built at the
water inlet, when necessary, is called a siltation
tank. Silt is the
mud that is suspended (floating) in water.
Silt can become a problem
when it clogs the gills of the pond fish so they cannot
breathe. If
the water source has a lot of mud in it, a siltation tank
should be
built at the inlet to the pond, or at the inlet to the first
pond, if
it is one of a series.
The siltation tank can simply be a smaller pond.
The water flows into
this pond and is kept there until the mud falls out of the
water and
settles on the bottom.
Then the clear water is let into the fish pond.
Siltation could also be done in a storage tank made out of
old oil drums,
etc. The important
thing is that something be constructed or set up so
that the silt has a chance to fall out of the water before
that water
goes into the pond.
The silt must be removed from the siltation tank or pond
every so often.
The silt which is removed should be used in gardens and
fields: it is
very fertile.
<FIGURE>
12p74.gif (437x437)
Build the Walls
The walls (dikes, dams, levees) have to withstand the
pressure of all the
water in the pond.
They also have to be watertight to keep the water
inside the pond.
The construction of the walls depends upon the kind of soil
in which the
pond is being built.
A soil which is a mixture of sand and clay is best.
If pure clay is to
be used, it must be mixed with other soil before it can be
used. Pure
clay will crack and leak.
Do not use turf, humus, or peaty earth.
All
stones, pieces of wood, and other materials which might rot
or otherwise
weaken the wall must be removed before building begins.
If the soil
contains enough clay, the walls can be built by placing
layers of soil
20cm deep over the drainage pipes and tamping each layer
down until it
is compact.
<FIGURE>
12p75a.gif (437x437)
The finished height of the wall should be about 30cm above
water for
small ponds and 50cm above water for large ponds.
The width of the wall
at the top should be about equal to its height.
For a large pond, the
wall is never less than 1m wide at the top; most walls are
built so that
two people can walk side by side along the top.
Tamp the soil down with a simple tamping tool.
Some people use a large
rock or even their own weight by jumping up and down on the
soil. The
important thing is that the soil must be packed down very
tightly.
<FIGURE>
12p75b.gif (353x353)
One way to build pond walls in soil that does not have a lot
of clay or
is very sandy is to build a "key."
The key is made of clay soil (it can
be pure clay) and adds strength to the walls.
To make a key, dig a
trench (or shallow hole) about 1m deep and 1m wide in the
center of the
places where the walls will be.
Then bring clay soil and pack it tightly
into the trench.
Also put a thick layer of clay soil on the pond bottom
and pack that down tightly.
The clay layer on the bottom and the key
run together as shown.
This connection of the bottom and the key helps
prevent leaking. The
drainage pipe should be placed in the clay lining.
<FIGURE>
12p76a.gif (393x393)
If the farmer has a soil which is a mixture of clay and
sand, and he is
not sure it is strong enough, he may still wish to build a
clay key. Or
he can build a key using the same soil used in the wall.
This key must
be packed down very tightly.
<FIGURE>
12p76b.gif (437x437)
The type of soil determines the ways in which the pond can
be prepared
so water does not leak out (see "Seal the Pond
Bottom", next page).
<FIGURE>
12p76c.gif (437x437)
The soil also determines the slope of the walls.
Soil with a lot of
clay in it can have a greater slope on the outside wall than
on the inside
wall. A typical wall
is built with an outside slope of 1:1 and an
inside slope of 1:2.
A slope of 1:2 means that for every change in
length of 2m there is a change of 1m in height.
Once the walls are constructed, the farmer should plant
grass on them.
The grass roots help to hold the wall together and prevent
erosion of
the soil. However,
NEVER plant trees on the wall. As the
tree roots
grow they will crack and destroy the wall.
Seal the Pond Bottom
The last step in pond construction is sealing the pond
bottom so that
it does not leak. If
the soil has a lot of clay in it, no special sealing
is needed. If the
bottom is sand or gravel, it should be sealed to help
it hold water. One
way to seal the pond is to build a clay core into
the wall and extend the clay over the bottom of the pond as
a lining.
This kind of sealing must be done when the walls are
built. After the
walls are built, there are other methods you can use for
sealing the
pond.
<FIGURE>
12p77.gif (437x437)
A pond can be sealed using hollow cement blocks, but this is
expensive.
Another method of sealing the bottom calls for using a sheet
liner made
of polyethylene plastic, or a rubber liner.
The waterproof sheet is
placed on the pond bottom and around the sides in one piece
(the farmer
may have to tightly seal several sections together), then
covered with
soil.
Another technique, recently developed in the USSR, is called
a "gley" or
"biological plastic."
"Gley" can be made in the pond in this way:
*
Clear the pond bottom of debris, rocks, and
all other materials.
*
Cover the pond bottom and sides completely
with animal manure.
Apply the
manure in an even layer.
*
Cover the animal manure layer with banana
leaves, cut grasses, or
any vegetable
matter. Make sure that all of the
manure is covered.
*
Put a layer of soil on top of the vegetable
layer.
*
Tamp the layers down very well.
*
Wait 2 to 3 weeks before filling the
pond.
5 Preparing
the Pond
The last pages of the construction section presented several
ways of
sealing the bottom of the pond so it will hold water
better. This
section tells what has to be done to prepare the completed
pond for
the fish.
Conditioning the Pond
If the pond is an old one from which the fish have been
harvested, plow
it completely.
Plowing turns the ground over so that it dries well.
Clear the bottom of any twigs, stumps, branches, or dead
fish. Any predators
(snakes, frogs, etc.) must be taken out by hand or poisoned
(see
"Problems of Fish in Pond" for more information on
this subject). Then
smooth the bottom out again.
When the pond is dried enough, the soil
will have large cracks in it.
After the pond is plowed, cleared, and smoothed, it should
be conditioned
with lime.
<FIGURE>
12p79.gif (285x285)
Whether the pond is old or new, a
layer of lime should be placed on
the bottom of the pond.
Place the
lime on the pond two weeks before
the water is put into the pond.
Lime conditions the soil of the pond.
It is not a fertilizer, but it helps fertilizers work.
It is especially
important to use lime if the soil has acids in it which
might harm the
fish. Lime can
control these acids so they are not a danger.
A farmer
who is not sure whether the soil of his new fish pond has
acids in it --
because he had no place to get his soil tested, or because
he has never
farmed the land -- is always safer if he puts lime on the
bottom of the
pond.
Lime comes in several forms:
ground limestone; agricultural lime;
hydrated (builders') lime; or quicklime.
Of all these types, hydrated
lime is cheapest to use because it is more concentrated.
Quicklime must be used carefully:
it can burn if it touches the skin
and is harmful if breathed into the body.
Farmers should be warned to
use quicklime only with extreme care.
Lime should be put on the pond bottom at the following rates
for a new
pond:
Ground
Limestone 1140kg per hectare
Agricultural Lime 2270kg
per hectare
Hydrated
Lime 114kg per hectare
Quicklime 200kg
per hectare
A word about limestone:
In many areas of the world, limestone can be
found locally. It is
a soft stone and may be ground by the farmers
themselves. It is a
good idea to let farmers know whether or not limestone
is available locally and to help them identify it if they
can not
already do so.
Filling the Pond
After the lime has been on the pond bottom for at least two
weeks, let
the water in slowly.
The water should fall from the water inlet into
the pond below, so that the water mixes with oxygen from the
air as it
falls into the pond.
<FIGURE>
12p80.gif (285x285)
The water should not go in too quickly.
If the water goes in too fast,
the pond bottom will get stirred up and make the water
muddy.
Let the pond sit for a few days after it has been
filled. Then check the
quality of the water in the pond -- before adding the fish.
Fish growth depends greatly on the quality of the water used
in the pond.
And the quality of the water depends upon where it comes
from and what
kind of soil it travels over.
Testing the water quality means making
sure that all the factors which relate to water are right
for the fish.
These factors are:
temperature, oxygen content, pH, turbidity, hardness,
alkalinity, and nutrient availability (source of food for
the fish). The
farmer does not need to know these particular words to raise
fish well,
but he does require a working knowledge of the factors that
are part of
the water world in which the fish live.
TEMPERATURE
Fish are cold-blooded animals; that is, their body
temperatures depend
upon the temperature of the water in which they live.
Every fish species
has a temperature range within which it grows quickly.
This is called
the optimum temperature range, and it means that this fish
grows best
at temperatures within that range.
In a fish pond, the fish should live
at their optimum to grow well.
However, since fish have different
temperature requirements, the farmer must choose the fish
which will
grow best in the temperature range of his pond.
Here are some of the common pond fish and their temperature
ranges:
Genus,
species Common name
Temperature [degree C]
Tilapia mossambica
tilapia 25-35
Osphronemus goramy
gourami 24-28
Puntius javanicus
tawes 25-33
Cyprinus Carpio
common carp
20-25
Ctenopharyngodon idellus
grass carp 25-30
Anguilla japonica
eel 20-28
This chart shows that all the fish on this list could live
in water that
is 25 [degrees] C (77 [degrees] F).
The chart also shows that an eel can live
and grow well
at 20 [degrees] C, but that the tilapia and the grass carp
will not do well at 20 [degrees C]
because this temperature is below the range in which they
are comfortable.
When the temperature goes higher or lower than this optimum,
fish will
not grow.
Eventually, if the temperature goes too high or too low,
the fish will die.
The farmer must watch the temperature in the pond water
carefully,
especially if the weather becomes unusually hot or
cold. If it is
possible, it is a good idea for a farmer to use a
thermometer to find
the temperature of his pond water.
This can be done by using a
thermometer which is used for taking temperatures when
people are sick.
The most important step is to guide the farmer to stock fish
which will
do well in the normal temperature ranges of his area.
Then the temperature
of the water will not generally be a problem, except in
cases of
unusual weather.
<FIGURE>
12p82a.gif (230x230)
Some experienced fish growers can judge the water
temperature by putting
their arms in the water.
Most people cannot tell temperature this way.
But if the right kind of fish has been chosen for the pond,
the farmer
need only watch the fish to be able to judge the temperature
of the pond
water. If the water
is becoming too hot, the fish will not eat and will
move very slowly.
If the farmer sees this behavior in his fish pond, he can
take out some
of the pond water and put in new, cooler water.
Another way of protecting
the water from getting too hot is to find a way to shade the
pond,
so that the sun does not shine directly on the water.
The shading should
be temporary because sunlight is important to the success of
the pond.
<FIGURE>
12p82b.gif (437x437)
The picture on the previous page shows a fish pond being
shaded by
palm tree branches stuck into the ground around the edges of
the pond.
As soon as the temperature of the water goes down, the
branches are
removed.
Temperature, however, usually does not act alone.
If the fish are
showing signs of distress because of hot weather, it is often
a problem
caused by high temperatures and low oxygen content.
OXYGEN
The farmer cannot see oxygen, so it may be hard for him to
realize
its importance. But
it is worth taking the time to help a pond owner
understand oxygen as a critical factor in the success of his
fish pond.
Oxygen lack is a problem which can occur at any time during
fish pond
operation, and there is a good chance the farmer will have
to depend
only upon his own knowledge of the problem and its cause to
solve it
immediately.
Fish, like all animals and human beings, need oxygen to
breathe and,
therefore, to live.
Through a process called respiration, fish and
human beings take in oxygen and give off carbon
dioxide. Fish will not
grow well when the oxygen supply is low; and if the oxygen
level gets
too low, they will die.
Oxygen is a gas.
Human beings get the oxygen they need from the air.
They cannot see it, or smell it, but without it they would
die. Most
fish can only get oxygen from the water in the fish
pond. The farmer
cannot see the oxygen in the water either, but he should
realize that
it must be there in sufficient quantity for the fish to
live.
Oxygen troubles arise in a pond when the supply of oxygen is
used up
faster than oxygen is put into the pond.
This happens to human beings
too -- if too many people are shut into a room with no
windows or airholes,
the respiration of all these people uses up the oxygen.
Soon,
there is too much carbon dioxide in the air.
The people have trouble
breathing until a window is opened and fresh air containing
oxygen is
let in.
This is exactly what happens to fish in the fish pond.
The fish are shut
up in the pond, and if there is not enough oxygen entering
the pond,
they will have trouble breathing.
And, if the problem continues, they
will die.
Water contains tiny plants and animals called plankton.
Most plankton
are so very small that they cannot be seen without using a
microscope.
The plants are phytoplankton:
The animals are zooplankton:
<FIGURE>
<FIGURE>
12p84a.gif (348x348)
12p84b.gif (393x393)
Water also contains higher orders of vegetation.
These plants are much
larger than the phytoplankton.
<FIGURE>
12p84c.gif (534x534)
The fish and the zooplankton use oxygen and give off carbon
dioxide in
respiration; the phytoplankton and higher plants use carbon
dioxide and
sunlight to produce oxygen during a process called
photosynthesis.
<FIGURE>
12p84d.gif (540x540)
The oxygen in a fish pond also is used up by the process of
decay.
Dead organic matter -- leaves, fish, other plant and animal
material
present in the pond, use up oxygen in the decay process
called
oxidation. Oxidation
and respiration go on both day and night, while
photosynthesis can take place only during sunlight hours.
Therefore, there are times during the day when the oxygen
levels in the
pond can be very low, and oxygen may have to be added to the
water.
Oxygen can be added to the pond water by taking out some of
the old
water which is low in oxygen and adding new water.
<FIGURE>
12p85a.gif (534x534)
The new water should be sprayed or bubbled into the pond so
that the
water picks up oxygen from the air as it falls into the
pond.
Oxygen also can be added to pond water by:
Stirring up the water already in the
pond. Some farmers
beat and stir the
water with poles.
<FIGURE>
12p85b.gif (393x393)
Some pond owners use oars to stir the water.
<FIGURE>
12p86a.gif (437x437)
Other owners run small motors
to bubble the water in the pond.
<FIGURE>
12p86b.gif (393x393)
In addition, winds which are strong enough to ripple the
surface of the
water in the pond help the air and water to mix.
Remember:
any disturbance
of the water made by man or by nature helps put oxygen into
(aerates)
the water.
Life under the water is a new idea to many farmers.
And it is sometimes
difficult to understand that the balances which exist on
land are also
present in the water.
Oxygen is produced and used both above and below
the surface of the water.
The fish pond does well only when oxygen
production and oxygen use are in balanced relationship.
If the farmer understands the balance --
how oxygen is added and how it is used
up, he will know how to watch for trouble
before it happens.
For example, if
the color of the water changes from green
to clear -- in a few hours or a day --
the phytoplankton are not producing
enough oxygen. If
the fish are at the
surface of the water and seem to
be gulping air, they may need oxygen.
Early in the morning, before
the sun comes up, or a long period
of no sunshine can be bad times because
the phytoplankton need the
sun to produce oxygen.
Long periods
of hot weather can create oxygen
problems because the pond water
gets warmer, and ways water cannot
hold as much oxygen as cool water
can.
<FIGURE>
12p87.gif (486x486)
The following table shows the difference in oxygen levels at
various
points in the day.
For example, at 6 am, the temperature has remained
steady, but the dissolved oxygen level has dropped to
6.3mg. At 6 pm,
after a sunny day, the dissolved oxygen level is 16.3mg.
This table also shows that on a typical day a pond's
temperature
does not vary greatly.
This illustrates why oxygen as a separate
factor is much more important than is temperature.
MEASURED
OXYGEN CONTENT COMPARED WITH TEMPERATURE IN ONE POND
Time of Day
Temperature [degree] C
Dissolved Oxygen, mg/1
2 am
29
9.8
6 am
29
6.3
10 am
29
6.7
2 pm
30
9.4
6 pm
29
16.3
10 pm
29
10.7
Oxygen is measured in either milligrams per liter (mg/l) or
parts per
million (ppm). One
milligram per liter of oxygen means that there is
one milligram of oxygen dissolved in one liter of
water. One part per
million is approximately equivalent to one milligram per
liter.
Fish begin to be stressed when the oxygen-level falls below
4mg/l. For
best growth, the oxygen levels should be above 5mg/l, but
not more than
15mg/l. Above this
level of oxygen, supersaturation often results
(too much oxygen).
Sometimes, if there is a lot of sun and a lot of wind
activity at the same
time, and if the temperature is low, the water can become
supersaturated
with oxygen.
Supersaturated water contains more oxygen than water can
normally hold at a given temperature; it is a temporary
condition. This
condition can place stress on the fish.
However, it does not happen
very often in small ponds because the wind is not usually
able to aerate
pond water as
thoroughly as it can in a large pond.
To determine the exact oxygen content
of a pond, certain chemicals and
equipment are needed.
Dissolved
oxygen is usually determined in
the laboratory by the Winkler
Method. Now,
however, there are
field kits available ((Hach, LaMotte).
These kits are, however, expensive,
and certainly will not be
available to most farmers.
<FIGURE>
12p88.gif (437x437)
pH, HARDNESS, AND ALKALINITY
These three factors are not the same thing -- each one is a
measure of
a certain characteristic or characteristics of the water in
a fish pond.
Each of these factors can be measured exactly if samples of
pond water
can be taken to a laboratory to be analyzed, or if chemicals
are
available for testing the water in the field.
Certainly if such
testing is possible, it should be done.
However, many pond owners are not able to get their water
tested and
they do not have the right chemicals and equipment to do the
tests
themselves. For
these people, it is best to stress the importance of
using lime in their ponds.
Lime is the proper treatment to correct
imbalances in these factors, each of which is discussed in
some detail
here.
pH. pH is the
measure of hydrogen ions ([H.sup.+]) in the water and is measured
on a scale of 1 to 14.
If the pH is between 0 and 7, the water is
considered to be acid.
If the pH is at 7, the water is neutral (not
acid or basic). A pH
of 7 to 14 means the water is basic.
Fish grow
best in a pH of between 6.5 and 9.0. Fish are very sensitive
to low
pH, or, in other words, to water which is acid.
Most pond fish will die
if the pH falls below 4 for a very long period of time.
Sometimes the pH of a pond can change quickly.
For example, a heavy
rain may carry acid from the soil in the dikes into the pond
water.
The best way to get the pH back to neutral is to add
limestone
(calcium carbonate) to the water by spreading it on the pond
bottom
or on the surface of the water.
A fish like tilapia can tolerate
pH from 3.7 to 10.5, but below a pH of 5, they are stressed
and they
will not eat.
Some people measure pH by tasting the water. If the water
tastes sour
or salty, it has too much acid in it.
Another way to find out pH is to
know where the water is coming from.
If the water comes from a swamp,
bog, or other place where the water is pretty stagnant and
contains a
lot of decaying material, it may be acid.
Most water, however, has a
pH which is very close to neutral.
If the water comes from a river or
lake, it is not likely to have a pH that will harm the fish.
If the
local fish do well in the water, the pond fish probably will
do well
also.
Litmus Paper. Some
farm owners find out their pH by using litmus paper,
or pH paper. These
are thin strips of paper which have chemicals on
them so that they change color when they are placed into the
water. If
the water is acid, the paper will turn one color; if the
water is basic,
the paper turns a different color.
The color on the paper is compared
to a color chart which will give the pH for that color.
There are also
electronic meters which measure pH, but these are expensive
and not
necessary in a field situation.
Hardness. Hardness
is the measure of total soluble salts that are
dissolved in the water.
These salts, usually calcium ([Ca.sup.++]) and
magnesium ([Mg.sup.++]), help the fish grow healthy bones
and teeth. Also,
the foods the fish eat, like the phytoplankton, need calcium
and
magnesium for growth.
Water that contains many salts is called "hard"
water; water that contains few salts is called
"soft" water.
Hardness is related to the pH of the water, but unlike the
pH, hardness
stays constant throughout the day.
Hardness can be measured in a laboratory
or by using a field kit with chemicals.
Hardness should be between
50 and 300ppm in the pond for best fish growth.
There are several ways a farmer can tell if he has very hard
water without
using chemicals. One
method is to look closely at the pond walls where
the water line is.
If there is a white line on the wall of the pond
where the water was touching the pond before the water level
fell, there
are salts present in the water which have dried on the pond
walls. This
water probably has a lot of salts.
Hardness is important to fish.
Another way a farmer can tell if the water is hard is to
wash his hands
with it at the side of the pond.
If the soap takes a long time to lather,
and if the lather does not stay very long, the water is
hard. If the
water is soft and does not contain many salts, it lathers
very easily and
is hard to wash off.
If the water is too soft, the farmer can increase the
hardness by adding
lime to the water.
Alkalinity.
Alkalinity is a measure of the acid-combining capacity of the
water; or it is also called its buffering ability.
Alkalinity measures the
amounts of carbonates and bicarbonates in the water.
These are materials
which mix with acid in the water.
The result of the mixing is that the
acid is not as strong.
Waters which have an alkalinity of 50 to 200ppm
are the most productive for fish.
Alkalinity, like pH and hardness, can
be corrected and controlled by adding lime to the pond.
The relationship
among alkalinity, hardness, and pH can be summarized like
this:
Low
Alkalinity = Low pH = Low Hardness
REMEMBER: THESE
THREE FACTORS ARE NOT THE SAME THING, BUT THEY ARE RELATED.
IN FISH
PONDS, ALL THREE CAN BE CONTROLLED BY ADDING
LIME TO
THE WATER.
TURBIDITY
Turbidity is the term for the suspended dirt and other
particles in water.
Turbidity can be a problem, especially in shallow ponds, if
the dirt and
particles prevent sunlight from reaching the plankton, so
that the phytoplankton
cannot produce oxygen.
An operating pond can be turbid if there
are bottom feeders such as common carp stirring up the
bottom mud. Or,
turbidity can result from a water source which has a lot of
silt in it.
Turbidity can be measured by just looking at the pond
water. Or turbidity
can be measured by using a device called the Secchi
disc. The Secchi
disc is also used to determine the total productivity of the
pond.
<FIGURE>
12p91a.gif (393x393)
A Secchi disc is about 30cm in diameter, painted white and
black or
just white, and has weights or heavy objects hanging on it
to make it
sink straight down into the water.
The disc is suspended on a rope or
a long piece of wire that is marked off in centimeters from
the disc up.
A Secchi disc can be made out of wood or metal -- as long as
it will
sink. The disc does
not have to be very complicated. It does not have
to be round, either.
It can be any shape, as long as it has some white
paint on it to help it be seen under the water.
The disc can be made
from a tin can pounded for this purpose.
<FIGURE>
12p91b.gif (437x437)
When the Secchi disc goes into
the water, it will sink straight
down and disappear from sight at
some depth. If the
disc disappears
at 30cm in depth, the pond is
turbid. If it disappears
immediately,
either it is very turbid
(brown in color), or it is very
fertile (productive), if green in
color.
Turbidity also can be measured without a disc, but this
requires somewhat
more experience. The
farmer stands in the pond and sticks his arm under
the water.
<FIGURE>
12p92.gif (317x317)
If his hand disappears when
the water is about elbow
deep, the water is not too
turbid. If it
disappears
before the water reaches the
elbow, the water is either
turbid or very productive.
If the entire arm from hand
to shoulder can be seen under
the water, it is not turbid
at all, nor is it very productive
(it does not contain
enough fish food).
One way to clear up muddy water is to scatter twelve bales
of hay per hectare
around the edges of the pond.
The hay will help to settle the mud
and can then be removed easily from the pond edges.
However, do not use
this method in very hot weather, because the hay will begin
to decay
very quickly and will begin to use up oxygen in the pond
water. If the
pond water continues to have a lot of silt in it, the farmer
should
consider adding a siltation tank (see
"Construction").
NUTRIENT AVAILABILITY
All fish require certain elements to grow and
reproduce. These essential
elements are:
carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium,
sulfur, calcium, iron, and magnesium.
Some other elements called trace
elements, are needed only in small amounts.
If these elements are missing,
or present in too small quantities, the fish will not grow
well.
Fish Require a Balanced Diet
of Elements
Carbon Potassuim
Hydrogen Sulfur
Oxygen Calcium
Nitrogen Iron
Phosphorus
Magnesium
Plus trace elements
Fish get these elements from the pond soil, the pond water,
and the
food they eat. Some
fish ponds lack elements that are necessary to
fish. In these
cases, it is necessary to add fertilizers to the water.
Fertilizers are simply materials which contain the missing
elements.
The elements most often missing, or in short supply in fish
ponds,
are nitrogen (N), phosphorus (P), and potassium (K).
<FIGURE>
12p93.gif (285x285)
Fertilizers containing these
missing elements are added
to the fish pond to help the
growth of the fish and of
the plankton the fish use
for food.
Fertilization
is discussed in the following
paragraphs.
Fertilizers
Fertilizers are materials added to the pond to make the
water more
fertile (productive).
As stated before, fertilization is sometimes
necessary to help a pond provide the nutrients directly
needed for
fish and plankton growth.
As a major food source of fish, plankton
must be kept healthy and in good supply.
Fertilizer supplements the elements the pond gets from its
own water
and soil. This is
especially necessary in ponds made in soil which
has used up the nutrients once available.
A WELL-FERTILIZED POND
A pond which has a lot of phytoplankton is often a bright
green color.
This color indicates a "bloom" of algae.
In a normal bloom, the Secchi
disc disappears at about 30cm depth; when the Secchi disc
disappears
at 20-40cm, the pond is very productive and fertile.
No fertilizer
is needed in a pond under these conditions.
Also, if the farmer places
his arm in the pond and his am disappears from sight at the
elbow,
the pond does not need fertilizer.
There is one more condition when no fertilizer is
needed. Sometimes
a pond can become too fertile.
If the Secchi disc disappears at only
15cm, the "bloom" is too thick.
The thick layer of green blocks the
sunlight from the pond and no oxygen can be made by the
phytoplankton.
<FIGURE>
12p94.gif (528x528)
In this case, there is too much
fertilizer, and the farmer must
take off some of the thick layer
of algae formed at the top of the
pond and stop using fertilizer
until the pond has recovered a
normal fertilizer level.
WHEN TO FERTILIZE
If the Secchi disc can still be seen at 43cm, for example,
or if the
farmer can still see his entire arm from fingers to shoulder
under the
water, there is not enough plankton.
And it is necessary to add fertilizer
to the water in order to prepare the pond for the fish.
One other factor which determines the need for fertilizer is
the quality
of the soil. If the
soil is very productive, the need for fertilizer
is small; if the soil is not productive, the need is
greater. A farmer
should know that the fertilizer he uses on his fields, if he
uses one,
can also be used in his fish pond.
The fish pond soil is often very
like the soil of the fields around it.
TYPES OF FERTILIZERS
The kinds of fertilizers used in fish ponds vary greatly,
depending on
the amount of money which can be spent and what is
available. Many
fish pond owners use organic fertilizers, or fertilizers
that come
from living things; such as cow dung--because it is
available on their
farms. Some big pond
owners like inorganic fertilizers, or chemicals
made by man, like the superphosphates.
But these chemical fertilizers
are expensive and sometimes hard to get.
Choosing fertilizer can be difficult.
The following paragraphs provide
more detail about organic and inorganic fertilizers and some
guidelines
to the proper use of each.
Organic Fertilizers.
Organic fertilizers can be plant or animal
products, such as:
Vegetable matter.
Chopped up manioc, sweet potatoes, or banana leaves,
kang kong, guinea or napier grass, or other such things that
have been
allowed to rot for a while.
The amounts of vegetable matter used as
fertilizer can be as high as 5,000 kg/ha.
Liquid manure.
Mostly animal urine containing uric acid, a source of
nitrogen. It is
washed out of buildings where animals are kept into the
ponds and used in very small amounts by mixing it with other
organic
fertilizers, such as cow or pig manure.
Household scraps.
Including garbage, grass cuttings, rice husks, and
human sewage, also called "night soil".
Animal manure.
Almost any kind of animal manure can be used as
fertilizer, including cow, pig, duck, or chicken dung.
Some manures
are better fertilizers than others.
The best way to use this kind of
fertilizer is to make a "soup" of it in a tank by
mixing it with water.
Use the liquid part of the "soup" in the
pond. Animal manure can also
be placed in a burlap bag hung from a stake in the
water. This way,
the nutrients from the manure will be released slowly into
the water
without the manure itself clogging up the pond bottom.
If this cannot
be done, then pile the manure in the corners of the
pond. Do not use
too much manure:
decaying manure uses up the oxygen in the pond --
particularly in hot, humid climates.
<FIGURE>
12p95.gif (437x437)
The best way to use these sources of fertilizer is to mix
them all
together in what is know as a compost pile.
A compost pile is simply
a pile of these organic materials which has been left to
rot. As
the materials decay together, they produce a substance which
is a
very good fertilizer.
Compost piles are important:
they provide the
very best kind of organic fertilizer for fish ponds and, in
many cases,
they cost nothing.
Making a Compost Pile
<FIGURE>
12p96a.gif (540x540)
For many years, compost has been made this way:
*
Pile organic matter, such as leaves, straw,
grass, rice husks
or other plant material
and household scraps about 30cm high.
*
Put a layer of animal manure (chicken, cow,
Pig, duck or whatever
is available)
on top of the first layer.
*
Sprinkle ashes and lime on the manure.
*
Repeat these layers of plant material,
manure, ashes and lime
until the pile
is about 1.5m high and 1.5 m wide.
*
Keep the pile moist, but do not let it get
wet.
*
Turn the pile every three weeks with a
shovel for about 3 months.
*
Use the pile in 3 months.
It will have decayed and shrunk to
about 1/10 of
its original size.
<FIGURE>
12p96b.gif (393x393)
There is now a faster way to make the compost ready to use
as fertilizer.
*
Make the same 1.5m x 1.5m pile of plant
material, manure, and
lime.
This time, however, use more household
garbage and animal
manure.
(Animal manure supplies nitrogen, an element
used by
plants during
the decay process. A good compost
mixture is about
1 shovelful of
manure to 30 shovelsful of the other organic
materials.)
*
Mix the material well.
Then cut all of it into small pieces, using
a shovel,
machete, scythe, etc. The pieces should
be about 3 to
5cm long.
Cutting the material speeds the rotting
process. (If
animal manure
is hard to get, add some inorganic fertilizer containing
nitrogen to the
compost pile.)
*
Turn the pile every few days.
Use a shovel to keep it well-mixed.
Compost piles
can get too hot in the middle if they are not turned
and mixed.
Put a stick into the middle of the
pile. Leave the
stick in the
pile for 3 minutes, and then pull it out.
If the stick
is hot, dry, or
smelly, the pile must be turned so that the inside
of the pile is
now on the outside.
*
Keep the pile moist, but not wet.
Protect it from the rain.
Animal
urine can be
used to keep the pile moist and helps add nitrogen to
the pile (pig
urine is best). A compost pile made in
this way will
be ready for
use in only 3 weeks.
When ready, pile the compost in the corners of the pond and
restrain it
with a screen; or cover the compost with a layer of mud to
hold the
plant material in place so it does not float into the
pond. The compost
releases its nutrients into the pond water gradually.
APPLICATION RATES
Fertilizer should be applied at a rate determined by the
area of your
pond. Area is the
length of the pond multiplied by the width.
For
example, if the pond is 10m wide by 20m long, it has an area
of 200
square meters ([m.sup.2]).
This is equivalent to 2/100 of a hectare.
The
measurements used for pond area are:
<FIGURE>
12p97.gif (353x353)
1 are
= [100m.sup.2]
1 acre
= 40 ares = [4000m.sup.2]
1
hectare = 100 ares = 2.5 acres = [10,000m.sup.2]
To fertilize a [200m.sup.2] fish pond with chicken manure,
at a rate of 200
kg/ha, you must only use 4 kg as follows:
[200m.sup.2] =
x
: 200 (200)
=
X ; X
= 4 kg
________
_________
_________
[10,000m.sup.2]
200 kg/ha
10,000
Most ponds are not as big as one hectare, so the farmer will
have to
determine his pond's area before using the manure.
It will be hard for
most farmers to calculate application rates in this way, but
it is
probably easy for you to develop some standard measures a
farmer can
use which are based on the average-sized pond in your area.
Often fish ponds are managed in conjunction with other
animals. Stables
are built right over the edge of the ponds, and the manure
and urine
from a certain number of animals are allowed to fall
directly into the
pond. This efficient
system works well for fish which can use animal
manure directly as food.
Pigs are often used like this because pig dung
makes a good food for some fish.
Fish ponds which share the area with
a number of ducks also show high yields of both ducks and
fish.
<FIGURE>
12p98.gif (486x486)
For the first fertilizer added to a new pond, some common
rates of
application of animal manures are:
Cow
dung 1000 kg/ha
Pig
dung 568 - 1704 kg/ha
Chicken dung 114 - 228 kg/ha
REMEMBER: Except for
compost fertilizer, only one kind of fertilizer
is needed at one time in a pond.
Only use one of the application rates
each time the pond is fertilized, or a combination of
fertilizers with
different rates to make up one rate.
That is, you can use 1000 kg/ha
of cow dung, or 500 kg/ha cow and 171 kg/ha chicken dung, or
about 300
kg/ha cow, 57 kg/ha chicken, and 284 kg/ha of pig dung.
After you fertilize
keep an eye on the pond.
Try not to over fertilize -- too much is
just as bad as not enough.
After the first application of fertilizer, application rates
do not
have to be as high.
Many older ponds do not need as much fertilizer
because the natural life of a pond tends towards becoming
more fertile
the older it gets.
However, each time the fish are harvested they
take part of the pond's productivity with them.
That is why older
ponds are still fertilized -- even though they may need less
fertilizer
than new ponds.
Inorganic Fertilizers.
Inorganic fertilizers are chemical fertilizers
that dissolve in the pond water and provide their nutrients
immediately.
Originally, inorganic fertilizers supplied nitrogen,
phosphorus,
and potassium, and they were called the NPK
fertilizers. Some typical
NPK fertilizers were8-8-2 (NPK) and 20-20-5 (NPK).
This simply
referred to the mix of fertilizer that each bag supplied;
for example,
8 measures of nitrogen, 8 measures of phosphorus and 2
measures of
potassium. Recent
studies show that if enough phosphorus is available,
the plants in the pond produce their own nitrogen, and that
potassium
is present already in small amounts in fish.
Presently, the only
element needed by fish that may be lacking in the fish pond
is the
element phosphorus.
Now, the most common inorganic fertilizers used in fish
ponds are the
phosphorus fertilizers -- basic slag, powdered single
superphosphate,
granular double superphosphate and triple
superphosphate. Some of
these fertilizers can last as long as three years in the
pond, so even
though they are expensive initially, they are often used in
fish ponds.
Research shows that the best fish growth occurs when
phosphate fertilizers
and organic fertilizers are used together.
Application rates of phosphate fertilizers are:
Basic
slag 25-30 kg/ha
Single superphosphate
114 kg/ha
Granular double superphosphate
57 kg/ha
<FIGURE>
12p100.gif (353x353)
Fertilizers have one purpose--to provide better growth of
fish in ponds.
Many organic and inorganic fertilizers are good.
Watch the pond carefully
for signs concerning a need for fertilizer.
As long as the water
is a green color, the pond is in good condition.
Remember:
it is
always best to do two things at once--wherever possible use
fertilizers
which can be used as food by the fish.
Now that the pond has been filled, the quality of the water
tested, and
the fertilizer added, the last step in preparing for the
fish is to
make sure that the food supply in the pond is sufficient for
the fish
that will be put into the pond.
Foods
It is important to be sure that fish have good food.
Feeding and
fertilization work together to make the pond successful.
The growth of fish in ponds is directly related to the
amount of food
available in the pond.
The pond must provide all the food and nutrients
fish need. But all
fish do not need the same kinds of food:
different
species eat different types of food, and fish eat different
foods depending
on the stage of their life cycle.
Newly-hatched fry eat from their yolk sacs until the sacs
are gone.
The fry then eat the smallest phytoplankton in the
pond. As the fry
get bigger, they can eat bigger foods.
Adult fish eat the things that
their particular kind of fish enjoy--plankton, higher
plants, worms,
insect larvae, etc.
TYPES OF FISH FOOD
Fish foods can be natural (those found naturally in the
pond) or supplementary
(those foods added to the pond).
Natural Foods. These
foods are the phytoplankton, zooplankton, detritus,
snails, worms, insects and insect larvae, small plants like
duckweeds
and various other weeds and grasses that can be found in a
fish pond.
(See illustrations of Natural Foods at the end of this section.)
Also,
if the fish is carnivorous and eats the flesh of other
animals, small
fish are a food source.
Some fish eat all these foods; some prefer only one kind of
food.
Often a fish will choose one kind of food over another, even
though
either of the foods would be eaten by the fish if the other
food were
not available.
Natural foods are the best foods for fish.
The farmer
should encourage, as much as possible, the growth of these
natural
foods--through maintaining the quality of his water, proper
fertilization
of the pond bottom and the water, etc.
Sometimes, however, the farmer must add food to the pond
because the
pond is not producing enough food for good growth.
The best supplementary
foods a farmer can put into the pond are extra natural
foods.
But there are a great number of other foods which fish will
eat.
Supplementary Foods.
Almost anything can be used as a supplementary
food, depending on the fish species in the pond.
Typical supplementary
foods are: bread
crumbs, rice bran, fish meal, ground-up maize,
broken rice, soy bean cakes, peanut cakes, corn meal,
cottonseed oil
cakes, oats, barley, rye, potatoes, coconut cakes, sweet
potatoes,
guinea grass, napier grass, kang kong, manioc, water
hyacinth, wheat,
silkworm pupae, and left-over animal feeds and some animal
manures.
As stated previously, the kind of extra food depends on the
kind of
fish. Tilapia, for
example, will eat almost anything, including the
supplementary foods listed above.
This is one reason why they, are
such very good pond fish.
The silver carp, on the other hand, will
eat only phytoplankton, even when it is a fish of marketable
size.
The farmer must know what his fish will accept before he
puts the
fish into the pond.
NOTE TO DEVELOPMENT WORKERS
Some of these supplemental foods are better at encouraging
growth than
others. The value of
each food is measured in terms of how quickly
and well it can help the fish gain weight.
The amount of a food that
can be converted into fish flesh by the fish is called the
conversion
ratio. And because
these foods are given to help the fish grow, each
food has what is known in various places as a growth
co-efficient,
food quotient, or its nutritive ratio.
The food quotient is figured by dividing the total weight of
the food
by the total increase in weight gained by the fish over a
period of
time. This is done
as follows:
Food
Quotient = weight of food given
__________________________
increase in weight of fish
For example, a fish weighing 100g is fed a supplementary
food at a
rate of 5% of his body weight, or 5g per day.
The fish weighs 160g
at the end of a 30-day period.
Therefore, the food quotient of this
particular food is:
Food Quotient
= 5g (30 days) =
150
____________ ___
(160-100g) 60
Food
Quotient = 2.5
In other words, the fish has been able to use about 2.5g of
food to
gain 1.0g of weight a day.
This is a good conversion ratio.
The table shown here lists food quotients of some kinds of
supplementary
foods used with common carp.
The lower the value of the quotient,
the better the food was used by the fish.
For example, dried silkworm
pupae help the fish grow faster than do fresh silkworm
pupae. REMEMBER:
the conversion of foods depends upon the ability of the
individual
fish to use the food given to it.
And that ability differs according
to species.
FOOD
QUOTIENTS OF COMMON CARP FEEDS
FOOD
FOOD
QUOTIENT
Fresh silkworm
pupae 5.0 - 5.5
Dried silkworm
pupae 1.3 - 2.1
Chironomids
2.3 - 4.4
Fish meal
1.5 - 3.0
Rice bran
5.1
Soy bean
cake
2.2
Clam meat
1.3
Cottonseed cake
3.0
Dehydrated
blood 1.5 -
1.7
Maize
4.0 -
6.0
____________________________________________________________________
Source:
Bardach, et. al., Aquaculture
It will be hard or impossible for many farmers in your area
to figure
these ratios and quotients.
For the farmer who is new to the effort
and has few resources, it may be a good idea to direct him
to the
supplementary foods having the best conversion ratios for
his fish.
<FIGURE>
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12p105.gif (600x600)
12p106.gif (600x600)
<FIGURE>
<FIGURE>
6 Managing
the Pond
It should be clear by now that much of the success of a fish
pond depends
upon careful planning.
Before the farmer could build the pond, it was
necessary for him to think through why he wanted the pond --
for food,
profit, or both, what kind of ponds he could build on his
land and what
kind or kinds of fish are best suited to his climate and
pond conditions.
Only when all these factors were thought out could the pond
be built.
Now, with the pond constructed, fertilized, and otherwise
prepared for
the fish, the farmer is ready to put the fish into (stock)
the ponds
and get to the business of raising fish.
Stocking
Stocking is the word used to describe the act of placing the
fish (stock)
into the pond. The
stocking density is used here to refer to the total
number of fish which can be put into (stocked) in a pond.
<FIGURE>
12p107.gif (486x486)
The stocking rate is the term used to refer to the number of
one species
which are put into a pond.
Therefore, in a monoculture pond, the
stocking rate is the same as the stocking density because
there is only
one kind of fish.
In a polyculture of Chinese carp, however, the stocking
density, or the
total number of fingerlings, may be 20,000 per hectare.
Of this total,
the stocking rate looks like this:
grass carp are stocked at a rate
of 5,000; 5,000 are bighead carp; 10,000 are silver carp.
<FIGURE>
12p108.gif (486x486)
Stocking rate and density are important.
There is only enough food and
room in a pond for a certain number of fish.
The good growth of fish
depends upon putting the right number of fish into the pond.
The age of the fish must also be considered when stocking
ponds. For
example, more fingerlings can be placed in a pond than brood
fish, because
fingerlings require less food per fish than brood fish.
If the food
available in the pond is not supplemented, proper stocking
rates and densities
are even more important.
STOCKING DENSITIES
The farmer must know how many fish he can put into his pond
so that he
can get the right number--either from the market or from a
local stream
or lake. He should
remember, when he decides upon this number, that
some of the fish will die--both when they are put into the
pond and
later. The following
paragraphs provide some guidelines to use when
stocking a pond with some of the more common pond fish.
Common Carp.
Stocking densities differ with the age and size of the
fish. In general,
the more volume of water a carp has, the better is
its growth. This
assumes that the pond contains enough food, and the
water temperature is right.
The best growth of common carp has been
shown with stocking densities of about 10,000 to 20,000 fish
per
hectare; more with fry; less with post-fingerlings.
Some ponds use
running water, and in these ponds, they have been able to
stock up to
850,000 fry per hectare with only a 20% mortality rate.
Tilapia. Tilapia
have been stocked in amounts ranging from 1000 fish
per hectare to about 50,000 fish per hectare when supplementary
food
was provided. But
stocking densities really depend on the rates of
reproduction of tilapia, and whether they can be separated
by sex or not.
Chinese Carp. In
general, the stocking rates can only be found by trial
and error, and often will be different from time to time,
depending upon
the availability of fry.
In Malaysia, a ratio of carp stocking has been
suggested of 2:1:1:3 for grass carp, bighead, silver carp
and common carp.
This means that if there were a stocking density of 7 Chinese
carp, 2
fish would be grass carp, 3 would be common carp, and there
would be only
one each of bighead and silver carp.
This is a good stocking rate for
this density. The
density for a given pond has to be figured in terms
of what the pond can support.
Indian Carp.
Stocking densities of Indian carp are not widely known.
Some densities range from 4,000 to 11,000 fry or fingerlings
per hectare,
but again, the density depends upon the amount of food
available to
the fish.
When stocking ponds to produce market-size fish, remember
that the more
fish stocked, the more food must be available for the best
possible
growth in ponds.
The following paragraphs describe the proper methods for
carrying new
stock from the market or river to the pond, and for placing
them into
the pond.
STOCKING FISH IN PONDS
There are some general rules which apply when bringing fish
from one
place to another:
*
do not handle the fish too much
*
make sure the fish get enough oxygen
*
keep the fish from getting too warm or too
cold
*
stock or transfer fish in the early morning
when temperatures
are lower and
the fish are less active.
If fish are stocked so that there is enough oxygen, no
temperature
difference between the stocking water and the pond water,
and they are
not touched, the fish will not be stressed and will survive
the stocking.
Here are more details concerning the stocking of fish at
different
stages in the life cycle.
When fry are being moved for a short distance only, for
example, from
a nursery pond to a rearing pond, they usually are carried
in small plastic
or metal tubs, or in baskets.
<FIGURE>
12p110a.gif (486x486)
To move fry successfully:
*
Scoop the fry out of the river or pond in
jars, cups, or
small nets.
<FIGURE>
12p110b.gif (393x393)
*
Put the fry into a bucket of water.
*
Carry the bucket to the pond where
the fry will
be placed.
*
Check the temperature of the water
in the bucket;
it should be the
same
temperature as the water in
the pond where
the fry will be
stocked.
<FIGURE>
12p111a.gif (285x285)
*
Add water from the pond to the bucket slowly
-- until the
temperature of
the water in the bucket is the same as the
temperature of
the water in the pond.
*
Tip the bucket slowly into the pond, and let
the fry swim
out into the
pond themselves.
REMEMBER: SOME FRY
WILL DIE EVEN WHEN HANDLED VERY CAREFULLY.
THIS IS
TO BE
EXPECTED.
Moving Fry for Longer Distances.
If the fry are to be taken from a
market or river which requires a few hours travel or a long
distance,
they must be protected better.
One method, which can also be used
for fingerlings (and some small adult fish), is to:
*
Place fry into plastic bags filled 1/3 with
water.
*
Fill the rest of the bag with oxygen.
The oxygen is
put into the
bag with a hose placed directly into the
water so that
the oxygen bubbles into the water.
<FIGURE>
12p111b.gif (317x317)
*
Tie the bag tightly so that the
oxygen does
not leak out.
<FIGURE>
12p112a.gif (317x317)
*
Place the plastic bags into tin boxes or
cardboard boxes
or in woven
grass bags. These containers give added
protection.
<FIGURE>
12p112b.gif (353x353)
*
Change the water in the bags after 6
hours. The oxygen will
last only that
long.
*
Make sure the bags do not get too hot and
that the temperature
of the water
in the bags stays at about the same
temperature as
the water from which the fingerlings or
fry were
taken.
*
Place the bags in the pond unopened until the
water temperature
inside the
bags is about the same as the temperature in the pond.
<FIGURE>
12p113a.gif (353x353)
*
Open the bags and let some pond water in.
*
Let the bag fill up slowly, and the fish
will swim out into the
pond by
themselves.
This process may take a little while, but it is far better
to take the
time than it is to lose the fry.
NEVER POUR FRY INTO A POND.
This will
shock them and kill them all.
Stocking Fingerlings.
Fingerlings are stocked in the same way as fry.
Always remember that the water in their container must be at
the same
temperature as the water in the pond.
Then let the fingerlings swim out
of the container into the pond by themselves.
DO NOT POUR FINGERLINGS
INTO THE POND. They
may die because of the shock of hitting the water
or the sudden change of temperature.
Some fingerlings will die during
stocking. But
usually these are the weaker fish.
Careful handling will
mean less loss of fingerlings, as well as fry.
<FIGURE>
12p113b.gif (486x486)
Stocking Adult Fish.
Adult fish are a little more difficult to stock
than fry or fingerlings.
First, they are large (from 0.5kg up to
3.0kg) and can injure people and themselves by jumping out
of containers
or ponds when they are being carried or caught.
For example, Chinese
carp often hurt themselves this way.
This problem is controlled by
placing a net of some kind on top of the container so they
cannot jump
out.
To move fish from one pond to
another, or from a pond to a container,
make a carrying cradle.
Use fishnet and pieces of wood or
bamboo for handles.
The cradle is
placed around the brood fish in
the water. Then the
fish can be
lifted out of the water and carried
to the new pond or to the container
for transporting.
There the cradle
is released and the brood fish
swims away. Brood
fish must never
be thrown into a pond.
<FIGURE>
12p114a.gif (353x353)
Adult fish often are nervous when being taken from one place
to another.
Some pond owners even put a hand or a handkerchief over the
fishes' eyes
when they are carried.
Care is necessary when handling, however:
brood fish particularly are sensitive
to being handled.
They bruise easily
if they are held tightly, and the
bruises can become sites for infection.
<FIGURE>
12p114b.gif (353x353)
Brood fish are often carried in tubs
or drums half-filled with clean, well-
oxygenated water when they must be
carried a long distance.
Change the
water often and check the water temperature
each time. If the
brood fish
are very active, mix a solution of 1
to 4 grams per liters of urethane in
the water. This will
make the fish
slow and less active, so they can
be moved without injury.
Routine Pond Management
After the ponds are stocked, ongoing management of the pond
includes:
*
feeding and fertilizing as necessary
*
keeping the pond in good condition
*
watching for trouble and disease
Each pond, whether it is small or large, one pond or one of
several,
requires supervision in the above areas.
And good management requires
that checks of the condition of the fish and the pond be a
regular
part of the pond owner's day.
Guidelines for both daily and monthly
general maintenance are given here.
Then, since fish in ponds are
treated somewhat differently depending upon their species,
and their
stage in the life cycle, more detail on managing fry and
fingerlings
and managing brood stock is given.
DAILY MANAGEMENT
Ponds and the fish in them must be taken care of every
day. It is a
good idea to have the pond owner follow a checklist of
things to do.
Daily care will greatly lessen the chance that something
will go
wrong in the pond.
A good checklist might look like this:
*
check the pond for leaks
*
clean filters
*
watch fish behavior near the feeding area
*
feed the fish
*
add fertilizer, if necessary
*
watch for predators
IMPORTANT: Check the
ponds at the same time each day. Early
morning
is the best time because oxygen levels in the water are
lowest then,
and the fish are more likely to have trouble at that time of
day--if
they are going to have trouble at all.
Each step on the checklist involves certain activities and
is discussed
in more detail here.
Checking for Leaks.
Check all walls, gates, inlets, and outlets.
It
is possible for a plug on a drainage pipe, for example, to
work loose,
or partly loose, so that water leaks from the pond.
Walls made of
hard-packed earth can erode (wash away), especially after
heavy rains.
Little leaks get larger quickly.
It is important to be sure the
farmer realizes that in a pond only 2m deep, for example,
loss of
even part of the water can create problems for the fish.
Cleaning Filters.
Again, this is very important.
Any filters in the
pond must be removed and cleaned of silt, leaves, or other
materials
that have collected in them.
A dirty filter at the outlet pipe
could slow down the drainage process.
Watch the Fish. A
farmer can tell much about his fish by watching
them carefully. If
they are swimming quickly and easily around the
pond, they are well.
If they are waiting near the surface, they are
likely to be hungry.
If they are gasping for breath at the surface
of the water, there is not enough oxygen and the farmer will
know he
has to act quickly to aerate the water in the pond.
Feed the Fish.
Remember: in some ponds it is
not necessary to feed the
fish extra food. The
pond can be made rich enough to fill all the
food needs of the fish.
However, some ponds and some fish require supplemental
feeding. And,
sometimes, even a pond which has provided
enough food before has to have food added to it.
Supplementary foods are given by:
*
spreading the food over the water's surface,
as with
bread crumbs
and rice bran
<FIGURE>
12p116.gif (486x486)
*
placing food inside a floating bamboo or
rope feeding
ring (which is
attached to the bottom of the pond)
*
pressing food into dry pellets which float
in the feeding
ring or fall
to the bottom under the ring
<FIGURE>
12p117.gif (393x393)
Guidelines for Feeding Fish
Here are some good guidelines for feeding fish which might
prove useful
to the farmer:
*
Always feed the fish at the same time and in
the same part
of the
pond. The fish will learn where to go
to get food.
Then, when the
fish come near the surface of the water, inside
the feeding
ring, for example, the farmer can see how
well they are
eating and growing.
*
Do not overfeed.
Give only the amount of food the fish
will take at
one feeding. Too much food will not get
eaten, but
will decay and, therefore, will use up valuable
oxygen from
the pond during the decaying process.
The amount of
food can be found by experience. And of
course, the
younger the fish, the less food they will need.
A farmer is
wise to start with a smaller amount of a food.
Then, if the
fish seem to be waiting near the surface in
the feeding
area, he will know more food is required.
There are more
exact ways to determine how much food to feed
the fish.
Most pond owners feed fish at the rate of 2
to
5% of body
weight per day. Therefore, 100
fingerlings
weighing 6g
each (a total weight of 600g) would receive
5% of 600g, or
30g of food a day. One hundred fish of
breeder size
weighing 1kg each, (total weight 100kg) would
require 5kg of
food a day.
Making such
measures and calculations is not possible
for many
farmers. Therefore, it is best that
they know
which foods to
give, how to give them, and how to judge when
the fish are
or are not getting enough food.
*
Feed fish only 6 days each week.
This will give the fish
a chance to
feed on whatever food remains in the pond.
Too much food
can clog the gills of fish, particularly
those fish who
eat only very fine particles of food.
*
Do not feed fish for at least one day before
harvesting
or breeding
them. When the fish eat, they void
(empty)
the waste from
their bodies into the water. This
happens
even more when
the fish are stressed. The combination
of food and
wastes makes the water turbid and
increases the
stress that is already placed on fish by
the breeding
and harvesting processes.
*
Feed the right kinds of foods.
Some fish will eat almost
any of the
foods mentioned in the section on "Preparing the
Pond." Other fish are not
as easy to please. The farmer
will have to
experiment with supplemental foods. If
he
gives food one
day and it is not eaten, he should stop
that food and
try another. Again, if he starts with
small amounts
only, he is not likely to run into trouble.
While it is a
good idea to test those foods most available
to a farmer,
here are some guidelines to feeding a
number of pond
fish.
Common Carp
Common carp feed well on the natural food produced in the
pond. However,
pond owners often give common carp supplementary food, so
the fish will
gain weight quickly.
Some good supplementary foods for common carp
are dried silkworm pupae, fish meal and clam meat.
However, these carp
will eat almost anything.
Suplementary foods such as these are not
necessary. The best
way to increase common carp growth rates is to
fertilize the pond well so that the pond produces a good
supply of
natural food for the carp to eat.
Tilapia
Not much is known about the feeding habits of some of the
tilapia,
for example, Tilapia nilotica.
Tilapia mossambica and Tilapia zillii
are used to control filamentous algae, which is a habitat
for mosquito
larvae, thus the tilapia is used to help with malaria
control.
Tilapia are hardy and accept many foods.
Most tilapia ponds can be
managed in much the same way as carp ponds.
Chinese Carp
Chinese carp fry eat plankton, so it is important that they
be placed
in a well-fertilized pond with a good supply of natural
food. Fry
can be fed supplementary foods after a while.
These foods include
egg yolk which is strained through a cloth into the pond,
soybean meal,
rice bran, and peanut cake.
Once the fingerlings get larger, they can
be fed like common carp.
Remember, however, that the small pond owner is likely to
have Chinese
carp as part of a polyculture.
If the polyculture has been planned
wisely, the Chinese carp will not need to be fed extra food.
Indian Carp
Young fry of Indian carp, like all carps, feed on the
plankton in the
pond. Normally fish
ponds in India are fertilized by draining the
pond and drying, then adding a fertilizer made of some
animal manure
mixed with oil cake at the rate of 200 to 325 kg/ha.
This produces a
good bloom of plankton for the newly hatched fry.
However, it has
now been shown that the Indian carp prefer zooplankton,
though sometimes
they are given supplementary foods.
After the fish reach fingerling
size, no supplementary food is given.
Note that in any pond, the fish can be kept healthy,
well-fed and
growing well by making sure the pond is well-fertilized so
that it
produces its own food.
As a general rule, it is better for most small
farmers to work at keeping their ponds well fertilized or to
find
natural foods which can be added to the pond.
Most small farmers do not
have extra foods to share with fish, but they do have access
to organic
fertilizer materials, such as manure.
Fertilize the Pond.
The section on "Preparing the Pond" discussed
kinds of fertilizer, so the farmer should already be
familiar with
what fertilizers can be used in ponds.
Again, the right fertilizer
is a matter for experiment and experience.
The farmer has already used fertilizer before filling the
pond. Now
he must watch the water carefully each day.
If the healthy green
color of a fertile pond is not there or if the water has
become
brown, fertilizer is needed.
Fertilizers are applied depending upon
what kind they are:
REMEMBER: organic fertilizers do
not provide
their nutrients right away; inorganic fertilizers work very
quickly.
A farmer who uses mainly organic fertilizers would probably
be wise
to keep some amount of inorganic fertilizer on hand for
those times
when he needs the fertilizer to work quickly.
Fertilizers are added to the pond in a number of ways:
*
Leaves, grass, and animal manure may be left
in piles
around the
inside edges of the pond. This is
probably
not a good way
to fertilize in a hot, humid climate
where the
faster decay process would result in faster
use of oxygen.
*
Liquid manures and "soups" are
dipped into the pond
around the
edges or in the deepest water.
*
Powdered fertilizers (chicken manure, superphosphates)
are broadcast
(sprinkled) in a fine layer over the
entire surface
of the pond.
<FIGURE>
12p120.gif (393x393)
*
Some fertilizers are left on platforms in
the pond.
The platforms
are submerged near the surface of the
water and confined
behind a screen.
<FIGURE>
12p121.gif (437x437)
Watch for Predators.
Check the pond area for signs of snake holes,
rat burrows, eels, and strange fish which may have entered
through
holes in an inlet screen for example.
Any of these can be very
dangerous in a fish pond, particularly to a pond containing
fry or
small fingerlings.
Make sure fences which protect ponds from farm
animals who might eat grass off the walls or break down the
walls of
the pond have no breaks in them.
Not each of these things will require much time each
day. But a good
pond manager will at least check each of these items daily.
MONTHLY MANAGEMENT
Ponds which are managed well day by day will require little
other
treatment. However,
the following things will probably require more
careful attention every month or so:
*
Check the pond walls.
Cut grass which is too long or
plant more, if
necessary.
*
Check the pond bottom.
If there is too much buildup of
silt and
organic matter, shovel or scoop this material
out.
<FIGURE>
12p122a.gif (486x486)
*
Check for and remove weeds or other growth
which might be
a problem at
harvest time or when a net is used in the pond.
*
Give the walls and inlet and outlet systems
an especially
careful check
for leaks and for blockage. Make sure
the
water can flow
smoothly in and out of the pond, so that
if water needs
to be put in or taken out quickly, there
will be no
problem.
*
Check the fertility and turbidity of the
water. Even a
pond
well-fertilized at the beginning may need more fertilizer
after a month
of operation.
*
Check the fish carefully for signs of
disease. If all has
gone well
during the month--the fish have gained weight
and their
gills are a healthy red color--the chances are
that all is
well. But the fish should be checked
especially
carefully for
signs of disease each month. (See
"Problems
of Fish
Cultured in Ponds.") It does not
take long for a
disease to
infect an entire pond full of fish.
<FIGURE>
12p122b.gif (393x393)
*
Add lime if needed.
If the farmer has been adding
fertilizer and
feeding his fish regularly, but the
fish still do
not seem to be gaining weight well or
moving in the
water well, the water quality may
need
adjusting.
Good management is a key to a good fish harvest.
It is important for
the farmer to realize this and to work fish management into
his
daily schedule. But
this is not always easy for him to do.
In many
parts of the world, farmers let their animals manage
themselves, i.e.,
find their own food, etc.
This will not usually work with a fish
pond. Fish cannot be
put into ponds, left alone, and expected to
grow and provide food and income.
Successful fish pond operation requires
active attention by the farmer.
The management guidelines just described apply to all fish
ponds,
regardless of type of fish or stage of growth.
There are, however,
some differences between managing a fry or fingerling pond
and managing
brood stock. So
these differences should be looked at more closely
here.
Management of Fry and Fingerlings
There are several ways to get fry.
If the farmer is breeding fish,
then he will have his own source of fry to bring to the
rearing ponds
from the smaller nursery (hatching) ponds.
If the farmer has a small
backyard pond, where he raises fish from fry or fingerlings
to market
size, he either gets his young fish from a market or another
farmer
or scoops them out of natural waters.
<FIGURE>
12p123.gif (393x393)
Wherever the young fish come from,
it is important for a pond owner to
know how many fry or fingerlings he
is putting into his pond.
If the
owner knows how many fish are going
into the pond he will know at harvest
time how many fish died (the
mortality rate) before they were
ready for harvest.
This information
can help the farmer make decisions about his management of
the pond.
If, for example, more than half of the fish in a pond died
between
the time they were put in as fry and the time of harvesting
for
market, too many fish are dying; the farmer ought to find
the reasons
why before he begins again.
<FIGURE>
12p124.gif (393x393)
COUNTING FRY
Fry are very delicate and must be handled gently.
Here is one way of
counting them:
*
Take a basin or tub of which you know the size
(50-100 liters)
*
Put all the fry into this basin.
*
Scoop up fry into a 200-250ml measuring cup.
*
Count the fry in the measuring cup by slowly
and gently
pouring the
fish back into the basin.
*
Estimate the total number of fry in the
basin by setting up
a ratio like
this.
number of
fry in measuring cup =
volume of measuring cup
number of
fry in basin (total) =
volume of basin
For example, a
measuring cup of 250 ml holds 100 fry.
Therefore,
it is
estimated, using this formula, that a 50 l basin full of
fry holds
20,000 fry.
Here is another way of counting fry which is somewhat easier
because
it does not depend upon cups and basins of any particular
size.
*
Put all the fry into an old container--an
old metal garbage
can, an oil
drum, a washtub.
*
Get an old milk can, or some other smaller
container, and
make sure one
end is cut off.
*
Fill the smaller container with strained
water.
*
Mark a line on the garbage can to show the
level of water
being put in.
*
Fill the milk can and pour the water into
the larger can.
*
Continue to fill the smaller can and dump
water from it into
the larger
can.
*
Count how many small cans of water it took
to fill the larger
can as high as
the line drawn on the can.
*
Fill the smaller can with fry and count them
carefully.
*
Estimate the number of fry by multiplying
the number of fry
in the milk
can by the number of cans it takes to fill the
large
container to the line marked on it.
Therefore, if
there were 50 fry in one milk can, and it takes
25 cans to
fill the larger container to the mark, there are
50 x 25 or
1,250 fry.
Fingerlings are easier to count than fry because they are
older and
larger. The same
kind of measuring system could be set up.
But the
containers would have to be able to deal with the larger
fish. A
farmer who has raised his fingerlings from fry should count
the fingerlings
as he sells them or moves them from a nursery pond to a
rearing
pond. Then he will
know how many survived. If a farmer
started
with 20,000 fry and had 15,000 fingerlings, 5,000 fry
died. But this
is a death rate of only 25%--which is not a terribly high
figure.
Again, the farmer must accept that some of his fish are
going to die.
A pond owner who raises fish is more likely to be able to
handle fry
successfully. Fry
are very delicate and must be protected carefully
from predators and sudden temperature and oxygen
changes. The fry
hatch from their eggs in 12 to 72 hours depending upon the
temperature
and the type of fish.
The fry then live off the yolk sac which is
attached to them.
This sac lasts several days. But
then the farmer
must be sure that the water provides enough food for the
fry.
Many pond owners feed the fry with the yolk of a hard-boiled
chicken
egg that has been strained through a cloth with water.
After a few
days of this, the fry can begin to eat the phytoplankton and
the
zooplankton in the pond.
Make sure that there is always enough food
for the fry to eat before you transfer the fry to the
rearing pond.
For a farmer who has only one new pond, it is probably a
better idea
for him to start with young fingerlings.
This will give more chance
of success than starting with fry.
This is not to say that a farmer who has only one pond
cannot start
his fish crop from eggs or fry.
He can. One way this can
be done is
to keep the eggs in a washtub or large container rather than
a pond.
The eggs must have plenty of oxygen, so the water must be
changed often.
Any unfertilized eggs must be removed so that they do not
cause infections
in the fertilized eggs.
Unfertilized eggs are white; fertilized
eggs are yellowish red.
Keeping fry in a smaller container is a good idea because it
allows
the farmer to better control the surroundings.
Fry often get
bacterial and fungal infections and are a favorite target of
birds.
Again, the water must be kept rich in oxygen and food which
can be
eaten by fry.
The care of eggs and fry is very difficult and very
important. A
farmer who wishes to breed fish must certainly work to gain
experience
handling delicate eggs and fry.
A farmer who wants only a food source
in his backyard may wish to take the easier road and start
with
fingerlings.
The size of fingerlings depends upon climate, water
temperature, food
given, and the number of fish stocked in the pond.
The following are
some average sizes and weights common in the Philippines:
Average
Average
Lengths
Weights
Milkfish
6.57cm
2.9 grams
Tilapia
6.33cm 5.8 grams
5.64cm
5.6 grams
Silver Carp
7.39cm
7.1 grams
Common Carp
7.39cm
7.1 grams
Fingerlings may be fed supplementary food if it is
necessary. Remember
that fish usually receive supplementary food which is about
5%
of their body weight per day.
This was discussed in more detail in
the section on preparing the pond, so there is no need to go
into
detail here.
It probably is a good idea, however, to note again that
farmers should
proceed slowly when giving supplementary foods.
Add only small amounts
of food and watch the fish carefully to see how they accept
it. And
the most important thing is to make sure the pond is
producing enough
of its own food.
<FIGURE>
12p127a.gif (486x486)
If the guidelines for management, discussed earlier in this
section,
are followed, the fingerlings should grow well.
When the fish reach
a good size (the size preferred in the farmer's area -- some
people
like smaller, rather than larger fish), they can be
harvested and
sold.
A well-cared-for fence protects
this farmer's pond from unwelcome
visitors.
<FIGURE>
12p127b.gif (437x437)
Breeding is the term used to describe the complete
reproductive cycle of
fish. Successful breeding
depends on the health of the brood stock and
the ability of the fish to spawn.
Spawning describes the actual release
of eggs and sperm by the adult fish, and the fertilization
of the eggs
by the sperm. This
section gives information concerning the breeding of
pond fish.
Management of Brood Stock
A brood fish is a fish that has reached its full growth and
is able to reproduce.
The age at which this happens depends upon the kind of fish,
the
climate, the quality and amount of food.
The specific characteristics of
brood fish are basically the same for every fish
species. In general,
good brood fish are:
*
well-formed and unbruised
*
free of parasites and disease
*
lively and active
*
a few years old, between 0.5kg and 3.0kg
(depending upon species)
*
sexually mature (so they can be separated by
sex)
<FIGURE>
12p128.gif (256x256)
Other characteristics used in choosing good brood stock are
relative size
and the large, rounded abdomen in the female fish.
Choosing brood stock of common carp is more difficult.
The characteristics
of these fish are:
*
moderately soft body
*
broad and flat lower side of belly, so that
the fish
can stand on
its belly
*
relatively great body depth compared to
length
*
broad, but supple, caudal peduncle
*
small head and pointed nose
*
rather large and regularly inserted scales
*
genital opening nearer to the caudal
peduncle than in the
average carp
In general, the larger the female carp, the more eggs it
will produce.
A carp of 45-50cm can produce up to 310,000 eggs; a carp of
60-65cm produces
up to 1,507,000 eggs at one time.
But older carp (5 years and up)
will have eggs that are not as healthy as those of younger
carp (2 years
old), so size is not the only factor in choosing good
breeders. Good
breeders usually are younger fish weighing 1 to 2 kg.
Brood fish can be obtained from natural waters by seining
(netting) or
traps, from fish dealers or fishermen, from other pond
owners, or from
government fish farms.
Select more males than females, so that when a
female is ready to spawn, at least one male also will be
ready.
The numbers of breeders needed depends upon the size of the
brood pond.
For example, a carp weighing 1 kg needs about [5m.sup.2] to
live and spawn.
Therefore, a brood pond of 0.5 ha (5,000 [m.sup.2]), will
hold 1,000 brood fish
of an average I kg weight.
Most brood ponds are much smaller than this,
however, so the farmer must calculate the number of fish to
place inside.
After some experience, the farmer will be able to judge the
correct
numbers for his pond quite easily.
After choosing the breeders, treat them for possible
parasites or
disease before placing them into the brood ponds.
This treatment is done
by placing the fish, one by one, into a bath of 10 ppm of
potassium
permanganate for 1 hour, them transferring them to a bath of
15 ppm of
formalin for another 4 to 12 hours.
These mixtures can be prepared in
washtubs. After the
fish are treated, they can be placed into the pond.
Of course, brood fish coming from a source which is known to
be uncontaminated
and free from disease would not require this treatment.
(Further information on treating fish for disease is found
in "Problems
of Fish in Ponds.")
The brood stock must be well cared for.
If they are in good health, the
eggs will be healthier.
It is probably more important to feed brood
stock with supplementary foods than it is to give
supplementary food
to fish at any other stage of growth.
Feed them rice bran, so bean
cakes, or other processed foods at a rate of 5% of body
weight per
day. They should be
managed carefully according to the general guidelines
discussed earlier.
Remember: brood stock should not
be fed for
at least one day before they are caught for breeding.
When caught by net, examine the brood stock carefully and
handle them as
little as possible.
Use a cradle to handle and carry the fish from one
pond to another.
They should be carried to a spawning pond, stocked in
the proper manner, and left to spawn.
After spawning has occurred, the
brood fish should be caught again and carefully carried back
and released
into their brood pond.
Always remember to treat brood stock well, and never select
a fish for
spawning which does not show the proper signs of readiness
to spawn.
(See the following information on spawning behavior.)
Spawning in fish ponds is done in two ways:
*
Natural spawning -- the fish are placed in
ponds and left
to spawn by themselves
*
Induced spawning (artificial propagation) --
methods used
by man to make (induce) the fish release
their eggs and sperm
Both of these spawning methods have advantages and
disadvantages.
Natural Spawning.
Fish who spawn naturally require only a well-prepared
brood pond. Use a
net to seine the pond and choose good breeders.
Then
introduce them into the spawning pond.
Most fish will spawn the first
night in the new pond; if they do not spawn, then leave them
alone for
a few more days. If
they still do not spawn, remove them and start
again with some other breeders.
Each fish used in pond culture has very definite and very
different needs
to spawn naturally in ponds.
To encourage spawning, ponds can be prepared
differently depending upon the fish.
Therefore, the best way to
prepare is to understand how that fish would spawn in
nature. The
following describes the natural spawning behavior -- in
nature and in
ponds -- of some of the more common pond fish.
THE COMMON CARP -- Spawning in Nature
In China, common carp spawn in the rainy season when the
water level and
temperature rise at the same time.
This rise in temperature and water
level is a signal to the carp to begin maturing sexually.
When they are
fully mature (ripe), they begin their mating behavior, which
includes
chasing each other in and out of the plants floating on the
water surface.
The farmer who sees his common carp doing this has a good
indicator that
his fish are ready to spawn.
When common carp are ready to spawn, the female carp begins
to swim in
and out of the plants.
She then releases her eggs on the plant roots.
The male follows her very closely.
As she releases her eggs, he releases
his sperm (milt); the sperm fertilizes the eggs.
Carp eggs are slightly
sticky (adhesive) and they stick onto the plant roots just
under the
water surface until they hatch.
Depending on the temperature of the
water, the eggs hatch in 2 to 6 days.
<FIGURE>
12p131a.gif (437x437)
The new common carp fry feed off of their yolk sacs for
another 2 to 6
days, until it is absorbed, and then begin to feed on the
zooplankton
in the pond water.
The carp can spawn all year round in nature, as long
as the water temperatures stay high, because a carp is capable
of
breeding once every two or three months.
<FIGURE>
12p131b.gif (437x437)
THE COMMON CARP -- Spawning in Ponds
The best way to spawn common carp in fish ponds is to try
and reproduce
the natural conditions of high water levels and
temperature. First the
fish are taken from a cool pond and put into a pond with
warmer water.
Then the water level in the pond is increased.
This provides the
signal for the carp to mature sexually.
When the fish mature, place
egg collectors, called kakabans, in the pond, or just some
water plants
with roots that hang down.
After the introduction of the kakabans, the female fish
begin to investigate
the fibers. Soon the
females will begin spawning behavior and the
fish will spawn on the fibers of the kakaban.
Because the eggs are
sticky, they stick to the kakaban, and the entire kakaban
can be lifted
and transferred from the breeding pond to the nursery pond.
Important: Common
carp are omnivorous; that is, they eat anything --
including their own fry.
It is best to transfer the full kakabans to
another pond for hatching.
A kakaban is a floating mat that uses a fiber like inkjuk,
or beaten palm
bark or leaves that have been shredded into long
fibers. These fibers
are bunched together and tied in the middle.
The bundles are then nailed
down between two long pieces of wood or bamboo and floated
just under the
water surface, with the ends hanging down into the
water. This will
look like the roots of water plants to the fish.
<FIGURE>
12p132.gif (486x486)
A kakaban is better to use for carp breeding than plants
because it can be
boiled and sterilized each time it is used.
This will prevent any fungus
or bacteria from attacking the newly-laid eggs.
TILAPIA -- Spawning in Nature
Tilapia spawn every month or so, as long as the water is
warm. The male
begins the reproductive behavior by digging holes in the
pond bottom
or side wall about 35cm across and 6cm deep.
<FIGURE>
12p133a.gif (486x486)
The female will deposit her eggs, about 75 to 200 of them,
in the nest,
and then the male releases his milt.
The female picks up the eggs and
the milt in her mouth, so the fertilization of the eggs of
actually takes
place in the females' mouth.
Tilapia often are called "mouth breeders."
The eggs remain in the female's mouth until they hatch -- 3
to 5 days.
Then the fry stay in the female's mouth until the yolk sac
is gone.
During this time, the female does not eat.
As the fry grow, they continue to hide in the mother's mouth
when they
are threatened. The
main reason for this mouth-breeding is for protection
of the young fish, since the tilapia have relatively few
eggs
compared to some other pond fish.
Tilapia is also a favorite food for
a number of predators.
Because the fry are so well taken care of by the
mother (and even sometimes by the father fish), these young
fish are
easier to raise than some other species of fry.
<FIGURE>
12p133b.gif (486x486)
TILAPIA -- Spawning in Ponds
Tilapia spawn well in ponds.
It takes no special equipment or ponds.
A tilapia needs only a pond with a loose bottom to
spawn. The spawning
ponds can be stocked with 25-30 females per [100m.sup.2]
(1/100 ha) and about
40-45 males. If the
temperature is warm enough, the males will begin
digging holes in the pond bottom immediately, and the female
will be
attracted to the hole and release her eggs.
From that point, spawning
continues as in nature.
<FIGURE>
12p134.gif (486x486)
Tilapia will also spawn in ponds that do not have loose
bottoms. In
these ponds, place large-mouth pottery jars or wooden boxes
on their
sides on the pond bottom; the tilapia will use these
containers as nests.
Young tilapia mature at about 3 months, when they are only 6
to 10cm
long. They can then
breed every 3 to 6 weeks, as long as the water is
warm. In areas near
the equator where the water is always warm, tilapia
can breed almost continuously.
When a fish begins to breed, his energy goes into the
development of his
reproductive organs, not into bodily growth.
The main problem with
breeding tilapia in fish ponds, therefore, is the rapid
reproduction of
this fish.
Reproduction can be controlled by sorting the tilapia by sex
and placing them into separate ponds, or by producing a
monosex culture
by hybrid crossing.
However, these methods can usually be done only by
large commercial or government hatcheries where conditions
are controlled.
The problem of fast breeding in tilapia ponds can also be
controlled by
using some natural predators of tilapia in the pond.
The predators most
often used are catfishes of the genus Clarias and,
sometimes, eels like
Anguilla japonica, and some other carnivorous fishes like
Serranochromis
robustus, in a polyculture with tilapia that are
reproducing. These
predators will eat the young fry, allowing the adult fish to
continue
their growth by having no competition for the available
food.
CHINESE CARP -- Spawning in Nature
Chinese carp spawn in the large rivers of China when the
spring rains
cause the water levels of the river to rise.
The eggs are found
drifting down the rivers with the current, and they are
collected by
fry dealers as they drift.
The main requirements for hatching Chinese
carp eggs are a swift current and plenty of oxygen.
Not much is
known about their breeding habits in nature, but they are
likely to
show normal chasing behavior and then spawn, like common
carp. Most
Chinese carp are cultured by collecting their fry and eggs
from the
rivers in the spawning season.
<FIGURE>
12p135a.gif (437x437)
CHINESE CARP -- Spawning in Ponds
The Chinese carp are all annual breeders.
Good brood stock is chosen
in the same way as breeders of common carp.
Chinese carp breeders
usually are kept in small ponds, separated by sex.
When they are
sexually mature, it is quite easy to tell them apart, since
the males
will usually leak milt when handled, and develop other body
changes such
as serrations (rough edges) on their fins.
<FIGURE>
12p135b.gif (486x486)
Chinese carp brood stock must be well cared for, like all
brood stock.
They must be allowed to live undisturbed until time for
spawning. However,
the Chinese carp must be induced to spawn (see Induced
Spawning).
<FIGURE>
12p135c.gif (486x486)
INDIAN CARP -- Spawning in Nature
The Indian major carp will not spawn in standing water, so
special ponds
are built in India to provide a flow of water for these
fish. These
ponds are built like barrage ponds in upland areas so that
the water
flows through them.
But these ponds are impossible to build in many
locations, so the Indian carp often are bred by induced
spawning.
In nature, the Indian carp spawn in rivers like the Chinese
carp. The
eggs are then collected and transferred to hatching ponds.
<FIGURE>
12p136.gif (486x486)
INDIAN CARP -- Spawning in Ponds
Good Indian carp breeders are sexually mature when milt
comes from the
male as it is pressed on the stomach.
Ripe females have soft, rounded
bulging abdomens and reddish genital openings.
The breeders should
be kept separated by sex in ponds prior to the breeding
season, so that
they will readily spawn when introduced into the breeding
hapas.
Usually one female is placed into a hapa with two males to
insure that
fertilization occurs.
If a farmer can place the breeding hapa into
a source of flowing water, he may be able to breed these
fish naturally.
If not, Indian carp must be bred with induced spawning
methods.
A hapa is a rectangular box about 1m in depth and 1.6 -
[6.5m.sup.2] in surface
area. It can be made
from mosquito netting with a mesh size of
3mm. Hapas can be
made in many sizes. Some other
dimensions of hapas
used in Indian carp culture are:
91cm x 91cm x 183cm
91cm x 122cm x 244cm
91cm x 152cm x 305cm
91cm x 183cm x 366cm
<FIGURE>
12p137a.gif (486x486)
The hapa is held in place inside the 'pond with stakes of
bamboo or other
wood. The breeders
are put inside the hapa. Kakabans are
placed below
the water surface, and the top of the hapa is closed so that
the
breeders do not escape while mating.
After spawning, the kakabans can
be removed and taken to the nursery pond and the breeders
released into
the pond. Hapas can
be used to spawn other fish as well.
THE GOURAMI -- Spawning in Nature and Ponds
The gourami build nests out of plant materials to lay their
eggs. The
eggs hatch in about 30 hours.
The fry float belly-up for 5 days until
feeding begins. The
gourami can spawn all year round in warm water
conditions.
<FIGURE>
12p137b.gif (486x486)
This is a very good pond fish, and very easy to breed as
long as you
have a well-fed brood stock.
The natural food of the gourami is soft
leaves of plants like Colocasia and Carica.
They can also be fed rice
bran before breeding.
Usually 10 females and 5 males are stocked in
ponds as small as [100m.sup.2] and the eggs float until they
hatch.
Breeding in ponds is done by merely placing the breeders
together in a
pond where there are some marginal plants available for nest
building.
Once the fry hatch and begin to feed, they can be stocked in
nursery
ponds.
OTHER GOURAMIS -- Spawning in Nature and Ponds
The snakeskin gourami and the three spot gourami build nests
made of air
bubbles so that their eggs float.
The kissing gourami scatters its eggs,
which are free-floating.
<FIGURE>
12p138a.gif (486x486)
To breed the snakeskin and three spot gourami, place the
ripe fish into
a well-oxygenated pond that has a good growth of aquatic
vegetation,
particularly Hydrilla verticillata.
These fish will continue to spawn
as long as the water temperature stays at 26 - 28 [degrees]
C. Hatching takes
place about 2 days after spawning, and the fry absorb the
yolk sac
within 3 to 7 days.
The kissing gourami spawn at 6-month intervals and spawn
within 18 hours
of stocking in the pond.
Some of the eggs may be eaten by the parent
fish, so there must always be abundant vegetation in the
spawning pond
to prevent this. The
eggs hatch in 2 days and float on the surface for
3 to 4 days. The new
fry eat the decaying plants and plankton in the
pond.
CLARIAS CATFISH -- Spawning in Nature and Ponds
Clarias macrocephalus spawns during the rainy season in
nests on the
bottom of natural waterways, while Clarias batrachus spawns
in horizontal
holes in the banks.
Hatching takes place after 20 hours at 25 - 32 [degrees] C.
The fry are then collected by hand net from the nests.
There are
2,000 to 15,000 fry in each nest.
Clarias catfish will spawn naturally in ponds, but induced
spawning
methods may be used if necessary.
<FIGURE>
12p138b.gif (486x486)
THE TAWES -- Spawning in Nature and Ponds
The tawes spawn in the rainy season.
Tawes ponds usually are about
200 to [500m.sup.2] and about 50cm deep.
The ponds should be dried for 5
days before they are filled, and the spawners should be
introduced when
the pond is half full.
Tawes need well-oxygenated water that has a strong
current to spawn.
Mating occurs at night; then the current should be
turned off and the eggs spread out evenly on the pond
bottom. The eggs
hatch in two to three days.
After 20 days, the fry can withstand the
current, and it should be turned on again.
Tawes females produce
about 20,000 fry each.
<FIGURE>
12p139a.gif (486x486)
HETEROTIS NILOTICUS -- Spawning in Nature and Ponds
This species is normally light-colored, but during the
breeding season
it changes to dark brown.
The spawning of Heterotis niloticus in
nature begins at the end of the dry season when water is
very warm.
The fish splash in the shallow water among the weeds in the
ponds to
begin their breeding behavior.
Then the male builds a nest of weeds
in water that is 10 - 45cm deep.
The nest is made in a depression
that is 15cm deep and 60 - 100cm wide.
The nest has a grass wall at
its outer edge which keeps other fish out of the nest.
To get in and
out of the nest, Heterotis niloticus jumps over this wall.
<FIGURE>
12p139b.gif (486x486)
The eggs of Heterotis are about 3mm in diameter, and are
laid in the
bottom of the nest and then fertilized.
One of the parent fish is
always in the nest to circulate water over the eggs (to give
them
oxygen). The eggs
hatch in 4 - 5 days. The fry travel in
a "school"
and stay with their parent fish for several months after
hatching.
The fry are very delicate, and should not be handled for a
while.
EELS -- Spawning in Nature and Ponds
The eels used in Taiwan (Anguilla japonica) spawn in the
sea, and
the fry (called elvers) swim upstream where they are
collected by dealers.
Eels, are stocked in rates of up to 25,000 fry/ha along with
other fishes,
and must be fed supplementary feeds like pellets of trash
fish. It is
not recommended that a beginner work with eels because they
must be fed
protein and are not very efficient converters of food.
Eels cannot be bred in ponds.
<FIGURE>
12p140a.gif (486x486)
MILKFISH -- Spawning in Nature and Ponds
Milkfish spawn in saltwater during the rainy season.
The fry are caught
along the shore line at breeding season (which corresponds
to the
rainy season) and then transferred and acclimatized to
freshwater ponds.
This is done for the most part in the Philippines and in
some other
Southeast Asian countries like Indonesia and Taiwan.
Milkfish cannot be bred in ponds.
<FIGURE>
12p140b.gif (486x486)
STRIPED MULLET -- Spawning in Nature and Ponds
The striped mullet is a saltwater fish, and spawns in the
sea. The
fry are collected as they swim upstream.
The mullet can be induced to spawn by hormone injection, but
this is
very difficult and certainly is not recommended for a small
fish pond
owner.
Induced Spawning.
Induced spawning means making the fish produce eggs
an milt when they will not do so naturally.
Induced spawning is done
when the pond conditions cannot be made to encourage natural
spawning,
or when the fish are not ready to spawn when the farmer
wants them to
spawn.
Spawning can be done by three methods:
*
hormone injection
*
hormone injection with stripping
*
stripping
Each of these methods has advantages and disadvantages.
Hormone Injection.
Hormone injection is the most common method of
induced spawning, and it requires certain kinds of
equipment:
*
hypodermic needle and syringe
*
mortar and pestle
*
saline solution or distilled water
*
centrifuge
*
test tubes
*
dissecting kit
<FIGURE>
12p141.gif (486x486)
This technique uses the pituitary gland (the hypophysis) of
the fish.
This gland contains the substances(hormones) that trigger
the reproductive
organs of the fish to start developing.
When these hormones are
taken from a ripe fish and injected into a fish that is
ripe, but has
been unable to spawn, the injected fish will spawn in 6 - 12
hours.
The ripe fish must be killed to get the pituitary gland
out. This must
be done very carefully.
The gland is very small: less
than 1mm in
diameter in the common carp, which has a relatively large
pituitary.
The pituitary gland is a round, yellowish-red organ located
in the brain
pan of the fish.
Here is the method commonly used to take the gland
from the fish:
*
Use a mallet or dull knife.
*
Hold the fish near the head with one hand.
*
Hit the fish above the eyes at the point
where the skull begins.
This will kill the fish.
*
Make sure to hit straight and up a
little. A solid hit should
dislodge the
skull.
*
Slit the skin around the front and sides of
the skull, then lift
up the top of
the skull and fold it back as if it were a hinge.
The brain is
attached to the top of the skull; by folding it back,
the underside
of the brain is exposed. The pituitary
gland is located
in the middle
part of the underside of the brain.
If located in this way, the pituitary gland is relatively
easy to
find. However, this
must be done carefully. If the skin is
cut too
much, or the fish is handled too much, the contents of the
brain will
move and the pituitary will be hard to locate.
The brain contains a
number of fat deposits which are yellowish and could easily
be confused
with a pituitary by someone who was not familiar with that
gland.
Most farmers will not be interested in doing hormone
injection spawning.
But you should be familiar with and be able to do it.
Steps for
processing the pituitary gland and giving the injection are
given below:
*
Select the fish you want to spawn and weigh
them.
*
Select the fish that will be killed for
their glands and weigh
them.
Always match the weights of the donor and
recipient
fish.
If a donor is 1.5kg and the recipient is
3kg, use pituitaries
from two 1.5kg
donors.
*
Kill the fish, as outlined above.
*
Remove the pituitary from the fish matching
weights (or use
2 to 3mg of dried
pituitary gland for every kilogram of body
weight.)
*
Place the pituitary gland into the mortar.
*
Grind the pituitary with pestle until it is
a pulpy mass.
*
Wash the pituitary into a test tube with 1
milliliter distilled
water or
saline solution.
*
Place the test tubes into the centrifuge.
*
Centrifuge the glands for 5 minutes.
*
Remove the test tubes from the centrifuge.
*
Draw up the liquid portion from the test
tube into the
hypodermic
needle, leaving the pulp of the gland in the
bottom of the
test tube.
<FIGURE>
12p143.gif (486x486)
*
Inject the fish above the lateral line
behind the
dorsal fin,
just underneath the scale.
*
Place breeders into the breeding pond.
All of the materials used in hypophysation can be found or
made
easily. A simple
centrifuge can be constructed very easily from a
hand drill (see next page for instructions).
If a centrifuge cannot
be found or made, the fish may be injected with a whole pituary
gland.
The gland may be dropped into the syringe, water added, and
injected
into the fish as outlined above.
The force needed to push the gland
out through the needle will crush the gland as if it were
being ground
with the mortar and pestle, and this will allow the hormones
to be
released.
After the injection, the female fish will begin to develop
her eggs
until they are ready for fertilization by the male.
In some fish, it
is necessary to inject the female twice with varying amounts
of
pituitary extract (see Chinese carp) and the male,
once. After the
injections, the fish are treated in the same way as in
natural
spawning.
MAKING A CENTRIFUGE
Tools and Materials:
*
1 hand drill
*
1 20cm piece small wood (or bamboo) dowel
rod
*
2 metal cigar tubes (or plastic, or rubber
hose with clamps)
*
2 pieces medium wire (long enough to wind
around the tubes 6
or 7 times)
*
1 piece heavy wire about 9cm long (old coat
hanger will work)
cotton balls
or pieces of soft material
*
2 test tubes or small clean glass bottles
*
string, tape, and nylon fishing line
<FIGURE>
12p144.gif (486x486)
Construction Steps:
*
Drill hole through one end of dowel rod
about 1cm from the
end.
*
Remove drill bit from drill.
*
Insert dowel rod into drill bit hole,
leaving end with newly
drilled hole
at opposite end on top.
*
Insert piece of heavy wire through the hole
in dowel rod.
*
Bend the ends of the wire into loops.
*
Secure the wire on either side of the dowel
rod with tape
to keep the
wire from slipping through the dowel rod hole.
*
Wind medium wire around each cigar tube
leaving about 2.5cm
of wire free
at the top of each tube.
*
Attach tubes to heavy wire by bending medium
wire (left
over from step
just completed).
*
Place a small cotton ball in the bottom of
each tube to
cushion the
test tubes.
Stripping. Stripping
is the term given to the method of actually
pushing eggs and sperm out of the fish and mixing them in a
dish. This
can be dangerous to the fish, mostly because the fish can be
hurt by
pressing on the belly.
Stripping is especially dangerous to a fish which
is not ready to spawn.
If the fish is ready to spawn, a gentle stroking
motion down the side of the fish towards the genital opening
will be
enough to release the eggs or sperm.
<FIGURE>
12p145.gif (486x486)
First the eggs are stripped into a dry dish.
Then the milt is stripped
into the same dish.
Mix the eggs and milt gently with a feather.
Add
water to the dish so that fertilization can occur.
After a few hours
and a few changes of water in the dish (to provide eggs with
oxyqen),
transfer the fertilized eggs to the kakabans and allow them
to hatch
as normal.
There are other variations of stripping that are worse than
the one
outlined above. One
method involves killing the female or male, or
both, and removing their reproductive organs and then mixing
the eggs
and sperm by hand.
Not only is it necessary to kill both breeders, but
if the eggs and sperm are not ripe (mature) and ready for
fertilization,
no fry will hatch.
Stripping with Injection.
Often stripping is done after the fish have
been injected with hormone extract.
The fish are injected, and the
eggs are allowed to develop.
Then the fish are stripped into a dry
dish, etc. Stripping
with injections works fairly well. But
of the
three methods of induced spawning described here, the best
is just
to inject the fish and let them spawn by themselves in the
pond. The
following paragraphs give directions for induced spawning of
some
important pond fish.
INDUCED SPAWNING OF CHINESE CARP
The Chinese carp must be induced to spawn by hormone
injection. The
normal dosages for bighead, black, mud, and silver carp are
2 to 3mg
of dried pituitary or 3 fresh pituitary glands for every
kilogram of
female fish. That
is, if the female silver carp weighs 2.5kg, 5mg of
dry pituitary or 6 fresh pituitary glands are needed to
ripen her eggs.
Or HCG (human chorionic gonadotropin) can be used at dosages
of 700 to
1000 IU (international units) per kilogram.
But HCG is expensive and
certainly not available to everyone.
Grass carp need higher dosages
(3 to 4mg dried pituitary per kilogram of body weight).
Inject only
a fraction (1/10 to 1/4) of the total for the first dose;
then, follow
it with the rest of the dose, 6 - 24 hours later.
After injection, put the breeders into the breeding
pond. The temperature
should be about 23 - 29 [degrees] C to encourage spawning, and
the oxygen
content should be at least 4ppm.
It is best to put in two males for
every female. Let
the fish spawn on their own; they will spawn within
a day. Remove the
breeders after spawning.
Hatching Chinese carp is complicated.
Chinese carp eggs need a constant
supply of clean, well-oxygenated water flowing from the
bottom up
through the eggs to stimulate hatching.
Some types of hatching
bags have been developed for this purpose.
One kind of bag hangs from a
rack down into the nursery pond or a trough, and water is
bubbled up by
pipes from the inflow pipe.
These bags have an advantage in that once
the fry are hatched, they can easily be transferred without
touching
them at all. This is
good, because Chinese carp fry are very sensitive
to handling stress.
<FIGURE>
12p147.gif (486x486)
After the carp spawn, the eggs are collected by net or by
draining
the breeding pond, and they are placed in the hatching bags
(or
shallow trays) as soon as they have hardened after
ferlization (1 to
2 hours). The eggs
hatch in 1 - 2 days depending on the temperature,
and then absorb their yolk sacs in another 3 - 6 days.
As soon as the fry absorb their yolk sacs, they should be
transferred
in the hatching bags to nursery ponds.
The nursery ponds should be 0.5
to 1.0m in depth and the oxygen level should be at least
4ppm for good
fry growth.
The spawning of Chinese carp is a very complicated business
and is usually
done inside carp hatcheries so that all conditions can be
controlled.
In China, the carp hatcheries sell their fry to fish pond
owners who
then raise them to marketable size.
For most farmers, common carp is
a much easier fish to work with and is just as valuable for
food as
are Chinese carp.
INDUCED SPAWNING OF CLARIAS CATFISH
The Clarias macrocephalus fishes are injected with pituitary
extract at
a rate of 13 to 26mg/kg at 25 - 32 [degrees] C.
Spawning occurs within 16 hours.
Larvae (fry) absorb the yolk sac in 5 days, and are
transferred and reared
in ponds only 18cm deep.
The best food for fry is zooplankton, but
after 2 to 3 weeks, trash fish may be added.
They can be fed rice bran
as well, and later on a mixture of trash fish, rice bran,
and broken
ice. In Thailand
this sort of production gives yields of 97,000 kg/ha
per year. Clarias
catfish are used in fish ponds throughout Southeast
Asia now, and are enjoyed for their good taste.
INDUCED SPAWNING OF INDIAN CARP
If you cannot build a fish pond like a barrage pond or spawn
the Indian
carp naturally in ponds, they can also be induced to spawn
by hormone
injection but this is very difficult to do.
Induced spawning is
dependent on the dosage and the stage of maturity of
the breeders.
Breeders should be about 2 to 4 years old, and weigh 1.5 to
5.0 kg.
Females are injected twice, once with 2 to 3 mg of pituitary
gland per
kg body weight, and then, after 6 hours, with 5 to 8
mg/kg. Males
are injected once, at the time females get their second
dose, with a
dose that is equal to the first dose given to the
females. After
the second injection, the fish are placed together in
breeding "hapas"
and spawning takes place within 3 to 6 hours.
The breeders are put
inside the hapa, kakabans are placed below the water
surface, and the
top of the hapa is closed so that the breeders do not escape
while
mating. After spawning
the kakabans can be removed and the breeders
released into the pond.
The eggs should be transferred to deep
hatching hapas where they will hatch in 15 to 18 hours at 27
[degrees] C.
However, this induced breeding does not work as well as
Chinese carp
breeding, so most Indian carp fry are still caught and
collected
in natural waters.
INDUCED SPAWNING OF COMMON CARP
Sometimes common carp will not spawn in ponds, and they are
injected.
The amounts needed for common carp are determined by the
fishes' weight.
Usually the common carp is injected only once with pituitary
extract
from a fish that has the same weight as the injected
fish. The male
is not injected.
After the injection, the fish are placed into the
breeding pond.
Usually a good female breeder will weigh 1 to 2 kg.
This one large female is placed with 1 or 2 males, so that
the
total weight of the males is approximately the weight of the
female.
If you have a female of 2 kg, you can use two males of 1kg
each.
The more males, the greater the chance that fertilization
will occur.
If you have a large breeding pond, you can place about 5 or
6 large
female fish and 10-15 males to insure that all the eggs are
fertilized.
Carp will only respond to pituitary injections from other
carp. However,
many other fish will respond to the pituitary gland of
common carp, so
often carp are kept just to serve as donors of this gland in
other
induced spawning attempts.
Also, carp glands are relatively large
and easy to find, compared to the glands of other fishes,
and can be
stored for later use by drying, freezing, or powdering.
Carp glands
can be preserved by placing them in 100% dry acetone, then
cooling
them by placing that jar they are placed in, into an ice
bath. Every
12 hours, the acetone should be changed, for a total of four
times.
Then the pituitaries are air-dried, and stored in an
air-tight
container. This is
called the alcohol drying method; glands preserved
in this way can still be used after 10 years!
7
Harvesting Fish
Harvesting is the collection of fish from a pond for sale at
market,
or for cooking and preservation for family use.
Harvesting can refer
to collecting all the fish or to taking out only some of the
fish
(this happens often in tilapia ponds having both young and
adult fish).
If the pond can be drained, harvest the fish by draining the
pond into
the catch basin and collecting the fish with a scoop
net. If the pond
cannot be drained, drain out as much water as possible and
use a series
of nets to catch the fish.
Types of Nets
There are different kinds of nets which can be used in
ponds. Some nets,
such as the one shown here are gill nets.
Gill nets often have mesh
sizes from 2-3cm; they are often used to harvest the largest
fish in a
pond and leave the smaller fish until they grow larger.
<FIGURE>
12p149.gif (486x486)
They are called gill nets because the
fish pokes his head through the net
mesh, and is caught around the gills as
he tries to wiggle through the net.
Another net used to harvest fish is the seine.
A seine can collect all
the fish in the pond at one time because it has smaller
openings (mesh
size) than the gill nets, and it is usually made of heavier
fibers to
hold the fish. (See
the end of this section for instructions on making
a seine.)
<FIGURE>
12p150a.gif (437x437)
Both seines and gill nets have lead sinkers (weights)
attached to the
bottom ropes. These
weights hold the nets at the bottom of the pond
(so the fish cannot escape underneath the nets as they are
pulled).
Seines and gill nets also have floats attached to the top
ropes to help
the net form an enclosure:
the entire pond is netted with one sweep
of the net.
Netting a Pond
Let out as much water as possible.
NEVER LET THE WATER OUT COMPLETELY.
As the fish have less and less water in which to live, they
become
excited and use up more oxygen when there is less
available. Plan on
harvesting while the water is draining out so the fish are
caught before
they are stressed.
Or, drain the pond almost completely, and then let
water slowly trickle through while netting the fish.
<FIGURE>
12p150b.gif (486x486)
12p151a.gif (486x486)
<FIGURE>
USING A SEINE Place
the net at one end of the pond and slowly draw
the edges down the sides of the pond.
Bring the middle of the net
across the pond.
When near the other side, begin
pulling the edges up onto the bank
so that the net forms a u-shape in
the pond. Pull up
the bottom
rope of the net along the pond
bottom until it breaks the water
surface. At this
point the net
is a bag shape and will hold the
fish in (some seines already have
a bag woven into them).
<FIGURE>
12p151b.gif (486x486)
Pick the fish up one by one and transfer them to buckets or
tubs of
clear water for later weighing and transport.
<FIGURE>
12p152.gif (486x486)
OTHER HARVESTING METHODS
Fish also can be harvested by other
methods. One method
is to catch them with a hook and a line, but this
method is time-consuming.
In some parts of the world fish are harvested
by dynamiting or poisoning the water.
But these methods are dangerous
and should never be done in a pond or any other
waterway: dynamite
and poisons can kill people and other animals, in addition
to fish.
NEVER HARVEST FISH BY DYNAMITING OR POISONING THE POND.
There are
easier and cheaper methods than these.
Marketing Harvested Fish
Once fish are harvested, they must be marketed.
Marketing includes the
transportation and sale of fish.
As the introduction to the manual
pointed out, one very important thing to consider before
building a
pond is the availability of a market.
If a market is further away,
the farmer must have transportation to it over passable
roads. If the
market is very near, he may want to advertise the date of
his harvest
by word-of-mouth so that the people will come directly to
the pond to
buy the fish. Also,
he may want to make an agreement with a tradesman
at the market so that he is sure he has a buyer for his fish
when they
are harvested. If
there is no market, or if the farmer is going to use
all the fish himself, then he probably will want to preserve
some of the
fish (see fish preservation).
Containers for storing
live fish being taken
to market.
<FIGURE>
12p153.gif (393x393)
Transporting fresh fish to market must be carefully done, so
that the fish
are not damaged.
Usually, fish are handled in the same way they were
handled when put into the pond.
If it is not possible to get the fish to
market right away, they must be preserved -- either on ice
for quick sale
in a nearby market; or salted, dried, smoked, or canned if
going to a
distant market.
These methods are discussed in the next section.
Remember: Fish spoil
very quickly in warm temperatures. Sell
or preserve
the fish right after harvesting.
After Harvest
After the pond is harvested, it should be prepared for the
next stocking
of fish:
*
Plow the bottom of the pond
*
Clear out predators, sticks, rocks, etc.
*
Dry the pond bottom until the soil cracks
*
Put lime on the pond bottom
*
Wait two weeks
*
Add water to the pond
*
Check the water quality
*
Put new fish into the pond
*
Begin daily and monthly management of fish
and ponds
*
Breed
*
Market
*
Harvest
*
Begin again
<FIGURE>
12p154.gif (437x437)
MAKING A SEINE
A seine can be made using materials found in the
market. The materials
needed are:
*
rope
*
cork floats
*
lead sinkers (or-something heavy to help the net sink)
*
netting
*
sewing needle for nets
The directions for making the net are as follows:
*
Tie a rope that will be used for the top and
bottom lines
between two
trees. Use nylon rope, if possible,
because it
will last
longer than cotton or hemp.
*
Mark each rope at 15cm intervals.
Make sure the rope is
longer than
the final net by a few meters.
*
Stretch the netting until the meshes close
completely; then
count the
number of meshes in a 23cm section.
Good netting
for a general
seine will have 6 to 9 meshes in a 23cm stretched
section.
<FIGURE>
12p155.gif (437x437)
*
Use nylon string that is very strong.
Wind a long section on
a net
needle. Then tie the end onto the lead
line rope (top
rope) at the
first marking. Pass the needle through
the number
of meshes
counted in the 23cm section of netting.
Tie the
string on the
rope at the second marking.
*
Repeat the process until the last marking on
the top rope is
reached.
*
Pound the sinkers, or string them, onto the
bottom rope at the
15cm
intervals. Tie the cork floats onto the
top rope at the
same intervals.
*
String the bottom line onto the netting in
the same way as the
top line.
REMEMBER: The net
must be washed, repaired, dried in the shade, folded,
and put
away in a cool, dry place after each use.
A net
which is taken
care of in this way will last much longer.
8
Preserving Fish
Fish that are not taken to the market fresh must be
preserved in some way
after harvesting.
All fish have bacteria in their intestines; as soon as
they die, these bacteria begin to multiply, and the process
of decay begins
So the first thing which must be done -- as soon as possible
-- is to remove
the intestines.
After this is done, go on to preserve the fish in
the way chosen.
There are a number of ways to preserve fish:
salting and smoking are
discussed here in some detail.
Salting Fish
Salting is a very old method of preserving fish.
Salting depends on the
size of the fish, the species, and on the amount and quality
of the
salt used. Fish
which have been salted well last a long time without
spoiling.
The most important factor in salting fish is the quality of
the fish
being salted. Use
only fresh fish: fish which have been
lying around
for hours are not good for salting.
Also, use only clean equipment and
clean fish.
PLEASE READ THE DIRECTIONS THROUGH CAREFULLY BEFORE
BEGINNING.
TOOLS AND MATERIALS
*
Clean sharp knife
*
Salt -- about 20kg for each 100kg of fish
*
Containers for washing fish (buckets, tubs,
drums)
*
Flat working surface (table, flat stones)
*
Containers for holding waste (parts of the
fish not used)
<FIGURE>
12p158a.gif (393x393)
*
Waterproof boxes or jars to hold salted fish
(glass or wood;
not metal
unless the metal is stainless steel)
*
Boards and weights (to press down the fish)
*
Slats or lines for drying the fish
*
Small shelter to cover fish while drying
STEPS IN SALTING FISH
There are four major steps:
gutting and cleaning; salting; washing and
drying to remove excess salt; and, finally, air drying.
Gut and Clean the Fish.
<FIGURE>
12p158b.gif (437x437)
*
Gut the fish by cutting along the belly from
the gills to
the anal vent.
*
Remove the guts and the black membrane in
the gut cavity.
*
Cut off the head now, if preferred; it is
not necessary.
*
Bleed the fish by removing the gills and all
blood vessels
after cutting
open the throat.
*
Cut the fish into the right shape for
salting: small fish
may be left
whole; larger fish should be split in half from
head to tail,
so that all the fish flesh will be exposed to
the salt.
<FIGURE>
12p159.gif (486x486)
Salt the Fish.
*
Sprinkle a layer of salt on the bottom of
the container
which will hold
the fish.
*
Place a layer of fish, flesh side up, on the
salt. Do not
let the fish
lay on top of each other.
*
Cover the fish with a thin layer of salt.
*
Continue to place fish, then salt, almost to
the top of
the container.
*
Place the last fish layer with the skin side
up. Sprinkle
with salt; the last layer must be salt.
*
Place boards and weights on top of the fish
in the container
to press them
down.
*
Leave the fish in the container for 15
days. Add salt
as necessary,
until the fish are "struck through" -- thoroughly
full of
salt. As the fish lie in the salt, the
salt draws out
all the moisture in their flesh. This
moisture forms
a solution (brine) with the salt as the
salt
dissolves. It is necessary to add more
salt as the
salt is diluted in the solution.
As the moisture is removed
from the fish
by the salt, the level of fish in the container
falls.
*
Add more fish, skin side up, and also more
layers of salt as
the level of
fish falls.
<FIGURE>
12p160.gif (486x486)
Wash and Dry the Fish.
*
Remove the fish from the container when they
are fully
salted.
The fish are properly salted when they are
firm
and have a
whitish salt layer on their flesh.
*
Wash the fish in clear, clean, sea water or
brine.
*
Place the fish on a flat surface and press
them down with
boards and
weights to make them as flat as possible before
drying.
Air Dry the Fish.
*
Dry the fish in the sun and in the air, or
use heating and
fans.
Usually fish are dried outside in an area
that is
exposed to sun
and wind and is very clean.
*
Dry the fish under a shelter of leaves or
branches for the
first few days,
so that they do not dry too quickly.
<FIGURE>
12p161a.gif (486x486)
*
Put the fish into as much sunlight as
possible, after the
first few days.
*
Lay the fish on triangular slats or hang the
fish by their
tails from fish
lines strung up between trees.
<FIGURE>
12p161b.gif (486x486)
*
Cover the fish if it rains.
Any moisture at all, at this
stage in the
salting process, will cause the fish to spoil.
*
Dry the fish for about six days.
*
Pack and store the fish in waterproof
containers.
HOW TO USE SALTED FISH
Soak salted fish in fresh water overnight.
Change the water at least once
during this time.
The soaking removes the salt; the longer the fish is
soaked, the more salt is removed.
After the fish has been soaked, it can
be used in any way that fresh fish is used.
Smoking Fish
Smoked fish does not last as long as salted fish, because it
must be refrigerated,
frozen, or canned if it is to be stored.
Smoked fish are prepared
in a smoke house which is merely a shed or a box over a fire
which
is controlled so that it produces smoke instead of
flames. The fish are
merely hung inside the smokehouse so that they are
surrounded by smoke.
It takes about six hours to smoke fish so that they can be
eaten or stored.
Smoked fish are prepared like fish for salting.
After they are bled, and
gutted, they are split from head to tail.
They are then washed in freshwater
and placed in a saltwater brine made by dissolving 1kg of
salt in one liter
of water for one hour.
Then the fish are removed from the brine and washed
in clean, fresh, water again.
The fish are then drained and hung in a cool
breezy place for about an hour.
<FIGURE>
12p162.gif (486x486)
At this point, the fire can be
built in the smokehouse.
When
it is smoking properly, place
the fish on hooks and hang
(or tie) the fish in the top
of the smokehouse.
Make sure
the fish are placed securely
so they will not fall.
Watch
the fire carefully to make
sure it is smoking, and not
burning, the fish.
After the fish are smoked for
six hours, they can be eaten
immediately, or stored in jars
(to be canned), or stored frozen
or refrigerated until they
are eaten.
Smoked fish do not last as long as salted fish, so do not
smoke all of the
fish, unless it will be used soon after harvesting.
Other Preserving Methods
Fish can also be preserved by simple air drying, or by
canning. Air
drying involves only cleaning and washing the fish and
drying them in
the sun and wind until they are a clear white color.
Canning is a much
more complicated process.
Canning must be done very carefully:
fish
can contain many bacteria which must be killed before
canning. If fish
are canned with this bacteria still in them, the fish will
spoil. People
who eat canned fish which is spoiled can become very
sick. A farmer who
wishes to can his fish should arrange with a canning factory
to take part
of his harvest and can it for him.
A farmer should not try to can fish
at home unless he has expert help.
Often fish are preserved by freezing.
Freezing requires a constant
supply of electricity -- which most farmers do not
have. If electricity
is available, however, freezing is one of the easiest and
safest ways
to preserve fish. In
this method, the fish are gutted, cleaned, cut
up (if desired), placed into containers, and put into
freezers. Frozen
fish can last for a very long time, if they are not thawed
(unfrozen).
Once frozen fish are thawed, they must be used immediately,
or they will
spoil.
Spoiled Fish
Even spoiled fish can be used -- although it cannot be eaten
by human
beings. Spoiled fish
can be cut up and boiled, then dried in the sun or
cooked in an oven until it is very flaky.
Once this is done, grind the
fish into a powder and mix it with powders of plants:
this makes a very
nutritious food for fish in ponds.
The powder can be used as a powder,
or it can be mixed with something to make it stick together
so that the
powder can be pressed into pellets for fish.
Spoiled fish, and even the guts of fish that have been used
in some other
way, are called "trash" fish.
The powder is called "fish
meal." Fish
meal is used to feed fingerlings or even brood stock.
Fish meal is one
of the best fish foods for pond fish.
9 Problems
of Fish in Ponds
Fish cultured in ponds can have problems:
they can be stressed by a
lack of oxygen; they can be eaten by predators; they can be
infested by
parasites. These
problems and some solutions to these problems are
discussed in this section.
Diseases
Diseases of pond fish are caused by fungi, bacteria,
protozoans, worms,
and crustaceans.
Usually diseases can be controlled by proper pond
management, which includes draining the pond, drying it, and
liming it
periodically, and also by preventing wild fish or unfiltered
water from
entering the pond.
Some diseases are fatal, but many can be controlled
by treating the pond or the fish with chemicals.
Some diseases attack fish in ponds because some other factor
is causing
stress:
overcrowding, low oxygen levels, or not enough food.
All of
these conditions weaken the fish so they can get diseases
more easily.
The farmer must watch his fish for signs of stress and
disease. Any
change in normal behavior may be a sign of disease; for
example, gasping
at the surface for air, rubbing the body or head against the
sides of
the pond, or ragged fins and sores on the body.
Something is wrong when
a fish population stops eating suddenly.
So the farmer must check the
fish often (see "Management"), especially in very
hot weather.
FUNGAL DISEASES
These diseases are caused by fungi.
Gill Rot. This is a
disease caused by the filamentous fungus, Branchiomyces
sanguinis. This
disease is first noticed by a red spotting on the
gills. Later, the
gills become greyish-white and stop working.
When the
gills stop working, the fish suffocate and die.
Gill rot is most common
during the hot part of the year and is sometimes associated
with large
amounts of dung and a "bloom" of plankton.
Treatment:
Remove dead fish from the pond; the
remaining fish
will probably recover. Drain the
pond and dry the
bottom. Treat the pond with
quicklime or copper
sulphate to kill the fungus spores.
Fill the pond
again. Add quicklime every few
weeks until there
is
no more sign of the disease.
<FIGURE>
12p166.gif (486x486)
Saprolegnia. This
fungus is often associated with Gill Rot.
It attacks
weakened places (e.g., bruises from handling) on fish.
Since it hits
already weakened fish, Saprolegnia attacks fish already
trying to fight
other diseases.
Saprolegnia looks like fuzzy, white cotton wool and is
often in tufts on the body of the fish.
Saprolegnia by itself can kill
eggs and fry, but does not kill adult fish.
Indian carp are very susceptible
to this disease, and common carp eggs are attacked
frequently.
Treatment:
Use the same treatment as outlined for Gill
Rot.
BACTERIAL DISEASES
These are caused by parasites which are
actually bacteria.
Furunculosis. This
is the most important bacterial disease.
This disease
causes-ulcers or abcesses in muscle tissue.
It then breaks through
the skin, and, eventually, becomes a site for fungus
infections, like
Saprolegnia. This
disease attacks in the spring, and is most often found
in more temperate species, like trout.
Treatment:
Drain the pond and treat it with slaked lime.
Disinfect every tool used in the pond (nets,
feeding rings, etc.).
Infectious Dropsy.
This is caused by the bacterium, Pseudomonas punctata.
The symptoms are a swelling of the fishes' belly with water,
ulcers on
the skin, lengthening of the fins, and deformation of the
backbone.
Treatment:
Prevent diseased fish from entering the
pond.
Bury and burn the dead fish.
Columnaris. This is
another bacterial disease which causes discolored
patches on the body, loss of scales, and, often, death.
This disease
can look like a fungal disease, but it is not.
If possible, it should
be examined under the microscope for positive
identification. It is
caused by the bacteria Chondrococcus columnaris and
Cytophaga columnaris
and is often associated with low oxygen levels.
Treatment:
Give fish a feed which has terramycin in
it. If
it
is very bad, place each infected fish in a dip
(bath) of copper sulfate (2 minutes in a solution
of
1 to 2,000) or a dip of malachite green (10 to
30
seconds in a solution of I to 15,000).
Treat
the
pond with 1 ppm of copper sulfate.
PROTOZOAN DISEASES
<FIGURE>
12p167.gif (486x486)
Ichthyophthirius multifilis.
This is the worst protozoan disease.
The
"ich" disease is caused by a ciliate which forms
white spots or pimples
on the skin and fins of the fish.
Each parasite produces thousands of
spores, which can then infect other fish in the pond.
Treatment:
Drain the pond, and lime it.
Or treat the fish
with chemicals as follows:
Formalin
200-250ppm daily bath
15ppm
in pond
Malachite green
1.25ppm
daily bath/30 minutes
0.5ppm
in pond
Methylene blue
2ppm daily bath
Acriflavin
10ppm
3-20 daily baths
Salt
7,000ppm several daily baths
Costia and Trichodina.
These are two other ciliate diseases.
They are
cause by microscopic organisms which attack the skin of fish
and cause
lesions. Tilapia,
the very resistant fish, are attacked by the Trichodina
protozoan.
<FIGURE>
12p168.gif (486x486)
These ciliates cannot be seen by the naked eye, but the
lesions and sores
that they cause can be seen by looking closely at the fish.
Treatment:
Add 3ppm of potassium permanganate to
pond. Or dip
the
fish in baths of 5 to 10% sodium chloride (salt)
for
5 to 20 minutes daily for up to one week.
CRUSTACEAN PARASITES
Lernea. The anchor
worm is the most common disease of this type (a copepod).
This worm attacks the gills or any other part of the
body. It burrows into
the fish, leaving its two egg cases protruding on the
outside of the fish.
Lernea causes red sores, and makes the fish thin so that
their market
value is much lower.
<FIGURE>
12p169a.gif (437x437)
Treatment:
Add castor oil in a thin film over the
surface of
the
pond. Treat fish infected with young
Lernea
in
a formalin bath, or remove each parasite by hand.
<FIGURE>
12p169b.gif (486x486)
Arqulus. Argulus is
the fish louse. It is a flat,
pinkish-red disc
that clings to the skin, fins, mouth, or gills.
It sucks blood with
a piercing organ, which also injects poisons.
Young fish may die.
Treatment:
Drain and lime the pond.
Or place the fish
in
a bath of 3 to 5% salt, or 250ppm of formalin
for
1 hour.
WORM PARASITES Most
of these are external parasites.
Dactylogyrus. This
parasite attacks the gills of young fish.
The fish
are exposed to this worm when they are between 2 and 5cm
long.
Treatment:
Manage the pond well so that fingerlings
grow rapidly past the stage when they are
susceptible to Dactylogyrus.
Gyrodactylus. This
parasite burrows into the blood vessels of fish
through the skin, causing the fish to appear reddish with
sores. This
worm can cause fish to die from emaciation.
Treatment:
Treat ponds with 5 ppm formalin.
Treat fish
individually in a bath of 25ppm formalin.
Bothriocephalus gowkongensis.
This is the tapeworm which often attacks
the Chinese carp, especially grass carp.
It is difficult to treat this
worm; it is found in the fishes intestines.
<FIGURE>
12p170.gif (486x486)
General Treatments
Farmers often will have trouble finding the proper chemicals
for treating
their ponds or deciding which disease the fish have and
which treatment
to give. Here are
some general treatments: any of these
treatments will
help an infected pond.
Baths:
Potassium permanganate
4ppm
Salt 3-5%
Copper
sulfate 500ppm for 1-2
minutes
Formalin 250ppm
for 1 hour
Malachite green 67ppm
for 10-30 seconds
Or the farmer can use unslaked lime directly in the pond.
Some pond owners always treat new brood stock with a
one-hour bath in
10ppm of potassium permanganate, and then transfer the fish
to a bath of
15ppm of formalin for 4 to 12 hours.
This ensures that no parasites will
be introduced into the pond with the brood stock.
Other Problems
Other problems are caused by deficiency or environmental
factors.
Deficiency problems appear because the fish are missing some
factor they
need to grow and be healthy.
The missing factor can be a lack of essential
elements like vitamins or minerals.
This lack is difficult to detect
until a problem exists.
So the only way to prevent this kind of deficiency
is to be sure the fish are eating the right kinds of food.
Environmental problems are caused by some change in the pond
environment
which places a stress on the fish, such as a rapid change in
water
temperature or an increase in pond water acidity.
These are not diseases
but problems of fish in ponds which can be controlled by
watching the
water and soil quality of the fish pond, and by preventing
any rapid
changes from occurring.
<FIGURE>
12p171.gif (486x486)
Predators
Other problems occur in fish ponds when other animals eat
the fish.
Frogs, snakes, and birds eat young fish and must be kept out
of ponds.
The worst predators, of course, are carnivorous fishes, like
the
Clarias catfishes.
Prevent these fish from entering the ponds by
screening the water inlet.
In any pond, all unwanted (trash) fish and predators must be
removed
before stocking the pond.
If the pond can be emptied, simply drain the
pond, plow and dry the bottom, etc.
If the pond cannot be drained, seine
the pond as completely as possible.
However, many fish escape the net by
staying at the edges of the pond.
The best way to get rid of the
predators is to poison the pond water in a pond which cannot
be drained.
USING POISON The
most common poison for use in fish ponds is rotenone.
Rotenone can be purchased -- as a liquid or powder -- or it
can be gotten
from the roots of the derris plant.
To make rotenone, collect derris
roots and pound them until a milky-white fluid can be
squeezed out. This
fluid contains rotenone.
Apply one kilogram of derris root for every
hectare of pond surface area.
If using powdered rotenone, use only 0.05
kg/ha. The powder
should be dissolved in water and dipped into the pond
from buckets.
Other poisons used in fish ponds are quicklime, teaseed
cake, camelia
seed cake, tobacco waste, and powdered croton seed.
These are some
application rates:
Quicklime
: 160 kg/ha
Teaseed
Cake : 150 kg/ha
Camelia
Seed Cake : 50 to 200 kg/ha, depending
on depth
Powdered
Croton
Seed
: 50 to 200 kg/ha,
depending on depth
Tobacco
Waste : 150 to 200 kg/ha
Most of these natural poisons will degrade (break down) and
disappear
from the water in 7 to 12 days.
After this period, seine the pond
again. If no live
fish are caught, stock the pond.
There are many chemicals which can be used to poison
predators in fish
ponds. However, many
of them stay in the ground too long.
Others are
dangerous. One of
the chemicals which can be used safely is saponin,
which is a component of teaseed cake.
Apply a dose of 0.5 ppm in the
pond.
In most places, there are fishermen and farmers who know of
some local
plant which causes fish to die.
For example, in India large ponds
that cannot be drained are poisoned with Mahuca oil cake
(Mahuca
latifolia, syn. Bassia latifolia), applied at a rate of 150
to 250 ppm
(1500 to 2500 kg/ha per meter of water depth).
This plant poison
breaks down in 10 to 20 days.
These types of poison are all better
sources of poison than are chemicals.
Many times, when there is a
tree that overhangs a pond, fish will be killed when the
tree leaves
drop into the pond.
Watch for plants which do this, and use them in ponds
instead of poisons in a chemical form.
DO NOT USE CHEMICALS LIKE ENDRIN, DIELDRIN, AND DDT IN
PONDS: THEY CAN
LAST IN THE GROUND FOR YEARS, AND LATER, KILL ALL THE POND
FISH. NEVER
USE POISONS WITHOUT FIRST CHECKING WHETHER THEY CAN BE USED
IN PONDS.
SOME POISONS KILL OTHER ANIMALS AND HUMAN BEINGS, AS WELL AS
FISH.
SUMMARY: FISH DISEASES &
TREATMENTS
TREATMENT
DISEASE
DISEASE ORGANISM IN
PONDS IN BATHS
Gill Rot
Branchiomyces sanguinis
Quicklime
Copper Sulfate
Saprolegnia
Saprolegnia
Quicklime
Copper Sulfate
Furunculosis
Slaked lime in
Drained Pond
Infectious Dropsy
Pseudomonas punctata
Burn or Bury Dead Fish
Columnaris
Chondrococcus columnaris
Copper Sulfate 1ppm
Copper Sulfate 500ppm
Cytophaga columnaris
for 2 minutes
Malachite Green 67ppm
for 10-30 seconds
Ich
Ichthyophthirius multifilis
Formalin 15ppm
Formalin 200-250ppm
Malachite Green 0.5ppm
Malachite Green 1.25ppm
Methylene Blue 2ppm
Salt 7000ppm
Acriflavin 10ppm
Costiasis and
Costia and Trichodina
Potassium Permanganate Salt
5-10% for 5-10
Trichodiniasis
3ppm
minutes daily
Anchor Worm
Lernea
Castor Oil
Formalin
Fish Louse
Argulus
Salt 3-5%
Formalin 250ppm for 1 hour
Nematodes
Dactylogyrus and Gyrodactylus Formalin 5ppm
Formalin 25ppm
10 Other
Methods of Fish Culture
Fish culture in ponds is the primary method of freshwater
fish culture.
However, there are other methods of fish culture used in
places where
ponds are not possible.
Fish Culture in Dams and Reservoirs
Water contained by dams and reservoirs is sometimes used for
fish culture.
These waters can be stocked with fry or fingerlings; the
adults are later
harvested with nets.
Raising fish in these waters is more difficult
than in ponds because these waters cannot be drained, and
the predators
cannot be removed.
Also, it is not possible to feed, fertilize, or
poison the water, so natural nutrients must provide enough
fish food.
But if there is no other water source available, culture in
dams and
reservoirs can work.
Culturing fish in
waters held by dams
and reservoirs can
be done more easily
if the fish are placed
in fish cages and
pens. These
structures
confine the fish to a
certain place and give
more control over the
fish.
<FIGURE>
12p175.gif (437x437)
In Cages
In many parts of the world, the only water available is
flowing water
or large bodies of water where it is not possible to divert
the water
into a pond. In
these waters, it is possible to grow fish in small
cages. Cage culture
can also be practiced in areas like swamps where
there is water not being used for any other purpose.
Cages can be rectangular boxes, bamboo cylinders, or
anything that
can be floated in a water current so that the water passes
through.
<FIGURE>
12p176a.gif (437x437)
In addition to bamboo, cages can be made out of such
materials as wire
screen, nylon mesh, and wood.
All cages must be anchored so that they
do not float away.
Cage culture is used in some countries in very fertile
waters (polluted
from sewage) with very good results.
Fish in cages usually get their
food from the water as it floats past the stationary cage,
but in some
cases, the caged fish are fed pellets of food daily.
<FIGURE>
12p176b.gif (534x534)
Fast flowing water is best for cage culture.
If the water is not flowing
very fast, problems such as oxygen lack and competition for
food can
occur. These can be
big problems in cages because there are usually more
fish placed in the small area of the cage than would
normally be in the
same area in the pond.
Cage culture is still experimental, but in ideal conditions,
good growth
rates have been shown by fish that were grown in cages and
given extra food.
<FIGURE>
12p177.gif (540x540)
Cages also are used inside ponds
for holding fish between harvest
and the time they are sold.
And, sometimes, cages are used
as breeding tanks -- like hapas.
Cages are also used to carry
fish caught in rivers to market,
strapped alongside a boat.
In Pens
Fish can also be cultured in pens inside lakes or offshore
areas. Fish
culture in pens has been done in Israel and Scotland for
years, and is
now being done in some Asian countries.
Pens are constructed of bamboo
or wooden poles that are forced down into the lake or shore
bottom.
Then nets are strung from pole to pole to form an
enclosure. The nets
are anchored into the lake bottom with weights or sinkers,
and the fish
are placed inside the pen for culture.
Fish grown in pens can be
controlled a little better than fish in cages because pens
are larger
(fish pens can be comparable in size to regular fish ponds)
and provide
more area and more food.
<FIGURE>
12p178a.gif (540x540)
Fish pens placed in fertile (productive) lakes have very
good growth
rates. In a fish pen
placed in a major lake in the Philippines, silver
carp stocked at 7 grams gained an average of 4 grams a day
in a 52-day
growing season.
Fish pens have many good points:
they require no extra feeding of fish,
no fertilization, and very little maintenance (although a
lot of care
is given to the nets).
The fish are stocked and harvested later at the
end of their growing season.
Fish pens can work in areas where the
water is not very productive, but in these areas, the fish
must be fed
supplementary foods.
Feeding rings are used so the food will stay in
the pen and not float out into the water.
Fish in pens are usually
harvested by gill nets; seines also may be used.
<FIGURE>
12p178b.gif (540x540)
There are some disadvantages to pens:
*
Pens are expensive to build.
The netting used must be nylon
or plastic so
it does not rot, and poles must be treated
so they do not
become waterlogged and rot. In the
Philippines,
it costs about
$1,428 (U.S.) to build a one hectare pen, using
nylon netting
and bamboo poles. This is comparable to
the
cost of a
one-hectare fish pond, but a pen can be destroyed
by a big storm
and a pond will no+ be destroyed.
*
A fish pen only lasts three to five years in
the water.
*
Fish pens are usually built in the shallow
areas of a
lake, where
they use space many fish need to feed and
spawn.
The pens, therefore, reduce the natural
production
in some lakes.
*
Fishermen must go further out into the water
to fish when
pens are in
the shallow areas.
Fish pens can also be built like fish cages so that they
float. Floating
fish pens are used most for marine fish research studies;
they also can
be used in lakes.
Floating fish pens can be as small as one hectare
in size, or as large as 10 hectares.
They are not destroyed by storms
as easily as pens anchored to the bottom, and they can-be
moved from
one site to another.
Fish pens may have an increasingly important role in future
fish culture
activities around the world.
In Rice Paddies
This manual has already mentioned the practice of culturing
fish in
fields with rice.
Here is further, brief mention of that subject.
<FIGURE>
12p179.gif (437x437)
The farmer digs deep trenches all along the dikes of the
paddy. He then
floods the field and plants the rice.
After the rice has grown to
a height of 5cm or so, fish can be placed into the paddy
field.
This culture method can be used only with fish that are
resistant to
low oxygen levels and are not herbivores - herbivores might
eat the young
rice plants. Clarias
catfishes are good fish to culture in rice
paddies because they ave accessory breathing organs which
help them to
breathe even when the paddy gets dry and the water in the
trenches gets
very low.
After the rice is harvested, the fish are caught in hand
nets and sold.
This is not really a culture of fish, but a culture of rice
with some
fish added. It can
be an easy way for a farmer who has no extra land on
which to build fish ponds to increase the total production
of his land.
Glossary
acclimate - to become adjusted to a change from the normal
environment
(also acclimatize).
acid - a substance that can dissolve in water and is sour or
bitter
in taste, and turns litmus paper from blue to red.
adhesive - a sticky substance; sticking or sticky to
something else.
aeration - adding oxygen to water by spraying or bubbling air
through
the water.
algae - small or large water plants from five classes of
plants.
alkalinity - the ability to combine with an acid to form a
salt.
aquaculture - the cultivation of animal and vegetable life
in water.
area - the length times the width of a piece of land or
other surface.
back washing - forcing water in the opposite direction from
its
normal flow.
barbels - sensitive organs that hang down on the sides of
the mouth
of certain fishes.
basic - having base forming elements (alkaline on reaction).
bloom - a very good growth of algae in a pond that has a
strong green
color.
bottom feeders - fish that feed on bottom organisms
(organisms that
live in mud on the pond bottom).
breeding - the cycle of reproduction in animals.
brine - water that is saturated with common salt, or the
water from
a salt water body (the ocean).
brood ponds - ponds where the fish used for breeding are
kept.
brood stock - the fish used for breeding in fish ponds.
cage - an enclosure to hold fish in the water.
captivity - the state of being held in a confined place
(fish in
ponds are captive).
carnivore - an organism that eats animal products.
centrifuge - the machine that uses centrifugal force to
separate
materials of different densities.
compete - to fight for something against someone or thing.
contaminant - something that makes something else impure; a
pollutant.
cooperative - an organization of people that are working
together for
a common purpose.
dam - the wall of a fish pond.
debris - rubbish, garbage, anything that is not supposed to
be in a
certain area (pond).
density - the number of fish in a pond.
dike - the wall of a fish pond.
diversion channel - a ditch that takes water from a stream
or river
to a fish pond.
elevation - the height of land.
exotic species - fish cultured in ponds that are not native
to the area.
fertility - being very productive.
fertilizer - anything added to water or soil to make it more
productive.
fingerling - a fish that is about as long as a man's finger
(6-10cm).
fishculture - the breeding and cultivation of fish in ponds.
fry - fish that have just hatched until they reach
fingerling size.
genitals - reproductive organs.
genital opening - the opening on the fishes' body where the
eggs or
sperm are released.
gills - the part of a fish that allows it to breathe in the
water.
gravity - the tendency of things to fall downwards towards
the center
of the earth.
hapa - the mesh enclosure in ponds where fish can be
spawned.
herbivore - an organism that eats only plants and plant
products.
hypophysation - hormone injection to induce breeding of
fish.
hypophysis - the pituitary gland.
hormones - components that are secreted by glands of the
body to cause
certain changes in the body's functions.
impermeable - a substance that nothing can leak thru.
induced spawning - causing a fish to spawn by injecting it
with hormones.
introduced species - fish not native to an area that are
used in fish
ponds of the area.
kakaban - an egg collector.
mortality rate - the rate of death.
natural food - food that a fish eats in nature.
niche - what an organism does; its job in the community.
nutrient - an ingredient of food that is healthful.
omnivore - an organism (like man) that can eat both plants
and animals.
operculum - the gill covering.
oxygen - a gas that is necessary for all life.
pens - enclosures for fish culture on large bodies of water.
phytoplankton - tiny green or brown plants that are
microscopic,
free-floating in water, that are used as food by fish.
photosynthesis - the process on which green plants produce
food for
themselves and release oxygen into the water.
pituitary gland - the gland that releases hormones
controlling the
reproductive cycle in animals (like fish).
plankton - the tiny plants and animals that grow in ponds
that are
eaten by fish.
ponds - any enclosure that holds water so that fish can be
grown
inside it.
predators - animals that prey on other animals.
productivity - ability to grow food in a pond, whether it is
plankton
or fish.
reproduction - producing offspring.
respiration - breathing.
serrations - rough edges, like on a fishes' fin.
slope - the slant of land.
spawning - the release and fertilization of eggs and sperm.
stress - any change that is not normal in the environment
that creates
problems.
trash fish - fish not wanted in the pond, or fish that are
too small to
eat or spoiled fish.
watertight - impermeable.
zooplankton - small animals in ponds that can be seen with
the naked eye.
Resources
1.
American Public Health Association.
1971.
Standard methods
for examination
of water and wastewater. 13th ed. Am.
Pub.
Health Assoc.,
Washington, D.C. 874 p.
2.
Anderson, Steven E.
1973.
A manual of fish farming for tropical
Africa.
University of Minnesota, St. Paul, Minn. 46
p.
(xeroxed copy)
3.
Avault, James W., Jr., 1965.
Preliminary studies with grass carp
for aquatic weed
control. The Progressive Fish
Culturist.
27 (4):
207-209.
4.
Avault, James W., Jr. and E.W. Shell.
1966.
Preliminary
studies with the
hybrid tilapia Tilapia nilotica X Tilapia
mossambica.
FAO World Symposium on Warm Water Pond Fish
Culture.
Rome, Italy.
5.
Avault, James W., Jr., R.O. Smitherman, and
E.W. Shell. 1966.
Evaluation of
eight species of fish for aquatic weed control.
FAO World
Symposium on Warm Water Pond Fish Culture.
Rome, Italy.
6.
Aylward, Francis and Mogens Jul. 1975.
Protein and nutrition
policy in
low-income countries. Charles Knight
and Company,
Ltd., London.
150p.
7.
Bardach, John E., John H. Ryther, and
William O. McLarney. 1972.
Aquaculture. John Wiley &
Sons, Inc., New York. 868 p.
8.
Beckert, Heino.
1967. Culture of some
common fish parasites for
experimental
studies. Zoology-Entomology Dept.
Series, Fisheries
5.
Agricultural Experiment Station, Auburn
University, Auburn,
Alabama.
28 p.
9.
Best, Cody D. 1975.
Personal communication.
10. Bharadwaj, R.
S., Stephen Crawford, and Lauren C. Watson.
1973
Manual for fish
culture in Rajasthan and Madhya Pradesh.
American Peace
Corps. New Delhi, India.
66 p.
11. Boyd, Claude E.
1971. Phosphorus dynamics in
ponds. Proceedings
25th Ann. Conf.
Southeastern Assoc. Game and Fish Commissioners:
418-426.
12. Boyd, Claude E.,
E. E. Prather, and Ronald W. Parks.
1975.
Sudden morality
of a massive phytoplankton bloom. Weed
Science.
23 (1):
61-67.
13. Clemens, Howard
P. and Kermit E. Sneed. 1962.
Bioassay and use
of pituitary
materials to spawn warm-water fishes.
Research
Report 61,
Bureau of Sport Fisheries and Wildlife, United States
Department of
Agriculture (USDA). 30 p.
14. Crane, John S.,
et al. 1966.
Togo fish project manual.
United
States Peace
Corps. Oklahoma University, Norman,
Olkahoma.
158 p.
15. Delmendo, Medina
N. and Robert H. Gedney. 1974.
Fish
farming in pens
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Laguna Lake
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MEASUREMENTS USED IN THIS MANUAL
1 gram (gm)
= 1000 milligrams (mg)
1 kilogram (kg)
=
1000 gm = 2.2 pounds (lb)
1 mg/l
= 1 part per million (ppm)
1 liter (l)
= 1000 milliliters (ml) =
0.26 gallons (gals)
1 inch (in)
= 2.54 centimeters (cm)
1 foot (ft)
= 30.5 cm
1 meter (m)
= 100 cm = 1000 millimeters
(mm) = 39,37 inches
1 are
= 100 square meters
([m.sup.2])
1 hectare (ha)
= 10,000 [m.sup.2] = 100 ares
= 2.5 acres
[degrees] Centigrade (C)
= 5/9 x ([degrees] F - 32)
[degrees] Fahrenheit (F)
= (9/5 x [degrees] C) + 32
INDEX
Acclimate - p. 49
Acids - p. 15, 17, 90
Alkalinity - p. 89 - 90
Anal fin - p. 34
Anal vent - p. 34
Anchor worm - p. 168 - 169
Anguilla japonica - p. 39, 50
Anus - p. 35
Application rates - p. 97 - 100
Argulus - p. 169
Aristichthys nobilis - p. 39, 43
Aquaculture - p. 1
Bacterial diseases - p. 166
Barbels - p. 35
Barbus gonionotus - p. 39, 47
Barrage ponds - p. 19 - 21
Black carp - p. 40, 44
Bighead carp - p. 2, 29, 39, 43
Blooms - p. 93
Bothriocephalus gowkongensis - p. 170
Bottom-water overflow - p. 62 - 63
Breeding - p. 19 (see "Spawning")
Brood stock - p. 128 - 130
Buffering ability - p. 90
Cage culture - p. 176 - 177
Calcium - p. 90
Carassius auratus - p. 39, 50
Carassius carassius - p. 39, 50
Carbohydrates - p. 3 - 4
Carbon dioxide - p. 83 - 87
Carp - p. 2
Chinese - p. 2, 43
- 45, 109, 119, 135, 146 - 147
Common - p. 2, 37,
40 - 42, 108 - 109, 118, 130 - 132, 148
Indian - p. 45 -
46, 109, 119, 136, 148
Carpenter's level - p. 56
Catch basin - p. 39, 45
Catla - p. 39, 45
Catla catla - p. 39, 45
Caudal fin - p. 33
Caudal peduncle - p. 33
Centrifuge - p. 143 - 145
Chanos chanos - p. 39, 49
Characteristics of fish - p. 33
Cirrhina molitorella - p. 39, 44
Cirrhina mrigala - p. 39, 46
Clarias batrachus - p. 39, 47, 138
Clarias catfish - p. 29, 39, 47, 138, 147
Clarias macrocephalus - p. 39, 47, 138, 147
Clay soil - p. 15 - 16
Columnaris - p. 167
Compost - p. 96 - 97
Construction - p. 53 - 78
Cooperatives - p. 8
Costia - p. 168
Crucian carp - p. 39, 50
Crustacean parasites - p. 168
Ctenopharyngodon idellus - p. 39, 44
Culture in pens - p. 177
Cyprinus carpio - p. 40 (see "common carp")
Dactylogyrus - p. 169
Dams - p. 19, 54
Depth of ponds - p. 25
Dikes - p. 54
Diseases - p. 165
Diversion ponds - p. 21 - 23
Dorsal fin - p. 33
Double-sleeve overflow - p. 63
Drainage ditches - p. 20, 69
Drainage systems - p. 55, 60 - 69
Eggs - p. 36
Eels - p. 39, 50, 140
Elbow joint - p. 62
Elements - p. 4
Exotic species - p. 38
Fats - p. 3 - 4
Feeding - p. 116 - 117
Feeding ring - p. 117
Fertility - p. 16 - 17
Fertilizers - p. 93, 120
Inorganic - p. 99 -
100
Organic - p. 95 -
96
Filters - p. 14, 70 - 73, 116
Fingerlings - p. 19, 37, 113, 123 - 128
Fish culture - p. 1
Fish louse - p. 169
Fish farming - p. 6
Fish meal - p. 163
Food - p. 7, 100 - 106
Natural - p. 101
Supplementary - p.
101, 117 - 119
Food quotient - p. 101 - 102
Fry - p. 19, 36, 110 - 113, 123 - 128
Fungal diseases - p. 165
Furunculosis - p. 166
Genital opening - p. 34
Genital papilla - p. 35
Gill net - p. 149
Gill rakers - p. 34
Gills - p. 34
Gley - p. 77
Goldfish - p. 39, 50
Gourami - p. 40, 46, 47, 137
Kissing - p. 40,
49, 138
Snakeskin - p. 40,
49, 138
Three-spot - p.
40, 49, 138
Gravity - p. 17
Gyrodactylus - p. 169
Hapa - p. 136 - 137
Hard water - p. 90
Hardness - p. 89 - 90
Harvesting - p. 149 - 156
Helostoma temmincki - p. 40, 49
Heterotis niloticus - p. 40, 48, 139
Hormone injection - p. 141
Hybrid vigor - p. 38
Hydrilla
verticillata - p. 49, 84, 138
Hypophysis - P. 142
Hypothalmichthys molitrix - p. 40, 43
Ichthyophthirius multifilis - p. 167 - 168
Inlet, water - p. 20 - 21, 55, 69 - 70
Inorganic fertilizers - p. 99 - 100
Induced spawning - p. 141 - 148
Kakaban - p. 132
Key - p. 75 - 76
Kissing gourami - p. 40, 49, 138
Labeo rohita - p. 40
-45
Lateral line - p. 34
Lernea - p. 168 - 169
Levee - p. 54
Level - p. 56
Lime - p. 79 - 80
Limestone - p. 80
Litmus paper - p. 89
Magnesium - p. 90
Management - p. 107 - 148
Daily - p. 115
Monthly - p. 121
Marketing - P. 152 - 153
Milkfish - p. 39, 49, 50, 140
Monk - p. 65 - 69
Monoculture - p. 26 - 28
Monosex culture - p. 30 - 31
Mortality rate - p. 125
Mrigal - p. 39, 46
Mud carp - p. 40, 44
Mugil cephalus - p. 40, 51
Mullet - p. 40, 51, 140
Mylopharyngodon piceus - p. 40, 44
Nets - p. 149
Nutrients - p. 3, 16 - 17, 92 - 93
Number of ponds - p. 23
Operculum - p. 34
Organic fertilizers - p. 95 - 96
Optimum temperatures - p. 81
Osphronemus goramy - p. 40, 46 - 47
Overflow channels - p. 20 - 21
Oxidation - p. 85
Oxygen - p. 14, 19, 83 - 88
Paddy culture - p. 179
Parallel ponds - p. 22 - 23
Pectoral fins - p. 33
Pelvic fins - p. 33
Pen culture - p. 177 - 179
pH - p. 89
Phosphates - p. 99 - 100
Photosynthesis - p. 84
Phytoplankton - p. 84
Pituitary gland - p. 142
Plankton - p. 25, 36, 83 - 84
Planning - p. 11 - 52
Polyculture - p. 28 - 30, 45, 108
Poison - p. 171
Pond bottom - p. 59
Pond preparation - p. 79
Pond site - p. 58
Predators - p. 19, 121, 171 - 172
Preservation - p. 157
Protein - p. 3 - 5
Protozoan diseases - p. 167
Pseudomonas punctata - p. 167
Puntius gonionotus - p. 47 (also P. javanicus)
Quicklime - p. 80
Respiration - p. 83
Rivaldi valve - p. 61 - 62
Rohu - p. 40, 45
Rosary ponds - p. 22
Run-off - p. 13
Salting - p. 157 - 162
Saprolegnia - p. 166
Sealing pond - p. 77 - 78
Secchi disc - p. 91
Seines - p. 150 - 151, 155 - 156
Serranochromis robustus - p. 166
Silt - p. 74
Siltation tank - p. 74
Silver carp - p. 2, 29, 40, 43
Siphon - p. 61
Site selection - p. 11 - 13
Size of ponds - p. 23 - 25
Slope - p. 17 - 18, 55 - 59, 77
Sluice - p. 20, 64 - 65
Smoking - p. 162
Snakeskin gourami - p. 40, 49, 138
Soft water - p. 15, 74
Soil - p. 15, 74
Spawning - p. 130
Induced - p. 130,
141 - 146
Natural - p. 130 -
140
Spoiled fish - p. 163
Springs - p. 13
Stocking - p. 107, 109 - 114
Density - p. 107
Rates - p. 108
Stripping - p. 145 - 146
Superaturation - p. 99 - 100
Surveying - p. 55
Tawes - p. 39, 47, 48, 139
Temperature - p. 81
Threespot gourami - p. 40, 49, 138
Tilapia - p. 2, 29 - 31, 40 - 43, 109, 119, 133 - 134
Tilapia macrochir - p. 40
Tilapia melanopleura - p. 40
Tilapia mossambica - p. 2. 40, 42
Tilapia nilotica - p. 2, 40, 42
Topography - p. 17
Trash fish - p. 163
Trichodina p. 168
Trichopterus pectoralis - p. 40, 49
Trichopterus trichopterus - p. 40, 49
Turbidity - p. 25, 90 - 92
Turn-down pipe - p. 62
Walls - p. 19, 54, 74
Water quality - p. 14
Water supply - p. 13
Worm parasites - p. 169
Wells - p. 14
Yolk sac - p. 36
Zooplankton - p. 84
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