Rice - Fish Culture in China (IDRC, 1995, 240 p.) Part I: Review and Outlook Rice-Fish Culture in China: The Past, Present, and Future Rice-Fish Culture in China: Present and Future Scientific and Technological Development of Rice-Fish Culture in China Development of Rice-Fish Farming in Guizhou Province Reforming Rice-Fish Culture Technology in the Wuling Mountains of Eastern Guizhou Province The Development of Rice-Fish Farming in Chongqing City Development of Rice-Fish Farming in Jiangsu Province Rice-Fish Culture and its Macrodevelopment in Ecological Agriculture Value of the Rice-Fish Production in High-Yielding Areas of Yuyao City, Zhejiang Province A Comparative Study of the Ability of Fish to Catch Mosquito Larva

Rice - Fish Culture in China (IDRC, 1995, 240 p.)

Part I: Review and Outlook

Rice-Fish Culture in China: The Past, Present, and Future

Cai Renkui, Ni Dashu, and Wang Jianguo

The combination of rice and fish has a long history in China. The practice of rice-fish farming may have evolved from pond culture. The canon for fish culture written by Fan Li about 400 BC states:

Dig six mu of land into a pond...

put 2000 fry into the pond...

sell the rest in the market.

In a good year with ample rainfall and moderate weather, 2000 carp fry could produce numerous eggs. Some wise farmers may have placed excess fry in their ricefields. The fish in the ricefields may have grown better than those in the ponds, and the practice of raising fish in ricefields was born. There are no records of when the practice started, but this seems to be a logical explanation of how rice-fish farming began in China.

The archeological and written records do suggests the rice-fish culture is almost 2000 years old. In 1964-65, tombs of the mid-Eastern Han Dynasty (25-220 AD) were excavated in the suburbs of Hanzhong County, Shanxi Province. Two clay models were unearthed: a model of a pond and a model of a ricefield. The pond model contained 15 miniature pieces (6 common carp, 1 soft-shell turtle, 3 frogs, and 5 water chestnuts). In 1977, a stone carving of a pond and ricefield model was discovered in the brick tomb of the Eastern Han Dynasty in Emei County, Sichuan Province. Half the stone was carved into a pond with frogs, fish, and ducks. The other half was carved into a ricefield with an inlet and outlet, two farmers toiling on one side, and two heaps of manure on the other. In 1978, four mid-Han Dynasty tombs with 200 relics were excavated in Mian County, Shanxi Province. One of the intact relics was a ricefield model containing 18 pottery miniatures of aquatic plants and animals. In it were sculptured frogs, eels, spiral shells, crucian carp, grass carp, common carp, and turtles. Another of a winter ricefield showed farmland with a reservoir that also contained these fish.

These relics suggest that at least 1700 years ago, rice-fish culture was practiced in the vicinity of Hanzhong and Mian Counties in Shanxi Province, and in Emei County in Sichuan Province. The fish species stocked in the ricefields were common carp (Cyprinus carpio), crucian carp (Carassius auratus), grass carp (Ctenopharyngodon idellus), and silver carp (Hypophthalmichthys molitrix). The bamboo fish trap and sluice gate that were installed at the inlet and outlet indicate that a primitive model of rice-fish culture existed at that time.

The earliest written record of rice-fish culture is from Recipes for Four Seasons, which was written in the Wei Dynasty (220-265 AD):

A small fish with yellow scales and a red tail, grown in the ricefields of Pi County northeast of Chendu, Sichuan Province can be used for making sauce.

The small fish with yellow scales and a red tail could be common carp. This indicates that common carp may have been grown in ricefields in Pi County. This record coincides with excavated relics. An alternative view is that the fish referred to is a type of small carp that “came from rice paddies” but was not necessarily raised in the ricefields. It is possible that, instead of being raised by rice growers, the fish was washed into ricefields during the rainy season through flooded waterways.

Rice-fish culture probably continued to develop. The next written record is found during the latter part of the Tang Dynasty. Liu Xun (about 889-904 AD), wrote in Wonders in Southern China:

In Xin, Long, and other prefectures, land on the hillside is wasted but the flat areas near the houses are hoed into fields. When spring rains come, water collects in the fields around the houses. Grass carp fingerlings are then released into the flooded fields. One or two years later, when the fish are grown, the grass roots in the plots are all eaten. This method not only fertilizes the fields, but produces fish as well. Then, rice can be planted without weeds. This is the best way to farm.

The districts of Xin and Long are now in the vicinity of Xinxing and Luoding Counties in Guangdong Province. This means that rotational rice-fish farming was practiced there over 1000 years ago. The chronicle of Shunde County, Guangdong, from the Ming Dynasty (about 1573) states that:

The periphery of a land was trenched as a plot, called the field base.... In the plot, a pond was dug to rear fish. During the dry season, rice seedlings were transplanted to the plot. The area might be several hectares.

According to this chronicle, the area for rice-fish culture was expanded in Guangdong 400 years ago.

Formal research appears to have started in the 20th century. In 1935, a rice-fish culture experiment was conducted in Songjian, Jiangsu Province. The species stocked were black carp (Mylopharyngodon piceus), grass carp, silver carp, bighead carp (Aristichthys nobilis), and common carp. During the rice-growing period, the weight of the silver carp increased 50-fold and the weight of common carp increased 20-fold. After 2 years, 20 000 fry hatched and were distributed to farmers for culture in rice paddies. Scientists provided technical assistance.

After the founding of the People’s Republic of China in 1949, rice-fish culture developed quickly. In 1954, the fourth National Aquaculture Meeting proposed the development of rice-fish culture across the country. By 1959, the area of rice-fish culture had been expanded to 666 000 ha.

From early 1960s to the mid1970s, several factors, including the intensification of rice production and the large-scale application of chemical insecticides, impeded the development of rice-fish culture. For example, in Guangdong Province the area of rice-fish culture dropped from 33 333 ha in the early 1950s to 320 ha in the mid-1970s, and in Hunan Province the area dropped from 232 000 ha in 1958 to 5333 ha in 1978. (The years 1965-75 also coincided with the cultural revolution. During this period, the raising of fish was considered a bourgeois way of making money and was officially discouraged. In addition, there were severe dislocations of research and extension services during this time.)

Rice-Fish Farming in China Today

During the late 1970s, there were changes in rice production. Improved modern varieties of rice and less toxic chemicals were used and there were changes in the units of production. The production-contract system was implemented in rural areas starting in 1978 and this allowed individual families to become the main units of production. In addition, there was a rapid development of aquaculture, which required the production of a large amount of fry and fingerlings. This demand was partly met by fingerling production in ricefields. Research and supporting policy and development activities have also encouraged the expansion of rice-fish production.

The research established an optimum ecological system to increase rice production, economize labour, and maximize economic returns. This lead to the evolution of a theory of rice-fish mutualism that has provided the theoretical basis for rice-fish culture. The practice has now spread to all rice-growing areas in China through the adaptation of rice-fish techniques that are suitable to local agroecological conditions.

A number of regional and national meetings focused attention on rice-fish culture and advanced its development. In 1983, a workshop on Fish Farming for Eradicating Mosquitoes was held in Xinxiang, Henan Province, to exchange information on eradicating mosquitoes by rearing fish in ricefields. The First National Ricefield Fish Culture Seminar was held on 11-15 August 1983 at Wenjian County, Sichuan Province, under the auspices of the Ministry of Agriculture, Animal Husbandry and Fisheries (now the Ministry of Agriculture). The seminar established a large coordination group for Eastern China to popularize rice-fish farming techniques.

The potential and actual production in Eastern China is summarized in Table 1. There are 9 million ha of ricefields in Eastern China. This accounts for one-third of the country’s total rice area, and 45% of it is suitable for raising fish. Before 1982, rice-fish farming was concentrated in the mountainous areas of Jiangxi, Fujian, and Anhui and covered only 26 000 ha. The area was expanded to include the plains and, by 1986, 138 000 ha were in production and yielded an average of 183 kg of fish per hectare.

In 1983, a key research project on the economics of aquatic resources in China included a subproject on economic problems related to rice-fish culture. The scientists, who thoroughly studied the economic benefits of rice-fish culture, received the Second Science and Technology Progress Award from the Agriculture Ministry in 1988.

In 1984, the Ministry of Agriculture, Animal Husbandry and Fisheries (MAAHF), organized a project to popularize the technique of raising fish in ricefields in Sichuan, Beijing, Hebei, Shanghai, Jiangsu, Anhui, Zhejiang, Jiangxi, Fujian, Henan, Hubei, Hunan, Guangdong, Guangxi, Shaanxi, Guizhou, and Yunnan. To promote the project, a technical group of six researchers was formed to provide guidance. The members of the group were: Jiang Cimao of the Aquatic Products Bureau of Sichuan Province, Ni Dashu of the Institute of Hydrobiology of the China Academy of Sciences, Yin Pizhen of the Aquatic Products Institute of Jiangxi Province, Yang Yongshuan of the Aquatic Products Bureau of Hubei Province, Yang Jintong of the Aquatic Products Bureau of Hunan Province and Xu Xushi of the Bureau of Agriculture, Animal Husbandry and Fisheries of Zhongging City. The project sought to popularize the practice on a large scale. Initial achievements won the project a first-class award for technological progress from the MAAHF in 1986.

In 1985, 17 institutes were involved in another key research project called, “Ricefields as Fish Nurseries and Fish Grow-out Systems.” This project, under the auspices of the National Aquatic Products Bureau, aimed to rear hybrids of common carp, tilapia, and crucian carp (Carassius carassius) in ricefields and to nurture grass carp fingerlings in ricefields. Each province was requested to extend rice-fish culture in a 200 ha demonstration area. The target yield was 225-625 kg of fish per hectare. The total demonstration area of rice-fish culture in the eight provinces south of the Yangtze River was 1600 ha. The project sought to promote the extension of rice-fish culture in the country to cover a total area of 800 000 ha.

There was also an increase in rice-fish culture in Northern China. In 1985, the Aquatic Products Section of the Water Resources Committee of the city of Urumqi in the Xinjiang Uygur Autonomous region in Northwest China, carried out an experiment on rearing fish varieties in ricefields in the northern suburbs of Urumqi. They put 1977 fingerlings in two batches (10 and 2-3 cm in length) into a 0.4-ha experimental field. After 68 and 87 days, they harvested 174 kg of fish per hectare. The largest fish weighed 0.25 kg and the average weight was 0.11 kg. Rice output was 9292.5 kg/ha, 18% more than in 1983. Net profit was CNY 1916/ha.

From 1984 to 1985, the Rice Institute of the Agricultural Reclamation Academy in Heilongjiang Province, Northeast China, conducted experiments on rice-fish farming in high, cold areas. Rice yields increased by 7.2-12.1%, and the survival rate of fingerlings to harvest was 71.3-88.9%. The net value of the output increased by CNY 656-950/ha. Grass carp averaged 0.2 kg in weight; common carp averaged 0.15 kg. Meanwhile, in Huanren County, Liaoning Province, another rice-fish culture experiment stocked grass carp and common carp as major species and tilapia as minor species in a 0.1-ha ricefield. They harvested 85.8 kg of fish and rice yields increased by 7.3-8.4%.

In 1985, Changchun City in Northeast China’s Jilin Province raised common carp fry during the summer in 4.3 ha of ricefields. They harvested 35 000 fingerlings that measured 10-15 cm in length and weighed a total of 875.5 kg. The ricefields yielded 279 kg of fish per hectare. The current situation (1986) of rice-fish production in China is summarized in Table 2. There are almost 1 million ha of rice-fish culture in China in 15 provinces and three municipalities (Beijing, Shanghai, and Zhongging). In addition, experimental culture is being carried out in the northern provinces of Jilin, Liaoning, and Heilongjiang and in the Xinjiang Uygur Autonomous Region. Rice-fish culture is now practiced from southern Guangdong and Guangxi at 22°N to Beijing at 40°N, and experimental activities as far north as Heilongjiang Province (45°N).

The Development of Rice-Fish Culture Techniques

Concept and Significance of Rice-Fish Farming

The new concept of “mutualism” in raising fish in ricefields is entirely different from the traditional purpose and nature of rice-fish culture. The mutualism concept is to improve rice production by letting herbivorous fish eliminate weeds that compete with rice plants for sunshine, fertilizer, and space. At the same time, fish in ricefields feed on weeds, plankton, and benthos, and form an optimum ecological system that benefits both the fish and the rice. Traditionally, the idea was simply to raise fish with rice as an additional source of food. Now the concept includes the mutualism of both crops and has indeed become an effective way to boost rice yields. There are two basic forms of rice-fish farming: (1) rotating rice and fish, and (2) growing fish and rice together. Rice-fish rotation involves growing rice one season and raising fish the next. This method has been extensively adopted in winter ricefields, in fields that need to conserve water, and in low-lying areas in Sichuan Province. The fish raised in these fields are mainly adult or large fish.

The new concept of rice-fish farming combines the otherwise contradictory principles of growing rice and farming fish. By making full use of the mutual benefits of both rice and fish, the new concept provides a modern biological technique to invigorate agriculture in China. The emphasis is on growing rice and the role of the fish is to enhance the growth of the rice plants. But, the ultimate goal is to increase the production of both rice and fish in rice-growing areas. There are many advantages of growing fish with rice:

· The fish increase rice yields by more than 10%;

· A 0.07-ha ricefield can yield 300 fingerlings each measuring 10-16.5 cm. When table fish are reared, 150-450 kg/ha can be harvested. In rice-fish rotation, more than 50 kg of fish can be caught from 0.07 ha of surface water;

· The fish feed on weeds and worms, and loosening up the soil. This helps reduce labour requirements and is one of the outstanding benefits of raising fish in ricefields;

· The fish (especially grass carp) conserve and enrich the fertility of the water and soil and therefore stimulate the growth of rice plants and increase grain yields;

· The fish eliminate some insect and disease pests of rice, and in addition eat mosquito larvae, which are pests to both animals and people, and thus help to reduce the incidence of meningitis, malaria, and filariasis.

Rice-fish farming is closely integrated with freshwater fish farming in China, especially in ponds, reservoirs, lakes, and family ponds. Freshwater aquaculture requires increased quantities of fry. The demand for fry cannot be met by relying on stock fish farms or by expanding stock fishponds.

The use of ricefields to grow fingerlings has allowed the demand to be met. If the area for rice-fish farming in China was expanded by 6.7 million ha, rice production would increase by more than 2 million tonnes and 30-50 billion fingerlings would be produced. This would also help increase the annual harvest of freshwater fish.

Fish Species Stocked in Ricefields

In ancient times, the fish species stocked in ricefields were: common carp, crucian carp, grass carp, silver carp and bighead carp. In the 1950s, the species used were: black carp (Mylopharyngodon piceus), Chinese bream (Megalobrama amblycephala), tilapia (Oreochromis mossambicus and O. niloticus), mud carp (Cirrhina molitorella) in the south, loach (Misgurnus anguillicaudatus and Xenocypris argentea) in Guangxi and Hunan, and snakehead (Ophiocephalus argus) in Guangdong.

In the 1960s and 1970s, rainbow trout (Salmo gairdneri) were introduced in the north, and catfish (Clarius leather) in the south. In the 1980s, the new species used were: carp (Carassius auratus), aquatic crab (Eriocheir sinensis); shrimp (Macrobrachium nipponensis), American snail, pearly clam, and field snail.

Increased Rice Yields After Fish Culture

There is considerable evidence that fish increase the yield of rice. Table 3 summarizes the information from a number of experiments throughout China. All experiments show an increase in rice yield of 2-34% (average of 11.8%).

Chemical Insecticides Applied to Ricefields

There are over 50 pests and 10 diseases that attack rice. The major pests are: yellow stemborer (Tryporyza incertulas and Chilo simplex), green rice leafhopper (Nephatettix apicalis), rice plant skipper (Parana guttatus), and rice blast (Piricularia oryzae), which is the most serious disease. Secondary pests and diseases are: snout beetle (Echinocnemus squameus), rice leafroller (Cnapholocrosis medinalis), yellow-legged lema (Lama flavipes), locust (Oxya chinensis), and brown spot (Cochliobolus miyabeanus).

In the early 1970s, chemical insecticides toxic to fish gained widespread use. Some of these were 666, DDT, and limestone powder. Later, less toxic chemicals (Roxin, Dipterex, Kitazine, and Fenitrothion) were produced. Methods of application were improved to minimize damage to fish and to achieve the maximum effect of the chemicals. For example, the water level in the ricefields was increased before the chemicals were applied. Powdered chemicals were applied when the plants were covered in dew, and spray chemicals were applied when there was no dew. In some areas, fish were driven to trenches or sumps before the chemicals were applied. Insecticides were also applied in instalments or in patches. Table 4 shows the current dosages of chemicals that are used.

Development of Rice-Fish Culture

Ricefields can be used as fish nurseries or to produce fish for food. In fingerling production, either 450 000-600 000 eggs/ha or 300 000 fry/ha of common carp are stocked early in the season. By the summer, the fingerlings are ready for harvest. To nurture large-sized fingerlings, the stocking density should be 15 000-22 500/ha. If grass carp is the dominant species, 12 000-15 000 grass carp should be stocked per hectare with 3000-4500 silver carp and bighead carp and 4500-6000 common carp and bream.

In Shanxi Province, rainbow trout was cultured in winter fallows by using slightly running waters. Fish production was very high (30 t/ha). Rice-fish culture has been practiced, not only in shallow-water ricefields, but also in deepwater rice fields and in fields of wild rice (Zizania spp). In brackishwater along coastal reclamation areas, a rotational system is used. One crop of rice is grown one year, mullet (Mugil so-iuy) is cultured the next.

During the 1980s, several new developments occurred:

· Ridge rice planting - ditch fish farming system. This system is suitable for water-logged ricefields. The system involves a series of ridges and ditch in the ricefield. The rice is grown on top of the ridges and the fish in the ditch. The width of the ridge and the ditch is 40 cm, the height of the ridge is 80 cm, and water depth is 50 cm. (The dimensions of the ridge-ditch system appear to vary considerably. The ridge is often only 25 cm wide and 30 cm in height.)

· Rice-azolla-fish system. Rice is planted in the fields, azolla is cultured on the surface of the water, fish are cultured in the water, and squash or legumes are planted on the bunds. This is a multilevel comprehensive system of resource use.

· Running water system of trench fish farming. One or two broad trenches (1-1.5 m in width and 60-90 cm in depth) are dug in a ricefield. The trenches account for about 6% of the total area of the ricefield, and fish are cultured in the water running through the trenches.

Prospects for Rice-Fish Farming in China

China has 25 million ha of ricefields, and over 90% of this area is south of the Huai He River Basin. Although the practice has achieved excellent results in terms of scale and economic return, its potential to meet the needs of modern development remains untapped. If 10% of the ricefields south of the Huai He River were used (half for commercial fish and half for stocking fish), the commercial fish yields could be 346 000 tonnes (assuming 300 kg/ha) and the number of full-size fingerlings would be 5 billion (assuming 4500/ha). The area north of the Huai He River is not as suitable for rice-fish culture, but if 5% of the rice fields become rice-fish systems, they would produce 8000 tonnes of commercial fish and 243 million fingerlings. The total increase in rice output would be one million tonnes annually on the basis of the 1981 output (if annual increase is calculated at 10%) and commercial fish yields would reach 354 000 tonnes and 5.7 billion fingerlings. The number of fingerlings raised in ricefields would be sufficient to stock 0.75 million ha of water (e.g., ponds and reservoirs). The achievement of these goals would have very large ecological and economic benefits.

If fish farms were used to raise fry, ricefields were to be used to raise full-sized species, and ponds, reservoirs, and lakes were used to raise adult fish, fish farming would undergo considerable change. Fujian Province reported that, if ricefields are used to rear fingerlings, 200 ha of stock fishponds would be freed for intensive farming of commercial fish, and labour and feed, which would otherwise be used for breeding fingerlings, could be used for commercial fish farming. Jiangsu Province reported that, in 1986, Jianhu County used 4700 ha of ricefields to raise fish. Three major stock fish farms supplied enough fry to meet the need for big-sized stock fish for 2000 ha of intensive fish farming in the county. This indicates that the output of freshwater fish could be increased considerably.

Rice-fish farming has the potential to fully maximize the use of ricefields. Present trends for popularizing the practice are encouraging, and the area used to grow rice with fish is increasing yearly. In the past, the development of China’s aquatic products has been slow, quality has been poor, and supply was often short. There have also been policy problems that remain unsolved. As the internal structures of agriculture are adjusted, various localities are becoming aware that rice-fish farming is an effective way to increase rice production and improve economic, social, and ecological conditions.

Since the national conference on rice-fish farming in 1983, various provinces, autonomous regions, and municipalities have undertaken measures to popularize the practice in line with local conditions. The Science Commission and Aquatic Products Department of Fujian Province organized several research projects. They achieved success by strengthening their leadership and by coordinating technical forces. East China’s coordinating group met once a year to summarize work experiences and coordinate actions. Representatives from various provinces visited advanced units to draw on their experiences and to increase the awareness of leaders from different areas about the significance of rice-fish farming. They held meetings to discuss the practice and conducted training courses to expand the area of ricefields for fish farming.

Rice-fish farming should be combined with intensive fish farming in ponds, reservoirs, lakes, and cages to ensure that more fingerlings can be raised in ricefields. Recently, a national symposium called for the rapid development of ecological agriculture to improve productivity. Ecological agriculture has received increased attention in recent years, and the structure for agricultural production has been improved significantly. Undue emphasis used to be placed on plant culture; however, attention has now shifted to the comprehensive development of farming, forestry, animal husbandry, and fisheries. Instead of focusing only on economic results, both economic and ecological benefits are now considered. In the past, single items of technology were emphasized. Today, due attention is given to the comprehensive application of technical packages.

Rice-fish mutualism offers a model of ecological agriculture. However, fish farming has not yet been closely integrated with crop cultivation and the division of labour has not been clear; therefore, development and popularization have been slow. The production of both rice and fish can be maximized if agricultural researchers pay more attention to rice-fish farming and help hasten its development. It is imperative to integrate fish farming with crop cultivation. If the area for rice-fish farming was increased to 6.7 million ha as the area devoted to rice is increased, the supply of freshwater fish could be quadrupled.

Rice-fish farming can play an increasingly important role in freshwater fish farming if the nation’s leaders give it due attention, if the technology is sound, and if the practice is carefully adapted to local conditions.

This paper is a combination of two papers: The History of Rice-Fish Culture in China by Cai Renkui of the Freshwater Fisheries Research Centre, Chinese Academy of Fisheries Science, Wuxi, Jiangsu Province, and The Past, Present, and Future of Rice-Fish Farming in China by Ni Dashu and Wang Jianguo of the Institute of Hydrobiology, Academia Sinica, Wuhan, Hubei Province.

Rice-Fish Culture in China: Present and Future

Chen Defu and Shui Maoxing

In China, fish are raised in ricefields in the southeast and southwest mountainous areas where there are few bodies of water for growing fish and fishing regions and towns are far away. Rice-fish culture is a traditional and popular way for the people to grow their own supply of fresh fish in the mountainous areas of: Qingtian and Yongjia in Zhejiang Province; Jiening, Taining, Saxian, and Yongan Shaowu in Fujian Province; Yulin, Guilin, and Jinzhou in Guangxi Province; the southern part of Guizhou Province; and Pingxian, Jian, and Yichun in Jiangxi Province.

In these areas, the farmers practice rice-fish culture to raise fish for their own consumption, although it requires extensive management and fish harvests are poor. Before 1949, there was no organized extension of the technology; therefore, rice-fish culture did not improve.

Present Situation

Extension of Rice-Fish Culture

Since the founding of the People’s Republic of China in 1949, the government has paid more attention to rice-fish culture. In 1954, the First National Conference on Aquatic Products formally called for the promotion of rice-fish culture. The area devoted to rice-fish culture increased rapidly and reached over 670 000 ha by the end of the 1950s. During the mid-1950s to the early 1960s, rice-fish culture developed rapidly in the mountainous areas of south and north Zhejiang and in the plains and hilly areas of Shaoxin, Jin Hua, and Hangzhou. However, this development suffered a major setback during the 1960s to the mid-1970s when planting systems were reformed and highly toxic pesticides were used. The area devoted to rice-fish culture decreased drastically, but began to increase slowly by the end of the 1970s as improved breeds of rice and less toxic, but effective, pesticides were introduced. In the 1980s, more farmers became interested in rice-fish culture as the government encouraged its adoption and introduced a family contract system in rural areas.

In 1983, the office of the Central Committee of Patriotic Hygiene in Xinxiang City, Henan Province, held a meeting about controlling mosquitoes in ricefields. They decided to promote and disseminate information about rice-fish culture and to advance its development.

The first national meeting on rice-fish culture was held by the Ministry of Agriculture, Husbandry and Fishery in Wenjiang County, Sichuan Province, in August 1983. Similar meetings followed in provinces, cities, and autonomous regions. Rice-fish culture in China began a new period of rapid development. The total area of rice-fish culture increased 65% between 1983 and 1984. In Zhejiang Province, the total area was 18 127 ha in 1984, a 36% increase from the 12 353 ha in 1983.

In 1984, the Bureau of Aquatic Products of the Ministry of Agriculture, Husbandry and Fishery organized and launched a project “Extending the Techniques for Fish-Raising in Ricefields” in 17 provinces, cities, and autonomous regions The total area for rice-fish culture in the country increased to 846 700 ha in 1985 and to 985 300 ha in 1986 and had a positive effects on the economy, society, and ecology. The project received the first grade award for advanced scientific technology from the Ministry of Agriculture, Husbandry and Fishery in 1986.

Rice-fish culture has now developed and been adopted in the southeast and southwest mountainous areas and the plains, and the northeast and northwest regions. It is practiced in the ricefields of Sichuan, Hunan, Guizhou, Chongqing, Guangxi, Jiangxi, Anhui, Fujian, Zhejiang, Jiangsu, Yunnan, Guangdong, Henang, Shaanxi, Hebei, Xingjiang, Liaoning, Helongjiang, Beijing, and Shanghai.

Research on Rice-Fish Culture

Since 1949, the main research areas in rice-fish culture have been:

· The relationship between rice and fish and ways to increase rice production using rice-fish culture;

· The different forms of the ricefield that can be used for rice-fish culture (plain, ditches, pits, wide ditches, and ridges);

· Suitable breeds of fish (i.e., grass carp, common carp, crucian carp, murrel, and mud loach). A few silver carp and bighead carp can be raised together with these fishes in ricefields with wide ditches. The raising of grass carp is the most effective way to clear up weeds and pests. Adult grass carp grow quickly in ricefields; therefore, fish yields and economic returns are increased. Techniques to prevent grass carps from injuring the rice plants must be used;

· Comprehensive techniques to improve harvests from rice-azolla-fish systems;

· Economic evaluations;

· Suitable pesticides, their safe dosage, and methods of use, and the residual effects of methamidophos, carbofuran, and insect-paste in the rice-azolla-fish system;

· The control of mosquitoes in ricefields using fish-raising, and the development of the rural economy;

· Comprehensive techniques to efficiently manage agriculture, animal husbandry, and fisheries;

· The rates of absorption, transfer, and application of N and P, and the use of azolla by fish; and

· Feasibility studies.

Types of Rice-Fish Culture

There are two ways to combine rice and fish:

· Rice and fish together. Planting rice while raising fish is the main method used. The method makes full use of time, space, energy, and resources of the ricefield and provides economic benefits. Its shortcoming is the rather high requirement for labour and management.

· Rice and fish in rotation. Planting rice and raising fish are carried on alternately; therefore, the contradictions between growing rice and raising fish are avoided. After the rice is harvested, fish are raised in deepwater fields, which can improve fish yields. The disadvantages are that the growing period for the fish is shortened, and that the mutually beneficial and efficient relationship of rice-fish culture is lost. In regions with two rice harvests, the rotation of rice and fish will reduce rice yields.

The main methods of the rice and fish rotation are:

· early rice - late fish;

· early fish - late rice;

· after the harvest of one rice crop, fish are raised in deep water;

· fish are raised in clean summer fields for 1.5-2 months after the harvest of early rice and before the late rice is transplanted;

· fish are raised for 120-130 days in clean winter deepwater fields after the annual harvest of late rice (the fish are caught the following year before the early rice is transplanted); and

· in the same ricefield, two harvests of fish are raised and two crops of rice are planted during the same year (i.e., early rice - raising fish in summer, and late rice - raising fish in winter). In Guangdong Province, summer fish are raised for 40-50 days, winter fish for 80-100 days.

Yields and Techniques

Fish yields in ricefields have been low. The average yield of fish per hectare from 1982 to 1987 was 70.5, 82.5, 100.5, 126, 141, and 133.5 kg, respectively. New techniques and high-yield demonstration plots all over the country have led to increased fish yields. However, average yields in large areas of the country are still low. Traditional techniques of rice-fish culture are still used in most parts of China.

The reasons for low yields of fish from ricefields are:

· Low water volume and little shelter. Traditionally, ricefields used to raise fish do not have ditches or pits. The low volume of water in these ricefields results in insufficient dissolved oxygen and few plankton, high water temperature in summer, and few places for the fish to hide from predators. The density of the fish, the rate of catching, and yields are limited.

· Inbreeding of fish and genetic degeneration. Carp are raised in most ricefields in China. For example, Tian carp are popular in south Zhejiang, West Hunan, and Sichuan, Gao Bei carp and Jin carp are popular in the mountainous area of Guizhou, “Hehua” carp are popular in northern Guangxi. These breeds of carp have mild characteristics and do not jump well; therefore, they cannot escape easily. They are suitable for raising in ricefields. However, because of prolonged inbreeding, the breed characters have degenerated and the fish grow slowly.

· Small fish breeds. The old regions of rice-fish culture use the traditional method in which small fish are raised and, in some regions, fingerlings are stocked directly into the field. This has led to slow growth of fish and low survival rates.

· Insufficient feed. Artificial feed is not used in the traditional method. However, there is insufficient natural feed in ricefields, especially in mountainous areas. The weeds decrease as the fish grow; therefore, the fish do not get a sufficient supply of weeds during the middle and late growing stages of the rice.

· Low density of fish. For breeding, 10 500-22 500 summer fingerlings are raised per hectare. For food, 1500-7500 summer fingerlings and 750-1200 spring fingerlings are raised per hectare.

· Late stocking, early harvest, and short growing periods. Fingerlings are usually stocked a week after the rice seedlings are transplanted and the fish are caught during the rice harvest. The period for the rice and fish to grow together is short - about 90 days in regions with one rice crop and 160-180 days in regions with two rice crops. In southern China, 240 days (Jiangsu) and 330 days (Guadong) are considered suitable.

· Once raising and once catching. The fish carrying capacity in ricefields changes during the growing period. Early in the season, the field has many weeds and the fish are small; therefore, the natural feed is sufficient. Later, when the fish are larger, there are fewer weeds. The resources in the field no longer match the density of the fish.

· Small-scale production. The farmers consider the fish a by-product; therefore, the area used to raise fish in ricefields is small and scattered.

The Rise of Modern Rice-Fish Culture

Traditional rice-fish culture is no longer suited to the country’s social development, and it hampers the extension of modern methods of rice-fish culture. In the 1980s, several reforms were made:

· The layout of the ricefields used to raise fish was improved. The traditional plan was changed to include ditches, wide ditches, pits, and ridges. The volume of water was increased to improve the environment for the fish.

· Several breeds of fish are now used instead of a single breed. Fish (e.g., grass carp, common carp, nile tilapia, silver carp, variegated carp, and crucian carp) were selected to suit local conditions.

· Fish size was increased. Fingerlings 10-cm or larger are now used instead of fingerlings 6-8 cm in length.

· Stocking density of the fish was increased. Depending on the fertility of the soil and feed supply, 4500-6000 adult fish from the previous year and 3000-4000 summer fingerlings are raised per hectare. The numbers can be increased if conditions are improved.

· Shifting from late stocking - early harvest to early stocking - late harvest. Because the ditch, pit (pool), and ridge systems have permanent fish pits, fish-raising can begin in the winter. Fish are now raised continuously after the harvest of late rice in deep-water ricefields. If crops are planted in winter for spring harvest, fish are caught 2 weeks before wheat or rapeseed are planted.

· Feed or the rice-azolla-fish method are used instead of not feeding the fish.

· One-time raising and one-time catching were changed to alternative catching and raising.

The new techniques have improved average yields to 750-3000 kg of fish per hectare while increasing rice production. The highest fish yield reached 5500 kg/ha in two-crop ricefields in Zhejiang. These new approaches have helped to modernize the traditional methods of rice-fish culture in China.

Prospects for Rice-Fish Culture

Potential

Because of the country’s large population and limited agricultural land, agriculture in China is moving toward intensification. Rice-fish culture is part of this intensification. It is an effective way to increase the productivity of ricefields by harvesting both rice and fish. It is the quickest method to increase the economic efficiency of the ricefield and to help farmers increase their income.

There are about 25 million ha of ricefields in China. If 30% were to be used to raise fish, about 7.5 million ha would be available for rice-fish culture. If 600 kg of rice and 375 kg of fish were harvested per hectare, this would increase the country’s production to 45 billion kg of rice and 28 billion kg of fish. Less than 1 million ha of land, or 3.9% of the total area of ricefields, are now devoted to rice-fish culture. Therefore, there is great potential to develop rice-fish culture.

The rapid development of township industries has improved the skills of farmers. The development of family farms has prepared favourable conditions for the large-scale management of rice-fish culture using advanced scientific techniques. A modern and effective rice-fish industry will alter traditional concepts about rice-fish culture and encourage more farmers to raise rice and fish together.

Factors Limiting Development

· Fish can only be raised in ricefields with sufficient water resources and good irrigation and drainage. Poor water resources, drought, serious leakage, and poor water-holding capacity of the soil make rice-fish culture difficult in north China; whereas, south China is rainy and flood-prone.

· Higher economic efficiency can be achieved in township industries and trade businesses than in areas that practice traditional methods of rice-fish culture.

· The family-contracted fields are scattered and on a small-scale. Advanced and scientific methods of rice-fish culture are difficult for farmers to adopt without further land consolidation.

· Support systems for rice-fish culture are inadequate. It is very difficult for farmers to obtain loans, new and improved fish breeds, feed, fertilizer, and pesticides. There are also few technicians available to instruct farmers. Therefore, the breed characters of some carps that are popular with farmers degenerate and as a result the fish grow slowly.

· For a long time, traditional techniques have hindered the development of rice-fish culture because they prevent farmers from accepting and grasping modern techniques. Farmers worry that fish pits and ditches will affect grain yield. These ideas hamper the extension of rice-fish culture.

Strategies for the Development of Rice-Fish Culture

Rice-fish culture must be given as much attention as the production of food grains, and should be seen as a way to develop grain production and to improve the economic conditions of farmers. Several tactics can be used to improve rice-fish culture:

· The efficiency of rice-fish culture, and the area devoted to rice-fish culture in traditional regions, should be increased through technical training and increased funding.

· Testing sites should be established in plain areas and modern techniques should be extended to farmers to increase yields of rice and fish, and to spark interest in rice-fish culture in these high-production rice areas.

· Rice-fish culture should be extended to large farm families who mainly grow rice. The technology could help improve their livelihood and become pioneers in the large-scale development and efficient management of rice-fish culture in the country.

· Agricultural and aquatic products units should be merged to coordinate research and improve extension of practical techniques for rice-fish culture. The basic theories of rice-fish culture and techniques for good harvests of both rice and fish must be studied.

Chen Defu and Shui Maoxing are with the Soil and Fertilizer Institute, Zhejiang Academy of Agricultural Sciences, Hangzhou, Zhejiang Province.

Scientific and Technological Development of Rice-Fish Culture in China

Zhang Rongquan

Rice-fish culture is an organic method that integrates rice production and aquaculture. It enhances the growth of both rice and fish, maximizes the use of field and water resources, and effectively increases harvests. Several scientific and technological developments have been made to rice-fish culture techniques in China.

Development of Rice-Fish Culture Techniques

Traditional Aquaculture Techniques in Ricefields

Historical records show that Chinese farmers started raising fish in ricefields more than 1700 years ago. But despite its long history, rice-fish culture did not progress for many years and its development was hindered by feudal relationships. Farmers raised fish in ricefields as a sideline, usually only to augment their own meals. Rice-fish culture is described in the Tang Dynasty treatise (about 889-904 AD) Wonders in Southern China by Liu Xun:

... after the spring rains, water collects in the fields lots around the houses. Grass carp fingerlings are then released into the flooded fields. One or two years later, when the fish are grown, the grass roots in the plots are all eaten up. This method not only fertilizes the fields, but produces fish as well. Then, rice can be planted without weeds.

During the Ming and Qing Dynasties, rice-fish culture gradually developed into an important sideline in the countryside. But, because of various restrictions, it did not grow into an organized technique. Operations were often scattered and little information was available; therefore, methods and yields varied considerably in different areas. Yields were low and the scale of production and the techniques did not progress.

Before the founding of the People’s Republic of China, the Ministry of Agriculture and Forestry of the Kuoming-Dang Government promoted the development of rice-fish culture by stocking fingerlings in ricefields of Sichuan. They also published and distributed a brochure entitled An Elementary Introduction to Rice-Fish Culture. In Shong Jiang District, the Jiangsu Province Rice Experiment Station conducted experiments on rice-fish culture and provided technical guidance to local farmers. These efforts promoted rice-fish culture locally, but restrictions limited its impact on the rest of the country.

During the early period of the People’s Republic of China, rice-fish culture flourished as agricultural production was restored. Experiences in rice-fish culture were exchanged quickly and more districts began to adopt the technique. By 1959, the total area devoted to rice-fish culture had increased to about 670 000 ha. At this stage, fish were raised on a small-scale with traditional tall rice varieties grown without pesticides on level land. A few farmers dug fish ditches, which took up only 1% of the field area. The species raised were restricted to grass carp and common carp. Usually, the fish were not fed and only weeds were available. Production, efficiency, and benefits were low. Although there were new developments, rice-fish culture remained very traditional.

In later years, the system of rice cultivation was reformed and large quantities of fertilizer and toxic pesticides were used. Rice-fish culture decreased. Since 1978 new techniques have been developed.

New Techniques

China is very large and the natural conditions vary substantially between different regions. Since the 1970s, the coexistence of rice and fish had been established based on the traditional system of rice-fish culture. However, reforms in the rice-growing system and progress in rice-fish culture techniques have intensified the conflicts between rice and fish culture. The traditional techniques did not suit the new situation and this hindered the development of rice-fish culture.

In 1972, Ni Dashu of the Institute of Hydrobiology, Academia Sinica, put forth the theory of feeding fish for rice culture. Later Ni Dashu and Wang Jianguo developed a theory of mutualism that stated that rice and fish could coexist. They conducted experiments on rice-fish culture. Ni Dashu studied the rational use of ricefield resources and deemed that although there were differences in growth and development of rice and fish, they shared common characteristics in terms of their need for water, light, and fertilizer.

Fish were fed in ricefields, and fish-raising was integrated with rice culture. Rice was regarded as the main product, and the biological productivity of ricefields was upgraded. Ricefields were used, not only to raise a single crop, but to grow several crops. Rice and fish could coexist in the same field. Bumper harvests of both rice and fish provided more protein, improved efficiency, and increased economic benefits.

In the 1980s, rice-fish culture made progress. Guided by the mutualism theory of rice and fish, scientific and technological workers developed many new techniques for shallow irrigation fields and adjusted the use of pesticides and fertilizer according to the new production structure and to changes in techniques of rice culture. Many new species of fish were used: grass carp, common carp, crucian carp, Beijing bream, silver carp, bighead carp, and tilapia. New techniques were developed that could produce yields of over 7500 kg of rice and 750 kg of fish per hectare.

Rice-fish culture techniques can be divided into three categories: growing rice and raising fish together in the same field, rotating rice and fish, and continuing fish culture in the ricefield after the rice is harvested. In some areas, all three forms are combined. According to engineering facilities, rice-fish culture can be further divided into: feeding fish in furrows and growing rice on ricefield ridges, using ditches, pits, or ditches with flowing water, and additional techniques, such as raising fish and azolla together in the ricefield and raising fish and ducks at the same time in the ricefield.

Rice-fish culture, rotation of rice and fish, and continuous rice-fish culture. In rice-fish culture, rice and fish live together in the same field. This technique can be used with early rice, midseason rice, and late rice. Some contradictions between growing rice and raising fish are unavoidable. Therefore, fertilizer and pesticides that can harm the fish are avoided. Generally, excessive engineering facilities are not necessary. Fish feed is not needed because the fish live on natural food in the ricefield. This is extensive culture. Average production is about 150 kg/ha and well-managed fields can produce over 750 kg/ha. The disadvantage of this technique is that the growth period of the fish is comparatively short and the harvested fish are small. Therefore, large fingerlings are usually used. The technique is occasionally used to stock adult fish for 1 year.

In a rotation of rice and fish, the fallow field left after the rice is harvested is used to raise fish. Generally, fish fry or fingerlings are stocked. After the rice harvest, the straw is left in the field. When the land is irrigated, the straw decays, which makes the water suitable for feeding adult fish. In this form of rice-fish culture, fish have more space to move about and it is convenient to spread feed, but the growth period is relatively long. Compared with raising rice with fish, production of fish is higher. Generally, fish yields are 300-450 kg/ha with maximum yields of over 1500 kg/ha. Because it provides remarkable economic benefits, rotation of rice and fish is widely used in fallow winter fields, during the summer with green manure crops, for stocking fingerlings to produce table fish, and in seedling beds to stock fish fry for fingerling culture.

In continuous rice-fish culture, rice and fish are raised together. Because the fish are raised after the ricefield is fallow, their growth period may be over 1 year, which produces better results. Generally, production reaches over 750 kg/ha. This form of culture is widely used in hilly and mountainous regions.

In practice, a combination of these techniques adapted to suit local conditions achieves the best results.

Other techniques. Fish can be raised quite successfully in furrows in ricefields. This method is based on a half-dry cultivation method developed by Hou Guang-jiong. It effectively transforms uncultivated ricefields and can increase rice production in low-yielding fields (e.g., fields in the foothills, cold fields, and water-logged fields). The ridges in the field can be thickened with layers of soil, and the water in the field can be made deeper. This raises the temperature of the soil, improves soil structure, promotes seedling growth, and improves water management. The fish help reduce diseases, pests, and wild grass and as a result, rice production is increased by 10-20%.

Fish can also be raised in ditches that contain water that is deeper than in the surrounding fields. Fish screens and ditches and pits in the centre of the field help improve the environment for the fish. Fish production in ditches is generally two to three times higher than in level fields.

In integrated fish culture in ditches and pits, pits are dug in the ricefields or along the side of the field and are connected with ditches. Fish are raised in the pits and ditches. This technique was developed after the contract-responsibility system was implemented for family operated rice-fish farms. The method offers several advantages. It improves water management, assures a good harvest, maximizes the use of pits in the field, and helps resolve conflicts between rice and fish caused by operations such as shallow irrigation, drainage of fields, and the use of chemical fertilizers and pesticides. The water in the pits helps the rice resist drought and provides a guarantee of steady rice production. The pits also provide more space for the fish, which enhances fish growth and improves yields.

If the pits are used as nursery ponds, the fry develop into fingerlings earlier, which reduces transportation costs for fingerlings. The pits also provide a capture area during harvest. Production is increased and farmers save work and time.

The technique of raising fish in ditches with flowing water is based on flowing-water aquaculture. It is a semi-intensive rice-fish culture technique that is used mainly in ricefields with good irrigation and sufficient water resources. Wide ditches are dug and a small flow of water is led into the ricefield. Because intensive aquaculture techniques and principles have been adopted, production is comparatively high. Farmers are adopting this technique rapidly in areas with the required water resources.

Rice-azolla-fish cultivation involves growing rice, fish, and azolla at the same time in the same field. This cultivation technique makes full use of space and water. The ricefield provides a good environment and rich food for the fish. Azolla, which grows on the water surface, provides feed for the fish and manure for the field. The fish eat pests and weeds and their excretions fertilize the field to improve the growth of rice.

Several other farming methods have also been developed to maximize the use of ricefield resources and involve rice-fish culture (e.g., growing various beans on the ridges of the field and herding ducks in the ricefield).

Comparison of New and Traditional Techniques

Many developments have been made in the new technique for rice-fish culture. The traditional techniques are integrated into the rice-growing systems found throughout China. This ensures that rice-fish culture is practiced across China. However, the traditional technique does not suit all rice-growing systems. Because there is only one model, it is difficult to extend and develop this model of rice-fish culture throughout all regions of China.

The new techniques include advanced culture and engineering features adaptable to local conditions. Effective engineering facilities help avoid conflicts between rice and fish and improve the ability of the ricefield to resist drought and flood. Rice production is therefore guaranteed along with substantial increases in both rice and fish harvests. The traditional technique cannot resolve or avoid conflicts between rice and fish. Sometimes fish must be sacrificed to guarantee rice production. This reduces income and discourages initiatives in rice-fish culture.

The new techniques apply lessons learned from alternative aquaculture techniques and new developments with respect to stocking size, variety, management, multispecies culture, feeding, and maintenance of water quality using fertilizers. These developments, together with a certain degree of intensification, play a positive role in improving fish production. The traditional technique does not involve these new aquaculture techniques and harvests of both rice and fish are not as good.

The new techniques fully apply the principles of rice-fish mutualism and soil thermodynamics. Different disciplines and the technical systems of farming and aquaculture are organically integrated. The effects and benefits of economics, sociology, and ecology are unified to promote the development of the rice-fish culture system. The traditional technique does not organically combine agriculture with aquaculture. Because the technical system for rice-fish culture is not perfected steady development of rice-fish culture cannot be assured. Moreover, because the new technique has led to increased harvests of adult fish, it has established the technical foundation for rice-fish culture to move from a self-sufficient economy to a commodity economy.

In 1983, the area for rice-fish culture in China was 441 000 ha. In 1987, it increased to 796667 ha with 106 000 tonnes of fish production. At present, the area for rearing adult fish (excluding fingerling rearing) in ricefields is 708 027 ha with a total production of 124 900 tonnes and an average production of 180 kg/ha. This rapid rate of development is directly related to technical advances in rice-fish culture.

Constraints to Rice-Fish Culture

Despite great advances, several technical and production constraints must be resolved:

· The new technique has not been properly extended to farmers and there is a considerable yield gap between experimental models and the yields achieved by farmers. Some models yield over 3750 kg/ha, but farmers obtain yields of 150-300 kg/ha.

· Fry and fingerling supply is insufficient.

· The composition of the species for stocking and stocking density must be more fully studied.

· Feed management must be improved to raise unit yields.

· Weaknesses in fisheries management discourage initiatives taken by farmers in rice-fish culture.

Development of Rice-Fish Culture Techniques

Experience has proven that rice-fish culture is beneficial. Large amounts of fresh fish can be harvested, while the production of rice increases. In some cases, the production value of fish exceeds that of rice. Rice-fish culture therefore offers potential for China, a country with limited land and a large, growing population. The country must develop this potential for food production, while increasing the income of farmers. China’s demand for grain and fish products will likely continue to increase.

There are no marketing problems for the products of rice-fish culture, and income is higher than from growing rice alone. Therefore, farmers are eager to develop rice-fish culture because of the demand for food and the increased economic benefits that can be realized.

Rice-fish culture in China combines the principles of water conservation, soil improvement, and biological control into an integrated technique for rice-fish production. The new technique will play a important role in land management and environmental protection. Rice-fish culture techniques are expected to develop rapidly in several areas.

Basic Techniques of Rice-Fish Culture

The rice-fish mutualism theory advanced the development of rice-fish culture. When other disciplines were integrated into rice-fish culture, the theory was further developed and improved. It is important to study the mechanisms of rice-fish culture, the natural laws governing aquaculture and agriculture, and the interrelationships among rice and fish, and other factors such as soil, water, and fertilization in the ricefield.

Rice Growing and Aquaculture

The study of the interrelationships between rice and fish will help understand the contradictions between the two production systems and find ways to enhance the harmony between agriculture and aquaculture and to improve yields for both rice and fish.

Integrated Rice-Fish Culture Techniques

Rice-fish culture techniques must be integrated with alternative aquaculture (e.g., intensive pond aquaculture, lakes and reservoirs aquaculture, cage aquaculture, and other supporting techniques). This will help increase production per unit area and maximize the widespread practice of rearing fingerlings in ricefields.

Engineering for Rice-Fish Culture

To strengthen the capacity of rice-fish production systems to withstand natural disasters, rice-fish engineering facilities should be integrated with techniques of water conservation. Engineering facilities should also be flexible and adaptable to local conditions.

Management Model for Rice-Fish Culture Techniques

The economic benefits of the different rice-fish culture techniques that are practiced in different areas should be analyzed. Management methods for rice-fish culture must be studied to establish an economic model of rice-fish culture that is adaptable to local conditions, requires less input, but yields increased output.

There are 25 million ha of ricefields in China. Of these, about 10 million ha are suitable for rice-fish culture. If integrated rice-fish farming was further advanced by effective extension work, the area for rice-fish culture in China could be increased by several million hectares within this century. It would then be possible to produce the substantial quantities of fingerlings and adult fish needed to supply further development of freshwater aquaculture in ponds, lakes, and reservoirs. Rice-fish culture will play a vital role in freshwater aquaculture, in the commercial economy, and in agriculture. It will produce food for China and the world.

Zhang Rongquan is with the Chinese Academy of Fisheries Science, Wuxi, Jiangsu Province.

Development of Rice-Fish Farming in Guizhou Province

Shi Songfa

Rice-fish farming has been practiced for over 1000 years in Guizhou. It is most popular in eastern Guizhou (bordering the provinces of Hunan and Guangxi) in areas where communities of national minorities live. The most commonly cultivated species are “Gaopo” common carp and “river” common carp. Farmers gather fish eggs from ponds, ricefields, and rivers and hatch them to get fry. Because of climatic conditions, most areas have only two crops a year with a single crop of rice. Fish are cultivated at the same time as rice. Flat fields and extensive cultivation are the norm. Normally, fields are not drained and the farmers in southeast Guizhou even cultivate fish in the winter water fields. (Note: Winter water fields are ricefields that are left fallow and collect water during the winter. Rice is transplanted to these fields in the spring. This practice is prevalent in the cooler, mountainous areas of western China, particularly in the provinces of Sichuan and Guizhou.)

In 1984, the Departments of Aquatic Products, Soil and Fertilizer, and Agricultural Extension were organized to promote high-yielding techniques for rice-fish farming. A number of technical guidelines, such as Technical Rules for Rice-Fish Farming and Technical Standards for Cultivating Fish in Ridge Box-Ditch Ricefields were published. Many demonstration plots were developed.

By 1987, there were over 3000 ha of high-yield demonstration plots (a 13-fold increase from 1984). The average yield was almost 400 kg/ha (40% more than in 1984). With these encouraging results, rice-fish farming developed rapidly. In 1980, 42700 ha of ricefields yielded 3348 tonnes of fish, by 1983, this had increased to 60 000 ha and 4611 tonnes of fish. In 1987, there was a 75% increase in area and a 210% increase in yield (74 700 ha and 10 400 tonnes of fish). This amounted to 57% of the total fish production of Guizhou in 1987. The unit yield also increased 78% from 1980 to 1987 and reached 139 kg/ha.

Development Trends

With popularization and technical extension, rice-fish farming has improved the ecological environment of the ricefield and is making better use of the carrying capacity of the field and achieving additional benefits from low-level inputs.

New Rice-Fish Farming Techniques

Flat-field techniques of rice-fish farming have been replaced by ridge-ditch ricefields (in which the fish are grown in the ditches and the rice is grown on the ridges), box-ditch fish raising, and manure-pit fish raising in flat fields. Instead of farming fish only with rice, farmers now also grow wild rice or lotus.

Fish farming in the ridge-ditch fields does not require inundated irrigation, therefore, the conditions of water, fertilizer, oxygenation, and heat are improved in the soil. This has considerable impact on the rice. It stimulates the early growth of seedlings and early emergence of tillers. The grains of rice increase in number and size, which produces higher yields. This practice also increases field-water storage, improves drought-resistance capability, and provides sufficient deep water for fish. These factors all improve fish growth and lead to higher yields.

The Scientific Association of Southeast Guizhou Prefecture, the Information Institute of Scientific Committee, and the Prefecture Agricultural Institute conducted experiments in 1986 to observe the differences between ridge-field rice and flat-field rice. They found that there were considerable changes to the soil environment that affected the growth of the rice plants. Soil temperature in ridge fields was normally 0.2-0.4°C higher than in the flat fields. Results were particularly obvious in cold, muddy fields that had low soil temperatures. Growth was faster in ridge-rice cultivation. Seedlings recovered quickly after transplanting and tillers emerged 9 days earlier than in flat fields. The activity of soil microorganisms was also enhanced, which improves the breakdown of soil nutrients and helps provide adequate nutrition for root growth. With improved vitality, rice roots grew deep into the soil and the roots were stronger. During the tilling period, rice roots in the ridge fields were 8 cm longer than that in flat fields, and on average there were 20 more roots. During the full-ear period, the roots of plants on the ridges were 13 cm longer and there were 199 more roots. Ridge-rice cultivation can also enhance the resistance of the rice plant to drought and lodging. When fish and rice were grown together, topsoil fertility in ridge fields was significantly higher. There were increases of 0.55% in organic matter, 0.022% in whole nitrogen, 1.2 mg/100 gt in hydrolytic nitrogen, and 27.7 ppm in effective phosphorus.

Experiments carried out in 1986 by the Aquatic Products Station of Chishui County revealed that ridge-rice cultivation could improve rice tillering and increase average grain weight. In these experiments, the average number of grains per ear in the ridge fields was 140-155 compared with only 105-110 in flat fields. The average weight of 1000 grains in the ridge fields was 27.5-28.4 g, compared with 26.5-27.0 g for flat fields. The empty grain rate was 26.5-28% in the ridge fields and 39-41% in the flat fields.

Additional evidence of the benefits come from farmer experiments. A farmer, Jiang Chengxu in Suiyang County, conducted a comparison trial in an area of 0.05 ha (0.025 ha for each of the two methods). In each area, he stocked 200 7-cm fingerlings. The flat field yielded 170 kg rice and 12.6 kg fish. The ridge field yielded 200 kg rice and 34 kg fish, or an increase of 18% for rice and 172% for fish. In the Southeast Guizhou Prefecture, ridge-field cultivation required 6-8 more farmer-days of labour, but the value of production increased by 50%.

Raising of fish in box ditches and manure pits in flat fields can also create a good ecological environment for fish because pesticides are not applied and exposure to sun and drought is reduced. This system increases the potential of the ricefield and produces higher fish and rice yields. Manure pits normally only occupy 10% (or less) of the ricefield and poses no threat to rice production. Chishui and Songtao Counties have carried out rice-wild rice-fish and rice-lotus-fish experiments. Production values were CNY 3809/ha in Chishui and CNY 4170/ha in Songtao. (Note: In October 1988, 1 United States dollar = 3.72 Chinese yen and 1 Canadian dollar = 3.19 yen.)

New Species

Instead of raising only common carp, farmers now raise several fish species. The temperature of shallow water in ricefields changes with air temperature and is unstable. However, during the warm season, leaves of the rice plants shade the water surface and stabilize the water temperature. This creates a suitable environment for growing grass carp, common carp, silver carp, variegated carp, tilapia, and crucian carp.

The ricefield is an artificial ecosystem that abounds with various grasses, weeds, plankton, and other organisms. If only common carp are grown, these resources are not fully utilized and yields are not very high. In recent years, several species have been raised together and the results have been encouraging. This demonstrates that the ricefield ecosystem is suited for polyculture of fish. Normally, common carp are raised with grass carp or silver carp, grass carp with tilapia, or common carp with crucian carp and catfish. Either fry or adult grass carp can be raised.

With the appropriate number of fish, rice seedlings are not eaten by the grass carp. The fish consume grass and weeds to the benefit of rice growth. For example, 2250-3000 grass carp and common carp (in the ratio of 4:6 of 10-cm fish) can be raised in 1 ha without damage to seedlings. When the fish have grown to 17 cm in length and are able to eat seedlings, the rice plants are tall enough to avoid damage. If the grass carp are over 20 cm in length, 450-750 fingerlings can be put into a 1-ha ricefield. In this case, additional feed (grass) must be provided during the early stage to keep the grass carp from eating the rice seedlings. If silver carp and variegated carp are raised, their number should be limited to 5-10% of the total number of fish raised.

In Huangping County, farmer Yang Zaigui raised fish in a 0.08-ha ricefield. On 12 June 1988, he stocked 49 grass carp fingerlings (8.9 kg), 372 common carp fingerlings (18.4 kg), and two silver carp fingerlings (0.6 kg). After 105 days, he harvested 34 grass carp (31.15 kg), 356 common carp (66.9 kg), and two silver carp (1.81 kg). Total net production was 73.05 kg. Yield per hectare was 906.8 kg fish and 7875 kg rice.

Species Improvement

Local common carp have been replaced with hybrid common carp. The trend is toward improved species. Local Gaopo carp has long been raised in Southeast Guizhou. It is docile, quiet, and usually does not jump. During floods, it does not panic and swim away. It hides in muddy rice water when disturbed. However, its quality is deteriorating because of poor selection of brood stock. Parent fish are so small that their offspring do not develop properly.

In 1985, the Aquatic Products Bureau of Leishan County sampled 50 Gaopo carp. The heaviest one was 350 g and the smallest 25 g. Five of the fish that weighed 25-95 g were mature. Work by the Aquatic Products Bureau of Luping County revealed that this fish is sexually mature at approximately 100 g. Results from the Aquatic Products Bureau of Guiyang City showed that 35% of the fish with an average weight of 185 g were sexually mature. This suggests that Gaopo carp have seriously deteriorated and are maturing at a small size. Since 1980, many localities like Zunyi, Chishui, Wuchuan, Zheng’an, Jinping, and Tianzhu have worked to improve carp varieties. While paying attention to the selection and improvement of local varieties, they have also introduced improved brood fish.

In 1983, the Aquatic Products Bureau of Zunyi Prefecture introduced parent fish of two common carp varieties, Yuanjiang carp and Wuyuanhese red carp. They achieved good results when they released the hybrid Heyuan carp from these two varieties. In 1988, the Aquatic Products Bureau of Luping County compared improved common carp and local common carp. Growth characteristics were evaluated by taking five samples at monthly intervals after release. Improved common carp gained 1.95 g more each day and relative growth was 1.5% higher. When the improved common carp weighed 520 g each, the local common carp weighed only 200 g (40% less).

In 1987, the entire province began the systematic improvement of common carp. In 44 variety improvement sites, 31.4 million fry and 9.8 million fingerlings of improved common carp were produced. A total of 967 ha of ricefields received this variety and results were good.

Intensive Cultivation

Intensive cultivation of fish is now replacing extensive cultivation. Extensive cultivation only uses natural feed; therefore, yields are low. In 1980, the provincial average yield of fish was 78.3 kg/ha. To achieve high yields, traditional culture systems must be replaced with intensive culture systems that make full use of the carrying capacity of the ricefield ecosystem. Farmer Lu Binlun in Danzai County conducted a comparison trial in 1985. Intensive culture yielded 1242 kg of fish per hectare or 4.6 times more than extensive cultivation (220.5 kg/ha). In 1983, farmer Liu Dingzhong of Longquan Township raised fish in a 0.32-ha ricefield using earthworms and maggots as additional feed. He harvested 580 kg fish or 1812 kg/ha. In 1984, farmer Li Xingji in Suiyang County harvested 325.4 kg from a 0.21-ha field by using wastewater from factories.

Prospects

Guizhou Province is a subtropical area with a humid monsoon climate. It has low latitudes and high elevation. The temperature is relatively high in winter but low in summer. The yearly average temperature is between 14°C and 16°C in most areas. The temperature is above 10°C for 220-240 days a year, and 270 days are frost-free. Annually, there are about 180 rainy days, 1100 mm of rainfall, and 1200 hours of sunlight. There are many cloudy and rainy days and yearly changes in light, heat, and water are synchronized. All these conditions are conducive to growing rice and fish. The longer growth period for fish and the good overwintering conditions allow a sound farmland ecosystem can be established to increase the production of rice and fish.

Ricefields in the province cover a total area of 791 000 ha, over half (about 400 000 ha) of which are low-yielding fields. There are 122 000 ha of winter water fields. These areas are, to various degrees, poor, barren, highly acidic, sticky, sandy, muddy, and cool and therefore do not produce high yields of rice. Fish farming improves the soil and rationally uses the land to produce more rice. Fish farming is profitable and has the potential to improve the economic situation of farmers, particularly in mountainous areas.

In 1984, a survey was conducted of 20 farming households in Danzai County that covered about 1.32 ha of rice-fish farms. The output of fish and rice was valued at CNY 4374/ha, 90% more than rice cultivation alone. Surveys in Danzai and other counties showed that rice-fish farming increased the output value of ricefields by CNY 817.5/ha.

In the future, rice-fish farming will undoubtedly supply a large portion of the fisheries production in Guizhou, especially in mountainous areas where there are large ricefields but few ponds or reservoirs. It is important to develop rice-fish farming and to establish systems for technology extension and for the production and supply of improved varieties. Ridge-ditches, box-ditches, manure pits in flat fields, and other forms of rice-fish farming should be adopted to suit local conditions. Improvement of the common carp variety must continue. Mixed culture of species (mainly common carp and grass carp) should be practiced. Intensive cultivation should replace traditional extensive cultivation, which usually has low yields with low input. Improved fish-farming techniques should be adopted in a systematic way to make the best use of ricefield resources and to improve fish yields.

Shi Songfa is with the Aquatic Products Division, Guizhou Aquaculture Bureau, Guiyang, Guizhou Province.

Reforming Rice-Fish Culture Technology in the Wuling Mountains of Eastern Guizhou Province

Chen Guangcheng

In the past, traditional methods of rice-fish culture were used in the Wuling Mountains. Because output was very low, several reforms were undertaken to improve rice-fish culture.

Improving the Environment for Fish

Depending on the type of soil, furrows, wide ditches, or pits were dug to culture fish in flat ricefields. In cold, muddy, fertile fields, rice-fish culture can be carried out in furrows and wing ditches. The ridge of the furrow is normally about 26-cm wide and the ditch about 39-cm wide and 26-33 cm deep. In muddy fields, where it is difficult to make ridges, wing ditches were introduced. The wing is 2-m wide and the ditch about 0.8-m wide and 0.5-m deep. This innovation improves soil structure, light, and temperature and increases rice production.

In 1985, these innovations were tested at 54 sites (13.7 ha). The dry rice yield averaged 6712 kg/ha (18.% more than in flat fields). Ditches help solve problems created by shallow water and variations in water temperature in flat fields because they increase the volume of water by about 100%. In summer, changes in water temperature are 2-3°C lower than in flat fields. This improves the environment for the fish. In these tests, average fish yield was 507 kg/ha. In high-yielding fields that can produce 7500 kg of rice per hectare, fish production is often 750 kg/ha. In 1987, a 1.5-ha field averaged 7605 kg of rice and 825 kg of fish (average weight per fish 0.85 kg).

The farmers are given these instructions to implement the new technology:

To culture fish in a field, dig a pit big enough to make up 5-10% of the field. The pit should be 1.5-m deep and it should link to the fish ditch. There is four times more water in this field than in flat fields. This not only benefits fish growth, but increases the quantity of fish and provides the convenience of dry fields, where farmers can apply additional fertilizer and agricultural pesticides.

In terraced fields, a big side ditch is dug in the back ridge. The side ditch should be 1-m wide and 1-m deep and should be linked to the fish ditch. This enhances the growth of rice, which benefits from warmth, and the fish, which like the water. These changes provide conditions for high yields in rice-fish culture.

Stocking Large Fingerlings and Late Harvesting

In the past, the fish species were usually breed and cultured by the farmers. Most of the strains have degenerated. A system of elite breeding has now been established based on the district and township fish hatcheries (e.g., there are 104 sites in Yinjiang County).

Instead of small fingerlings, 250-300 large (about 10 cm) fingerlings are stocked in the fields. Fingerlings should be stocked before the seedlings are planted (from February to April). This allows the fish to obtain food when plankton is abundant. Experience has shown that the same-size fingerlings stocked before planting rice seedlings weigh 100 g more than fingerlings stocked after planting.

Keeping water in the fields when the rice is harvested allows the fish to grow for an additional 60 days and to increase their weight (to about 150 g). During this period, the rice that falls into the field and the young rice seedlings that grow from the roots of the rice are good food for fish.

In February 1987, Li Demin, a farmer in Yundu Township, Jiangkou County, put 200 grass carp and 200 common carp, each about 15-cm long, into a 0.2-ha field. In May, he put 1800 small fingerlings into the same field. On 19 October, he harvested 162 kg of adult fish and 31 kg of fingerlings. The adult fish averaged 0.52 kg and some were as large as 1.6 kg. The average yield was 986 kg of fish and 6358 kg of dry rice per hectare.

Polyculture and Intensive Culture

In mountainous areas, the fields are poor and weedy; therefore, a polyculture of grass carp, common carp, and silver carp is used in the ratio of 3:6:1. From May to July each year, 15 000 small fingerlings of grass carp and common carp are stocked per hectare of field. By November, the fingerlings reach a length of 12-18 cm and the survival rate is 20-30%. Weeding is not necessary in fields devoted to polyculture.

In intensive culture, a base fertilizer is applied before the fish are stocked into the fields. From April to May, it is not necessary to feed the fish because they are small, water temperature is low, and benthos and weeds are plentiful. From June to September, feed should be applied once a day. After the rice is harvested, the quantity of feed should be reduced.

Scientific Water Management, Proper Irrigation, and Drainage

The basic principal is to consider the needs of both the rice and the fish. When fingerlings are stocked before the rice seedlings are planted, the water level should be maintained to minimize fish deaths. Five to seven days after the rice is planted, the water level should be reduced to promote tillering. In a furrow or ridge system, the water should flood the roots of the rice seedlings. When the rice seedlings begin to turn green, the water level can be reduced. This will not affect the fish because they are still small.

A month after rice seedlings are planted, the flat fields should be drained for weed control. Later, the rice water level should be raised to about 12 cm to control ineffective tillering of rice and to benefit fish growth. After the rice is harvested, the water should be raised to over 50 cm for continuous fish culture.

Economic Benefits

These technical reforms have produced economic benefits (Tables 1-3).

Value of Output

In 1986, 8.6 ha of ricefields produced 53 771 kg of dry rice, valued at CNY 32 262 (Table 1), or an average of CNY 3840/ha. In 1987, with rice-fish culture, these fields produced 6020 kg of fish valued at CNY 36121 and 55 286 kg of rice valued at CNY 33 171. The total value of production was CNY 69 292, or an average of CNY 8249/ha, which was 2.1 times more than in 1986 without fish culture.

Ratio of Investment to Income

In 1987, CNY 7567 was invested in rice-fish culture, an increase of CNY 5252 from 1986. But in 1987, net income was CNY 61 725, which was CNY 31 778 more than in 1986 (Table 2). The ratio of investment to income from rice-fish culture was 1:6.

Rate of Return

In 1986, net income was CNY 29 947. In total, 1403 workers were employed and each produced an output value of CNY 21.34. In 1987, net income was CNY 61 725, which was achieved with 2290 workers; therefore, each produced an output value of CNY 26.95 or CNY 5.61 (26%) more (Table 3).

Value of Fish

Before the reforms in rice-fish culture, fish from the fields weighed about 100 g each. Because the species had degenerated, they could only be sold for food for about CNY 2/kg. After the technical reforms, 11 780 fish were caught from 8.4 ha of ricefields. Total weight was 6020 kg, or an average of 0.51 kg/fish. These fish fetched a price of CNY 6/kg; therefore, the commodity value of the fish increased three times after the technical innovations.

Chen Guangcheng is with the Bureau of Aquatic Products, Tongren Prefecture, Guizhou Province.

The Development of Rice-Fish Farming in Chongqing City

Xu Shunzhi

Rice-fish farming has been conducted for over 1000 years in the city of Chongqing. For a long time, however, fish yields were poor and unstable because of extensive cultivation, traditional methods, and a variety of limiting factors. Advances in science and technology, the development of the fish industry, changes in the structure of rural industries, and an increase in the commodity market led people to seek new ways to maximize water resources. They pursued new productive technologies that changed the traditional system of rice-fish culture and produced economic, social, and ecological benefits.

The productivity of rice-fish farming in Chongqing has been improved by engineering installations, new technologies for rice-fish farming, and improved circulation of nutrients and energy in the water. The contribution of rice-fish farming to total fish production in the city increased from 2-4% in the 1970s to 29% in 1987. In 1987, rice-fish farming ranked second as a method of fish production and was conducted on 73 300 ha of ricefields that produced 10 200 tonnes of fish. New cultivation technologies were practiced on 22 250 ha of the total area and produced 6680 tonnes of fish. Some demonstration fields produced 3000-4500 kg/ha. Total production from rice-fish farming was valued at more than CNY 50 million.

Rice-Fish Farming in Chongqing

Chongqing, in eastern Sichuan Province, has a subtropical monsoon climate with adequate heat and rainfall during the warm season. The average temperature is 17.5 -18.5 C, and there are 1000-1100 mm of rainfall, 320-340 frost-free days, and 1200-1300 h of sunshine. These conditions are suitable for the cultivation of fish.

For many years, production from rice-fish farming remained poor and unstable. Improvements were not made because of political changes, faulty economic policies, changes in farming systems, primitive cultivation technologies, traditions that were difficult to change, and damage from natural disasters. The area devoted to rice-fish farming eventually decreased to less than 4000 ha with a total production of only 300 tonnes. New cultivation methods that used trenches and sumps were introduced before the 1980s, but results were limited because the trenches were small and the pits were shallow. During the hot, dry season, conflicts between the water requirements for rice and fish could not be solved.

However, recent improvements in the rural-responsibility system, the extension of rice-fish culture technology and the commodity market, and new economic benefits have encouraged farmers to develop rice-fish farming. The units responsible for developing aquatic products advocated, demonstrated, and extended advanced fish-culture technology. These efforts contributed to the rapid development and increased productivity of rice-fish farming in Chongqing (Table 1).

To increase production, a variety of methods were studied and adapted to local conditions of topography, terrain, water quality and temperature, soil, and vegetation. The goal was to enhance the growth of both rice and fish and to achieve bumper harvests of both crops. Gradually, fish culture in ricefields was developed and promoted through demonstrations and extension, and an increased number of farmers adopted the new technology. Farmers started to stock fish rather than depend on natural populations. Ricefields produced multiple, instead of single, crops. The management and administration systems for fisheries were also improved.

Cultivation Models of Rice-Fish Farming

In rice-fish farming, both rice and fish live in the same body of water and help each other by creating a favourable living environment that meets their physiological needs. Optimum conditions include the correct temperature, proper quality and depth of water, and appropriate nutrients and feed. The methods of cultivation must promote stress resistance.

Chongqing is located in the hills and low mountain areas of Sichun Basin where ricefields are widely distributed and natural conditions vary. Several methods of rice-fish farming have been established to suit local conditions.

Flat fields (or fish sumps and trenches). Ricefields with good water resources, irrigation, drainage, and stable water (despite drought or excessive rain) can be used for fish culture. The height of the ricefield dikes is raised to above 0.5 m and reinforced to prevent collapse and leakage. Bamboo screens are installed to prevent the fish from escaping through irrigation and drainage holes, which must be higher than the level of the field. Sumps and trenches are dug before seedlings are transplanted. Usually, ditches are dug around the edge of the field. If the ricefield is larger than 0.07 ha, a cross-shaped ditch should be dug in the middle; if the field is more than 0.3 ha, a ditch in the shape of a double-cross (#) should be dug. In the lower part of the field where the surface is not smooth, 1-m deep trenches are scooped out along the water inlet or the cross. The number of trenches varies according to the size of field. Fish varieties are 70-80% common carp and crucian carp and 20-30% grass carp. The total stocking rate is 3000-4500 fry per hectare (using the previous years stock). Production is 150-600 kg of fish per hectare.

Fish ponds. Fishponds are dug in the back edge or a secluded spot in the ricefield. The size and number of ponds depend on the size of the field. The bottom of the pond should be at least 1 m lower than the level of the ricefield. A stone wall is built around the pond to prevent it from collapsing. In ricefields of more than 0.1 ha, ditches (70-cm wide and 50-cm deep), should be dug to connect the ponds. Stone breaches between the ponds and ditches hold fish screens and prevent collapse. A 10-cm pipe is sometimes installed in the pond bottom to improve drainage and management. The fish varieties stocked include common carp, crucian carp, and grass carp, in equal proportions. Some silver carp and tilapia are also stocked. From 1982 to 1985, there were 5880 ha of fishponds in Dazu County, Chongqing, with an average production of 547.5 kg/ha.

Fishponds are used mainly in winter water fields and in deep-mud fields and water-logged fields where rice production is low. The specifications for ditches and banks should be based on the fertility of the field, the farming system, and the rice varieties. The ditch is usually about 80 cm wide. The field is normally not ploughed and the bank is built 7 days before transplanting to a height of 20-25 cm or 30-40 cm. The field should not be drained dry, the banks should be even, and the ditches straight and connected. A small bank is built, and a row of seedlings is transplanted onto this bank. The ridge should be reinforced before the bank is built to prevent fish from escaping. There should be a fish screen in the irrigation and drainage holes and the width of the breach should be according to the size and drainage volume of the field. The time, varieties, and size of the fingerlings should suit local conditions. Common carp or grass carp are the main species, but some tilapia are cultivated later in the year. Production is about 600-750 kg/ha.

Semiarid plus pond. This method is suitable for use with semi-late rice. The height of the dike is increased to 0.6-1 m and the dike is strengthened. A ditch for flood drainage and an opening are dug and fish screens are installed. About 5% of the field is used as a fishpond (1-1.5 m deep). Before the seedlings are transplanted, a ditch (35-cm wide, 25-cm deep) and a bank (25-cm wide) are constructed. When the seedlings have turned green, the natural feed is supplemented with prepared feed and 80 common carp, 80 grass carp, 40 silver carp (6.6-cm fingerlings), crucian carp, and tilapia are stocked. Production can reach 750-2250 kg/ha.

Ridge-ditch system. Ridges and ditches are dug, based on the size of the field, available water resources, sunlight, and wind direction, to bring the edge effect into full play to increase the rice production. Ridges are 1.1-m wide (transplanting five rows of seedlings) or 0.8-m wide (transplanting four rows of seedlings); and ditches are 35 cm wide and 25-35 cm deep. Depending on the size of the field, one or two horizontal ditches are dug to connect all the ditches and improve the flow of water. This increases the volume of water for the fish and improves the capacity of the field to store water. Fish are stocked at 4500-7500/ha as 3-cm fingerlings that include 30-40% grass carp, 50-60% common carp, and 10% silver carp. Production is 750-1500 kg/ha.

Wide ditch around the field. A 1-m wide ditch in the shape of a cross is dug around and through the field. Both ridged and flat fields are used. Methods are similar to other systems. Production is 450-750 kg/ha.

Farming with fish cultivation. This method is also called the seven layers production of rice-fish cultivation. Sugarcane is grown in the ridges of the field and rice is transplanted into the field. Wild rice is planted between the rows of rice, and water chestnuts or water hyacinth are cultivated on the water surface. In the water, fish are cultured in three layers: silver carp in the upper layer, grass carp in the middle layer, and common carp or crucian carp in the bottom. Fisheries engineering is the same as for other methods. This method is based on ecological principles and achieves a balance between plant growth and fish culture and better economic benefits (Table 2).

Cost-Benefit Analysis of Rice-Fish Farming

Rice-fish farming is an effective way to make full use of ricefield resources and to cultivate freshwater fish. It offers remarkable advantages: it does not require the use of other land and water bodies, it has a short cycle, requires small capitalization, gives fast results and benefits, is easy to manage and uses simple technology. It also fully uses the productive potential of water in the ricefields. A 1984 study of rice-fish farming in Chongqing by the Bureau of Agriculture, Animal Husbandry and Fishery, provided data from 153.4 ha of winter ricefields in four counties near Chongqing (Table 3).

In 1984, the production of fish was 701 kg/ha and rice production was 7640 kg/ha. The net income of rice-fish was better than other cultivation industries. Through demonstrations and extension, small areas of rice-fish culture were enlarged into productive bases of commercial rice-fish farming that incorporated pond cultivation and reservoir fishery. Rice-fish culture has become one of the three pillars of the fishery in Chongqing.

Advantages and Limiting Factors

In agriculture, ecological and multiple uses of land should not be overlooked. Rice-fish cultivation can improve the ecological environment of the field, while providing economic benefits. It makes good use of water resources in the ricefield, decreases competitors in the waters, makes reasonable use of fertilizer and sunlight, and improves the fertility and permeability of soil. It can also inhibit or eliminate weeds in the field. Rice diseases and insect pests are reduced and fish wastes are a good manure. Extensive rice-fish cultivation helps prevent floods, increases the resistance of the rice plant to drought and strengthens the regenerative ability of the ecological system.

In over a decade, the rapid development and multiple cultivation models of rice-fish farming have also provided direct benefits to Chongqing:

· A suitable natural environment - There are 460,000 ha of ricefields in Chongqing and about 40% of these can be used for fish culture. Because Chongqing is the main city on the upper Yangtze River, there is a growing demand for aquatic products.

· Productive technology - Chongqing now has several production units in aquatic science and technology and in fisheries who are working to develop rice-fish farming.

· Enthusiasm of leaders and farmers - Rice-fish farming is an aquacultural development project of national importance. Because bumper harvests in both rice and fish have increased the income of farmers and stimulated the rural economy, rice-fish farming now appeals to farmers.

Several factors limit rice-fish culture: naturally occurring floods and droughts and environmental conditions such as terrain and water temperature and quality. Anthropogenic factors also limit rice-fish farming: lack of fry and fingerlings, the need to popularize science and technology through extension, and the difficulty of changing traditional production methods.

Xu Shunzhi is with the Chongqing Bureau of Agriculture, Animal Husbandry and Fishery, Chongqing, Sichuan Province.

Development of Rice-Fish Farming in Jiangsu Province

Xu Guozhen

Jiangsu Province is located along the coast of the Yellow Sea and is situated in the lower reaches of the Yangtze and Huai He rivers. Its mild climate and abundant rainfall make this region ideal for growing rice and fish. Jiangsu Province has 2.4 million ha of land for rice cultivation and about 670 000 ha of water surface for fish production, which makes it one of the important rice and fish producers in China. There have been substantial developments in rice-fish farming in Jiangsu Province and farmers are becoming more familiar with the new practices.

Current Situation

Since 1982, rural economic reforms have spread and the industrial structure has been readjusted. Rice-fish farming in Jiangsu Province grew rapidly during this period. In 1983, the area for rice-fish culture was 1000 ha; by 1987, 13 000 ha of ricefields were devoted to fish farming. The practice was adopted mostly in the Lixiahe region in North Jiangsu and in the hilly country in the centre of South Jiangsu.

Most farmers incorporated fish farming with midseason or hybrid rice; a few rotated rice and fish or cultivated them in succession. Farmers also developed their own ways of raising fish to suit the local conditions, topography, traditions, and fish species. These included digging fixed fish pits, connecting ricefields to out-field ditches and ponds, polyculturing different species, breeding summer fry in ricefields, and cultivating rice with fish and freshwater mussel.

The extension of new farming techniques brought vitality to the development of rice-fish farming in the whole province and upgraded the level of intensive farming. The average yield of fresh fish increased from 150 kg/ha in 1984 to 300 kg/ha in 1987. Yields were even higher in some areas. In 1985, 190 ha of ricefields produced 750 kg of fish per hectare; whereas, in 1986, a similar demonstration area of 270 ha produced the same yield of fish.

In 1987, high production demonstration farms were established in Funin, Jianhu, and Hai’an counties. Each farm was 670 ha and produced an average fish yield of 705 kg/ha. From 1984 to 1987, the area for rice-fish culture in the province rose to 40 000 ha with a total commercial fish yield of 1630 tonnes, plus a fry yield of 6140 tonnes that could be used to produce 2400 tonnes of commercial fish. The total value of fish production was over CNY 100 million.

However, in comparison with other provinces, rice-fish farming in Jiangsu has developed slowly. The area for rice-fish culture decreased from about 13 000 ha in 1987 to 6000 ha in 1988. The main reasons for this decrease were:

· The high-yielding techniques for rice-fish farming were not adequately extended or widely adopted, which resulted in poor management. In rice-fish farming, extra care is needed in pesticide application and drying of the ricefield because these can adversely affect fish growth. Other factors that can affect rice growth must also be considered carefully: fish species, fish size, size of water body, and the type of ditches and pits. However, in practice, some farmers found it hard to change their cultivation traditions, found themselves short of labour at the time of planting and harvesting, or did not take sufficient care. Because of poor management, high-yielding techniques could not be fully applied and this reduced unit yield.

· The actual recovery rate was low. At present, the mechanization level in grain production is low and irrigation facilities in many areas are poor. In addition, under the current household-management system, management of a piece of land often involves several households. This creates difficulties and weakens the ability of the farmers to deal with natural disasters such as drought or flood. From 1984 to 1987 only 67-70% of the rice-fish farming areas were harvested.

· Production and extension services were not well organized and there was a lack of channels to provide farmers with inputs such as fry and chemical fertilizers. Some farmers could not sell their fry, which were produced too early to be used to stock ponds and reservoirs. Furthermore, because reproduction quantity and output value were low, benefits from fish farming were not significant. At the current yield level of 300-375 kg/ha, unit income is CNY 1200-1500/ha. A farmer household normally only has up to 0.7 ha for fish farming, which would yield only a few hundred yuan. This is not attractive, particularly in regions where there are many other economic options.

Ways to Further Develop Rice-Fish Farming

Introduce Appropriate-Scale Management

Economic benefits from rice-fish farming should be improved. Because the rural economy is developing rapidly, employment opportunities are increasing and some farmers opt to leave their land for other undertakings. Improved productivity allows other farmers to farm larger areas and to produce much more grain. This new kind of farmer provides the basis for larger-scale management and makes it possible for farmers to make long-term plans. This, in, turn enhances their ability to cope with nature-induced difficulties and to mass-produce products, which improves the supply to city markets. Appropriate-scale management is conducive to specialization and commercialization in the rural economy, brings economic benefits to farmers, can lead to ecological benefits by improving soil fertility, and can help reduce pesticide application and pollution.

There are two types of management in fish farming. In one type, specialized households or individuals raise fish, while individual households plant rice. In this case, specialized fish-raisers take care of water management and fish farming, while other farmers plant and manage rice. The fish pits and ditches are dug by the rice-planters. A village committee takes charge of the general production arrangement. The income from fish farming is distributed among the fish-raisers, the rice-planters, and the committee in the proportion of 7:2:1. This system makes management easy, allows for a large area (10-30 ha) for raising fish, and provides satisfactory benefits to those concerned. A specialized fish-raiser can earn several thousand yuan each year.

The second type of management concentrates fish farming and rice growing in a single household and depends on available labour, mechanization level, and the farmland arrangement of the household. Generally, the farms cannot be too big (about 2 ha per household). About 10 tonnes of grain and CNY 2000 from fish farming can be produced each year.

Improve Production Conditions and Facilities

Adequate construction work and facilities are essential not only for fish survival in ricefields but for bumper harvests of fish and rice. Given the precondition of not affecting rice yields, the better the construction work, the higher the fish production. With good construction, conditions it is also easier to resolve the contradictions between rice growing and fish farming and to tackle natural difficulties.

Various types of constructions are made for fish farming in different rice-farming systems. In high-yielding areas of Jiangsu Province, several practices are adopted:

· Farmland is rearranged to expand the fish-farming water surface and increase fish-carrying capacity while trying to reduce the area for fish ditches and pits. This can be done by combining in-field with out-field construction. For example, in-field fish ditches can be connected to out-field water inlet-outlet ditches, natural pits, and ditches beside roads and tractor paths. To better use in-field ditches, multiple uses can be made of ditches and pits in rice and wheat fields.

· Appropriate pits and ditches are made in ricefields. These pits and ditches should be simple in form and relatively close to each other. The surface proportions of the pits and ditches are 7:3 or 6:4 and the pits are 1.2-1.5 m deep; the ditches 0.45-0.06 m deep. This increases the size of the water body and its fish-carrying capacity. Normally, pit and ditch surfaces occupy 10% of the ricefield.

· Fish pits and major ditches are dug in a single operation before rice is planted. The advantages are: much of the work can be done during slack seasons in connection with other projects such as irrigation system construction, road construction, and house building. This not only saves labour, but also reduces labour shortages during the busy season. Furthermore, these larger pits can be used for early season fry and late season fish.

Adopt Comprehensive Measures to Prevent Escape of Fish

The key to better economic benefits from rice-fish farming is to increase the actual catching rate. Fish escape in several ways: because of floods and overflow of water, through damaged or poorly placed fish screens, and through holes dug by rats and eels.

To prevent fish from escaping: dikes should be high enough to keep fish-farming fields from flooding, ricefields should be well equipped with irrigation and drainage facilities, fish screens should be firm and durable and be placed appropriately in water exits and entrances, field ridges should be 0.4-0.6 m high and not leak, and strict management should be practiced to ensure that prompt action can be taken when problems arise.

Adopt Intensive Farming Measures

Technical guidelines for high-yielding rice-fish farming need to be developed and promoted using some of the experiences gained from pond-fish rearing:

· Fish species adapted to the specific needs of different areas must be selected and used. In Jiangsu, several options could be considered. Farmers with large areas of water and large numbers of fingerlings can: mainly breed fingerlings of grass carp and common carp, and aim for a fingerling yield of 600 kg/ha; or mainly breed fingerlings of grass carp and common carp, plus 1-year-old fingerlings of a fast-growing species (e.g., tilapia or hybrid common carp). The target yield for fingerling and commercial fish is 750 kg/ha. When the area for fish breeding is small, when breeding is for producing commercial fish, or when there is no temporary pond for fingerlings, farmers can: mainly breed Megalobrama amblycephala, plus a small number of fingerlings (yield could reach 750 kg/ha); or mainly breed mature carp with a target yield of 750 kg/ha. Fish growth should be enhanced with supplemental feeding. To gain better results, additional weeds, duckweed, and commercial feed are needed to improve fish growth. Frequent water renewal is also needed to improve water quality, particularly after land baking and pesticide application, when the water body for fish is small, and when organic matter content is high. The added water increases oxygen, improves feed consumption, and reduces the concentration of pesticides. Daily field monitoring is also needed to raise the survival rate by preventing problems such as pollution, and loss of fish by escape, theft, of attacks by natural enemies.

· Increase the number of species that are raised. Currently, only commonly bred fish species are raised in ricefields, although some farmers are exploring ways of breeding specialty aquacultural products such as clams, shrimp, and mandarin fish. These measures may help improve economic results; however, the farming techniques must still be developed and are experimental.

Xu Guozhen is with the Bureau of Aquatic Products, Nanjing, Jiangsu Province.

Rice-Fish Culture and its Macrodevelopment in Ecological Agriculture

Yang Jintong

Agricultural production is, in essence, a process of recycling materials and converting energy. Through this process, the natural functions of animals, plants, and microorganisms are applied to produce food and other basic necessities. There are two major trends in the development of contemporary science and technology: toward in-depth analysis and specialization, and toward integration, which is broader but less specialized. Integrated development of agriculture and food production is an important strategy that makes full use of agricultural resources and promotes the rational development of the agricultural ecosystem.

Experiments and experiences have repeatedly shown that adding fish to the ricefield ecology helps increase production and achieves social, economic, and ecological benefits. Rice-fish farming is, therefore, a primary option when trying to develop ecological agriculture.

Benefits of Rice-Fish Farming

Nonbiological factors (e.g., water, soil, light, heat, and air) and biological factors (e.g., animals, plants, and microorganisms) are interrelated and interdependent. They form an ecosystem with unilateral functions. When one factor changes, it triggers a chain of reactions. According to the principles of ecology, the structure of the food chain in a system has a direct impact on the net output of the ecosystem.

The farmland ecosystem is an anthropogenic system that is regulated to increase its output. In the biological community of the ricefield ecosystem, rice is predominant; weeds, plankton, humus, and photosynthesizing bacteria are the primary producers and the raw materials used by the secondary and tertiary producers. Rice and these primary producers undertake energy conversion and storage in a similar manner. They absorb a large amount of solar energy, carbon dioxide, and nutrients from water and soil to manufacture organic matter by photosynthesis, and they convert, transport, and store energy. When rice looses nutrients because of competition among the biological communities, this degrades the growing environment and increases factors that are unfavourable to growth. Weeds and large losses of bacteria and plankton through water movement waste nutrients and solar energy.

However, if fish, especially herbivorous and omnivorous fish, are introduced into the ricefields, they add a new link to the food chain. They feed on the primary producers and therefore reduce energy losses and improve the use of photosynthetic products. Fish culture yields products, which can be consumed by humans, and promotes transformations in the ricefield ecosystem that increase the carrying capacity of the ricefield. Rice-fish mutualism is the best way to maximize the output of the ecological system, improve its functions, and reduce the loss of materials and energy. It is one of the most important natural ecosystems.

Mutualism of Rice and Fish

In the rice-fish ecosystem, rice and fish play the lead roles. Some of their ecological requirements are similar and this provides the basis for their synchronized growth. Fish are poikilothermic aquatic animals; rice plants are thermophilic and semiaquatic. Although each grows and multiplies in its own way, they have identical characteristics in relation to water. Water is a prerequisite for raising fish and is also important for the growth and development of rice. Water, as a component of plant cytoplasm, is indispensable for the synthesis of organic matter in plants and for the absorption and transfer of nutrients. Water is also a raw material in many metabolic processes. The amount and quality of water are also key factors in the survival and growth of fish. Both rice and fish need water. That is their common characteristic.

The relations between water, rice, and fish must be handled correctly by controlling water (through ditches or outlets), while satisfying the water needs of different growth stages of rice (proper irrigation and water discharge). Rice needs water about 2.5-cm deep during the nursing stage, about 5-cm deep in the booting and earing stages, and about 6-cm deep in the milk and dough stages. Fish, especially grass carp, which are adaptable to shallow waters, needs the same depth of water as rice. Therefore, it is possible to balance the water supply for both rice and fish by digging ditches or pits.

Because rice and fish also grow in the same temperature range, they can be grown in a synchronized manner. For example, temperatures above 10°C are suitable for the growing period of rice, temperatures above 15°C suit the active growing period, and 21-25°C is the optimum temperature for rice, especially during the ripening period. If the daily average temperature is lower than 11°C and lasts for three consecutive days in spring, early rice may rot. If the temperature in May is low, if there is a cold moist wind in autumn, or if the daily mean temperature is lower than 20°C, tillering of early rice and booting of late rice may be affected. If the daily mean temperature in summer exceeds 30°C and the highest temperature exceeds 35°C, the earing of middle rice may be harmed and ripening may be premature. Hybrid late rice is seedless if the temperature is above 38°C for five consecutive days. The optimum temperature range for common carp and crucian carp is 14-18°C; the range for grass carp, silver carp, and Beijing bream is 18-20°C. The temperature range 26-32°C is the peak feeding period. When the temperature goes over 38°C or drops to below 11°C, fish loose their appetite. When the temperature drops to about 4°C, fish go into a dormant state, although they can still survive. The optimum temperature for the tropical nile tilapia is 27-28°C and its critical temperature for survival is 10-38°C. Growth is inhibited when the temperature reaches 38°C, and temperatures below 10°C are lethal for tilapia.

Ecoagriculture

Ecoagriculture should not be assessed only in terms of grain output; quality, total biological output, and profits should also be considered. A highly efficient and rational agricultural ecosystem is ecologically balanced. There should be a balance between tilling and nursing and between input and output. There should also be unity in economic and ecological objectives.

In the artificial rice-fish mutualistic ecosystem, green plants are the primary producers that convert solar energy into the food energy the fish require for their survival. The sequential relationship in the distribution of rice and fish is apparent. A study of the ecology of fish in ricefields shows that fish feed on plankton (that compete with rice for fertilizer), insects and bacteria (that harm rice plants), and mosquito larvae (that are harmful to humans). Fish assimilate only 3% of these feeds and discharge the rest into the ricefield. When they swim in the water, fish release carbon dioxide and this increases the amount of carbon available to the plants. They also break the soil surface and oxidize layers of soil, which increases the supply of oxygen and promotes root growth.

Rice-fish culture increases the output of rice by more than 10% (range 8-47%). It is necessary to establish that rice is most important in rice-fish ecoagriculture to fully exploit its benefits, avoid harmful effects, and strive for maximum output using the least possible energy and materials. Recent improvements in rice strains and crop systems have produced great advances in rice-fish technology. For example, the raising of grass carp fry in late ricefields can yield 150 000 fry/ha in about 25 days, while improving the fertility of the field.

The new technique of combining ditches and small ponds in ricefields raises the temperature of the mud and water and aerates the soil. The technique may help improve cold water low-yielding fields shadowed by hills and prevent drought in fields on the sunny side of the hill. A rational layout of ditches and small pools also reduces the concentration of mosquitoes in the centre of the field, which reduces the number of mosquito larvae and improves health conditions in rural areas.

Grass carp raised in double-cropping fields not only eliminate some pests of rice, they also feed on and digest the nucleus of the bacteria that causes sheath and culm blight. Fish excrement does not inhibit the growth of the bacteria’s nucleus, but it does retard the growth and activity of the cell walls of the bacteria. Grass carp may be an effective way to prevent sheath and culm blight from spreading in ricefields.

High ridges and low furrows turn horizontal production into vertical development. This helps improve the gley horizon of ricefield soil and expands the ploughed zone, which, in turn, promotes the growth of plants in the border rows and stimulates the development of individual rice plants. These developments lead to economic benefits. Yields of 15 000 kg of rice and 1500 kg of fish per hectare can be attained. The latest scientific research should be applied to further improve rice-fish culture techniques and increase production.

New techniques maximize the use of ricefields by combining rice-fish culture with soil and farmland improvement and environmental protection and by adapting rice-fish culture to local conditions. The techniques include: planting rice on ridges and raising fish in furrows in low-lying land, in water-logged ricefields with a gley horizon, in cold-water fields, and in ricefields near mines; and digging ditches and small pools in dry, hilly ricefields. In fields where yields are stable despite drought and waterlogging, farmers should adopt methods such as intercropping, crop rotation, and the use of the free period during late rice, to increase biological control of rice pests and the yields of grass carp fry. Operations should be diversified by growing rice with azolla and fish or by growing rice with fish and frogs. These options will enhance the fertility of the fields, expand production, and improve economic results.

Forms of Rice-Fish Culture

Hunan Province is south of the middle reaches of the Yangtze River (24°30’-30°08’ N). The influence of the monsoon is strong, and there are four distinct seasons. Hunan has a subtropical humid monsoon climate and an annual mean temperature of 16-19°C. The lowest temperature suitable for rice and fish growth spans more than 8 months. There are 270-310 frost-free days, 1300-1800 h of mean solar duration, about 3 months of rain, and 1200-1800 mm of annual precipitation. Light, heat, and water are concentrated in April-September each year.

The principal crop in the province is rice, which is grown on 2.8 million ha. High- and intermediate-yielding fields make up 64.7% of the total area. Single-crop rice (one middle rice or a late rice) is grown on 0.5 million ha, mostly in the western and southern parts of the province. Based on the distribution of ricefields in the area, the available resources of light, water, and heat, the current production of rice and fish, and technical conditions, rice-fish culture can be developed in four different areas in Hunan.

Western Hunan

The area covers the Western Hunan Autonomous Prefecture, the Huaihua Prefecture, Cili, Taoyuan, and other hilly counties with high altitudes and terraced and sloping land that lacks the ability to conserve water and fertility and to resist drought. The southwestern part of the area is warm; the north is cool, humid, and foggy. Annual mean temperature is 15.8-16.8°C, 1-3 degrees lower than in other areas of the province. Annual solar duration is 1300-1500 h, which is less than in northern Hunan. Annual precipitation is 1300-1500 mm, one of the lowest in the province, but with 330-550 mm of rain in July-September, it has the wettest summers.

Ricefields take up a large portion of the arable land; most ricefields are hill-shadow fields, cold-water fields, and winter-ponding fields. The time for raising fish is long. Because there are few ponds and reservoirs, the area depends mainly on rice-fish culture for its supply of fish. The area has a long history of rice-fish farming. In the past, people raised mainly common carp by collecting locally available fish eggs and hatching them. These operations were extensive and the variety of fish was limited; therefore, catch per unit was low.

Fish production in ricefields could be increased by improving production conditions in middle ricefields, adding irrigation facilities and fertilizer, improving fish-raising techniques, and developing more varieties of fish. Fry should be hatched outside the fields, seeded in summer, and raised in small ponds in or outside the ricefields. Farmers should also be encouraged to seed bigger fry, mostly common carp mixed with some grass carp, crucian carp, and tilapia.

Southern Hunan

The area covers Hengyang City and Chengzhou and Lingling Prefectures. It has an abundant supply of heat and leads the province in degree days, with 5300-5600°C and an average daily mean temperature of 10°C. The annual mean temperature is 17.5-18°C, the lowest average temperature is 14°C in March, and the mean temperature in mid-October is 16.5-19°C. Annual precipitation is 1300-1500 mm, with about 200 mm falling in July-September. The rainy season ends in July, 10-15 days earlier than other areas of the province.

Conditions are favourable for rice-fish farming, especially in spring. The area has abundant sunlight, an annual solar duration of 1600 h, and 193-195 days with temperatures above 15°C. This provides ample time for fish growth and encouraging results have been obtained with fish raised in winter-ponding fields.

The soil in the ricefields is mostly fertile tidal sand mud and black river mud. Historically, the area practices double-cropping. (The double-cropping system of planting soybean with hybrid rice in spring was recently introduced and proved to be a great success.) However, low-yielding fields account for a third of the total ricefields, and there are also some gley horizon ricefields in valleys and lowlands where the soil particles are dispersed and marshy. A soil-amelioration plan should be developed to transform the soil by opening up drainage ditches and flood diversion channels and canals to direct mountain floods and toxic wastewaters from mines away from the fields and underground water. Cold run-off water and water high in iron content should also be drained from the fields. Low-yielding ricefields could be improved if fish were raised in combination with the rice.

In the Hengyang Basin, fish culture in ponds and pools is flourishing and is well-known throughout the province. There are ample sources of fish fry and many fish varieties. Local people collect fish fry along the Xiangjiang River and raise the fry themselves. To take advantage of favourable conditions, the culture of diverse varieties of fish in ricefields should be encouraged. At the same time, fish culture in ponds should be continued. The terrain and weather conditions are variable, which is favourable for raising fish. A variety of rice-fish culture techniques, including fish-seedling-rice, rice-seedling-fish, seedling-rice-fish, fish-rice-seedling, and fish-rice-fish should be adopted.

In the immediate future, more grass carp varieties should be cultivated in the wheat-rice fields to ensure the supply of fry for intensive pond culture. Fish production, from egg collection to the culture of adult fish, should be streamlined by combining the practice of fish-raising in small pools with rice-fish culture, and by combining rice-fish farming with pond culture. To expand the area of surface water and to produce fry on a commercial scale, it will be important to cultivate fry in ricefields.

In areas where farmers grow early ripening varieties of late rice and plant grass to raise common carp, the area for rice-fish culture should be expanded by raising mainly common carp and some other varieties. In winter-ponding fields where fish are raised, more feed and fertilizer should be applied and a mixture of species should be used to develop intensive fish culture within one season. In Ningyuan, Jiangyong, Daoxian, and Lanshan where tilapia can over-winter, fish varieties should be improved and more nile tilapia should be raised.

Central and Eastern Hunan

The area covers Pingjiang, Liuyang, Changsha, Wangcheng, Ningxiang, Chaling, Youxian, Liling, Junxian, Xiangtan, Shuangfeng, Lianyuan, Xinhua, Xinshao, Shaodong, Shaoyang, Longhui, Dongkou, Wugang, Suining, Chengbu, and Anhua. Water and heat are abundant and increase gradually from the northwest to the southeast. Annual solar duration is 1500-1740 h. Precipitation in the Dongting Lake area alone is 1300-1500 mm annually, and 170-190 mm fall in August-September. The lowest rainfall is in autumn. Most of the ricefields are distributed between hills and the soil is a red clay. The main cropping system is double rice plus green manure. Most of the counties in the area raise fish in ponds and reservoirs.

The area should raise more fish, both fry and adult fish, in ricefields and continue pond and reservoir culture. Grass carp should be raised in late ricefields and tilapia should be grown where there are geothermal resources. In areas where rice-fish farming is practiced, farmers should be encouraged to seed bigger fry, raise adult fish, and expand the area devoted to rice-fish cultivation. At the same time, efforts should be made to popularize and improve fish-raising techniques.

Lakeside Rice-Fish Culture Area

The area covers Huarong, Nanxian, Anxiang, Lixian, Changde, Hanshou, Yuanjiang, Yiyang, Xiangyin, Miluo, Linxiang, Yueyang City (county), Jinshi, and provincial farms and fish farms. With its alluvial plains, abundant water resources, and fertile soil, this area is the centre for commodity grain production. Double rice crops are grown on 92% of the land and green manure on 80%. There is plenty of gley horizon soil. In some open expanses or plains, surface water often accumulates and a layer of green mud appears near the plow base. In some places, the soil is submerged in water all year round, and the soil particles are dispersed, muddy, and marshy.

There are vast expanses of water that are often interconnected. The area is one of the most important ten freshwater fish areas in China. There are about 170 000 ha of exploitable water surface in the area (50% of the provincial total), but fry are in short supply.

Weather conditions are good, with abundant sunshine and heat, but less rainfall. Spring comes late and autumn sets in early. Solar duration is 1700-1800 h annually, the longest in the province. Annual mean temperature is 16.3-17°C and annual precipitation is 1200-1500 mm. Precipitation is concentrated in April-September, which account for about 800-1000 mm (67% of the annual total). Because summer is late, early rice often ceases to sprout because of low temperatures in May. The first day when the daily mean temperature is 12°C about 5 April, and the last day when the mean temperature is 20°C is about 25 September.

To match the mode of production to the lakeside ecology and economic conditions, the area should concentrate on improving the soil, transforming low-yielding land, and raising fish in ricefields by introducing the method of growing rice on ridges and raising fish in furrows. At the same time, efforts are needed to develop sources of grass carp fry. Technically, several points require attention:

· Breeding and selection should be intensified to advance the artificial breeding of grass carp to the end of April to match the seasons for rice and fish production. This would overcome the need to keep rice in the field to let the fish grow and would improve land use.

· Methods of raising fish in both ponds and ricefields and of hatching fry outside the fields should be introduced. This would mean that fry could be seeded before the early rice seedlings begin to turn green, and the fish would have enough time to grow and eat weeds.

· It is advisable to raise fish in ricefields with plain open areas and good drainage and irrigation systems. Flood-diversion ditches, water-directing canals, and round-the-field drainage ditches are needed to prevent floods and waterlogging and to prevent fish from escaping with the irrigation water.

· To stimulate rice production by raising fish, fertilizer should be properly applied in gley horizon ricefields. More phosphate and potash fertilizer should be applied according to the characteristics of the soil to improve the quality of crop cultivation. Muddy fields should be plowed less and extensively worked. Ridge culture should be adopted in marshy fields to breed strong, sturdy seedlings. Resistant rice varieties should be planted to increase output.

· In water-logged areas in which rice output is low, the soil should be dug deeply, ridges should be built, and fish should be raised in ditches and pools. Mulberry trees and hemp can be planted on the banks. Sericulture can be undertaken, silkworm excrement fed to the fish, and fish dung used to fertilize the soil. The mud from the pools or ditches can be used to fertilize the soil in which the mulberry and hemp are grown, and the hemp leaves can help preserve water. The cycle provides economic and ecological benefits.

Yang Jintong is with the Aquatic Production Technology Station, Changsha, Hunan Province.

Value of the Rice-Fish Production in High-Yielding Areas of Yuyao City, Zhejiang Province

Cao Zenghao

In Yuyao City, Zhejiang Province, rice-fish farming was developed in the 1950s at scientific institutions, state farms, and some fishery villages. However, because of changes in production relations and farming systems, rice-fish farming soon stagnated. In 1978, it was revived.

Experience has shown that integrated rice-fish production offers economic, social, and ecological benefits. It has become an important way to increase the income of grain-producing households, diversify single-product economies in rural areas, and supply animal protein to improve the nutrition of the people. There are new problems. Rice-fish farming is limited in high-yielding ricefields where labour is limited, where arable land is limited and highly productive, where there are a large number of households that work the land part-time, and where township enterprises are well-developed. However, these contradictions can be mitigated by research and field trials to develop rice-fish farming techniques to produce high yields of rice and fish.

Benefits of Rice-Fish Culture

Recent multilocation trials, demonstrations, and extension efforts in Yuyao City have shown that major benefits can be derived from integrated rice-fish production systems.

Efficient Use of Natural Resources

Yuyao City in the southeast coast (29.39°N, 120°E) has an accumulated temperature of 5073°C, 210 frost-free days, and abundant precipitation and sunlight. It is a high-yielding area that produces a double crop of rice (10-11 tonnes/ha of early and late rice). These temperature, sunlight, and meteorological conditions are also suited to fish culture. In a 1986 study of 107 lowland rice-farming households in Changlou township, fish were cultured in 21.1 ha of ricefields. The output was 6400 kg/ha of early rice and 5260 kg/ha of late rice, which was the same output produced in ricefields without fish culture. Adult fish were cultured in 6 ha with an output of 926 kg/ha. Production reached 11 250 kg of rice and 750 kg of fish per hectare, and the value of the output was doubled. Another 15.1 ha were used to produce 499 kg of fingerlings per hectare.

Farmer Yang Tiexian dug ditches in 11% of his 0.18-ha ricefield to breed 120 grass carp, 1000 bream, 750 crucian carp, and 5000 adult carp in early spring. By 10-15 October, he harvested 703 kg (3905 kg/ha) of rice and 100 kg (558 kg/ha) of fish. His experiments were verified by researchers from both Ningbo and Yuyao.

This example illustrates that pits and ditches for fish culture can enhance the growing environment for both rice and fish and can increase economic efficiency. Organic matter in the water (e.g., plankton, benthos, insects, weeds, and organisms harmful to rice) serve as fish food. The movements of the fish stir the water and loosen the soil to improve oxygenation and soil fertility. Fish feces are quality organic manure for rice.

Intensification of Agriculture

Farmers in Yuyao City only have about 0.05 ha of ricefields each. The multiple-cropping index has reached 240% and the population continues to grow rapidly. The amount of arable land limits agricultural production. For this reason, agricultural production must be diversified and farming must be intensified to obtain maximum economic, social, and ecological benefits. Rice-fish farming is an effective way to increase productivity when farmland is limited.

Farmer Jin Wanshun and his family contracted 1 ha of ricefields. Since 1984, he has managed this farm using an integrated method that includes growing rice, fish, fruit, and vegetables. In 1987, he implemented the rice-fish system and planting grapes and vegetables on the ridges of 0.7 ha of ricefields. He harvested 12 335 kg/ha of rice and 1061 kg/ha of fish. His family sold 5200 kg of commodity grains, 440 kg of live fish, and 150 kg of fingerlings. Calculated on the basis of local prices, his family earned CNY 2514 from rice, CNY 3305 from fish, CNY 1000 from melons and vegetables, and CNY 4000 from household sideline products. Of the total income of CNY 10500, rice-fish farming contributed 30% to total income and 46% of agricultural income.

Integrated rice-fish production plays an important role in the development of a diversified economy. Its economic benefits are double those obtained in monoculture under the same conditions.

Creation of a Favourable Ecological Environment

At present, increased crop yields depend on the application of a large amount of fertilizer. These fertilizers have increased energy consumption and production costs and polluted the environment. In the rice-azolla-fish ecosystem, azolla is a fertilizer and food for the fish. Fish eat insects and weeds, and their feces fertilize the rice plants. This reduces the need to apply chemicals because pests and diseases are minimized and soil fertility is improved.

In Chang Feng Township in 1985, farmer Chen Bingcan and his family contracted 2.3 ha of farmland. They used the rice-fish system and grew rice with azolla in the spring and fish in the summer and autumn. After 3 years, soil fertility had greatly improved. The Institute of Soil and Fertilizer, Zhejiang Academy of Agricultural Sciences, determined that the organic matter content of the soil had increased from 2.9% to 3.3% and that the nitrogen content had risen from 0.2% to 0.3%. Pest damage was also reduced, and weeds had been reduced by 56 times. There were only 27 weeds/m2 in the ricefield with fish and 1521 weeds/m2 in the field without fish. Sheath blight had declined from 47% to 33%. Rice seedlings were transplanted into untilled ricefields, which meant that plowing and weeding were not necessary. The application of fertilizer and agricultural chemicals was reduced by 40%, which lowered production costs and increased income.

A 1987 survey showed that a 1.7-ha ricefield that used the rice-fish integrated production system yielded 2860 kg of hybrid rice seed, 1560 kg of rice grain, and 2860 kg of live fish. The income was CNY 6240/ha, or CNY 3820/ha more than the CNY 2420/ha that was obtained from planting rice alone in a 0.4-ha ricefield.

Limiting Factors

Although Yuyao City has favourable temperature, sufficient sunlight, and 2915 ha of ricefields for rice-fish farming, there are also limiting factors.

Scattered Plots and Extensive Cultivation

Since the implementation of the production responsibility system, most farmers have only have about 0.2-0.3 ha of arable land. Many have left their farms to work in township enterprises. The resulting labour shortage has limited the development of rice-fish production systems.

Limitation of Traditional Cropping Systems

There are contradictions between the management techniques for the traditional rice-cropping pattern and the rice-fish pattern. For example, when the close planting pattern (12.5 cm x 12.5 cm x 12.5 cm x 10 cm) is adopted for transplanted rice, toxic chemicals are applied to prevent pests and diseases and the field is frequently idle. These chemicals limit rice-fish farming.

Lack of Knowledge of Fish-Culture Techniques

Farmers are experienced in rice farming but lack knowledge about fish culture. Techniques for breeding fish in ricefields have been developed in recent years, but farmers need more technical guidance as well as an effective service system and administration. The supply of fish fry and fingerlings are insufficient. These factors have constrained the development of the rice-fish production system.

Future Needs

Identification of Development Priorities

To boost the commodity economy in the countryside and to improve its efficiency and benefits, arable land must be gradually centralized by big rice-grain producers in rural areas. This centralization should be followed by extension information about rice-fish production systems.

Strengthen Research

The rice-fish production system lacks a model and must be standardized to be easily adopted by farmers in rice-growing areas. Rice-fish farming techniques should be disseminated through technical training, demonstrations, and on-farm visits.

Improve Engineering Facilities

Rice-fish farming facilities must be altered to enhance the symbiotic environment. Scattered and shallow trenches should be converted to centralized and deep trenches that make up 6-8% of the total area of the ricefield. The growth of both rice and fish should be promoted by providing a habitat for fish migration and by changing from square close planting to wide-row close planting. These changes will alleviate the contradictions between fertilizer application, water irrigation, plowing, transplanting, and pest control.

Enhance Cooperation and Service

The rice-fish integrated production system is multidisciplinary and combines agronomy with the aquatic products industry. To develop fish farming in ricefields, farmers must be provided with an adequate supply of fish fry and fingerlings, marketing information, and an effective fishery administration to ensure production safety.

Cao Zenghao is with the Yuyao Aquatic Product Bureau, Yuyao City, Zhejiang Province.

A Comparative Study of the Ability of Fish to Catch Mosquito Larva

Wang Jianguo and Ni Dashu

More than 100 species of fish eat mosquito larva, and many authors have suggested species that are good at eating mosquito larva. In 1959, Chen Jiangxing and Gao Kai achieved good results using common carp fry (Cyprinus carpio), and in 1979, the Antiepidemic Station of Chengdu City, Sichuan Province, used silver crucian carp (Carassius auratus) and grass carp (Ctenopharyngodon idella) to eliminate mosquito larva. In 1976, the Antimalaria Group of Henan Province reported good results when fish were raised in ricefields to control mosquitoes. Although Dambusia affinis, Panchax panchax, Mocropodes apercularis, and Pseudorasbora parva are good for mosquito control, they are difficult to breed and there is a limited supply of fry. In addition, these fish species are of little economic value and are difficult to popularize.

There have been no reports on the ability of such fish as grass carp, silver common carp (first generation of crosses between red carp and silver crucian carp), and nile tilapia (Oreochromis niloticus) to eat mosquito larva. Earlier indoor experiments reported by the World Health Organization were mostly conducted with fish that were starved for 1-2 days before the mosquito larva were introduced.

A comparative experiment was carried out to determine the differences between the amount of food taken by starved fish and by those reared in natural conditions. Three common types of fish raised in ricefields were studied. The density of mosquito larva in one midseason ricefield and two late ricefields where grass carp were reared was also measured.

Materials and Methods

The research was conducted both indoors and in the field. The experiment on the feeding rate was done indoors under controlled conditions. Fish of different sizes were raised separately in a white round drum (40 cm in diameter, 20 cm of water). To test the food intake of hungry fish, the fish was starved for 24 h after they had adapted to their new environment. To test the food intake of fish under natural conditions, the feed most liked by fish was added after the fish had adapted to their new environment. Mosquito larva were added in batches. The amount of feed added or unconsumed, and the number of mosquito larva of different ages eaten by the fish, were recorded.

The survey of the density of mosquito larva in ricefields with and without fish was carried out by collecting water samples with a 500 ml aluminium ladle. If water depth in the ricefields is assumed to be 6 cm, every hectare of ricefield stores 600 m3 of water, which is equal to 1 200 000 of the ladles used to collect samples. A sample consisted of 150 ladles of water collected along the banks of a field. The mosquito larva were separated from the water using a glass pipette and fixed in a bakelite-capped tube that contained 30% alcohol. The larva were counted according to three categories: Anopheles sinensis, Culex spp., and others. Between July and August 1984, four samples were collected once every 2 weeks from the middle ricefield. In 1985, the survey on a large area of two seasons of late rice was conducted.

The survey of the mosquito larva density in the middle ricefield was conducted in the Lianhu Fish Farm, Mianyang County, Hubei Province. The farm had 57.7 ha of intensive fish-farming ponds and 31.7 ha of ricefields in continuous blocks. The ricefields were surrounded by 1.6 ha of ditches. The ricefields were divided into four blocks and managed by four different fish-farming teams. The area of the four blocks of ricefields was 1.8 ha and the three fields were about 7.8 ha each. The adjacent 5.3 ha of ricefields in which fish were not raised were used as the control field. The strains of rice in the fields were different, but all were middle rice (the distance between rows and plants was 13 cm x 20 cm). Tillage was not done in ricefields in which fish were raised. No fertilizer was applied, and pesticides were used only when necessary.

On 18 April 1984, sodium pentachlorophenate was used to eliminate weed, fish, and leeches from the ricefields, and fry were raised in the 0.8 ha of straight ditches around the four blocks of ricefields. On 19 May, 1.1 million grass carp fry were introduced. On 23 June, 2.6 million summer grass carp fingerlings were collected. In late June, 390 000 summer grass carp fingerling and 30 000 silver crucian carp fingerlings were released into the rice paddies (average 13 230/ha or 1-2/m²). In ricefields with fish, fish ditches were dug. No feed was put into the ricefields. The surveys of the density of mosquito larva in the two seasons of late rice where grass carp was raised and in the control fields were conducted on 10 ha in Chongyang County, Hubei Province.

Results

The food intake of hungry fish and fish under natural conditions were quite different. The number of mosquito larva eaten by grass carp under natural conditions was 73.4% of the intake when the fish were hungry (Table 1). Silver crucian carp consumed 36.3% under natural conditions compared with hungry conditions (Table 2). The number of mosquito larva consumed by nile tilapia under natural conditions was only 32.5% of that under hungry conditions (Table 3). Nile tilapia showed the greatest differences in intake under the two conditions, followed by silver crucian carp and grass carp. In the indoor experiment, grass carp almost always preferred mosquito larva to duckweed when they were fed together. This may explain why grass carp normally eat more mosquito larva than the other two species. Tables 2 and 3 show that when feed is given, the silver crucian carp and nile tilapia eat more fish powder than mosquito larva. The intake of mosquito larva is not correlated with increased body size (Tables 1-3). In both groups, grass carp eat the greatest number of mosquito larva, followed by silver crucian carp and nile tilapia.

The number of Culex spp. larvae consumed can be determined by counting the respiratory ducts that survive digestion intact. During the experiment, of the 300 Culex larva fed to the fish, only 261 respiratory ducts were recovered (253 from fish excrement and 8 from the sediment). This is only 87% of the number consumed. This suggests that when the number of mosquito larva consumed by fish is assessed, the number should be corrected by 13%.

The field surveys of the middle ricefields in Mianyang County (Table 4) show an average of 32 000 larvae when no fish were present, and one-third of that number when fish were present. The fields without fish had four times the number of Anopheles sinensis and five times the number of Culex spp., but the same number of other mosquito larvae. In a more extensive survey in Chongyang County (Table 5), the fields with grass carp had 900 larvae per hectare compared with 66 700 in the fields without fish (a difference of 99%). In this area, only one field with fish had any mosquito larva. This field monitoring clearly shows that grass carp can eliminate large numbers of mosquito larvae from ricefields.

Discussion

Grass carp more effectively eliminate weeds and mosquito vectors in the ricefield than silver crucian carp and nile tilapia. Their body shape also seems to be better adapted to the shallow water in ricefields. Grass carp also have a higher economic return. When the excrement of grass carp that have eaten mosquito larva was examined, only the respiratory ducts were found entirely intact. Although the head of the mosquito larva is shell-like, it was ground to pieces and could not be counted. However, Anopheles spp. do not have respiratory ducts and this method of computation requires further discussion.

According to a report by Yi Mengjie and his colleagues in 1984, a 4.9-cm grass carp can catch 141 mosquito larva per night. In our experiments, each night grass carp the same size could catch 236 mosquito larva, which weighed 8.3 g (100 II-IV stage larva weighed 3.5 g).

Generally, the peak period for mosquito larva in ricefields is between late August and early September. Because of the field work needed for watering and harvesting, our survey continued only until late August when there was no peak and mosquito density was not high.

Summary

There are differences among the three species of fish in their food intake. The number of mosquito larva eaten under normal conditions is lower than when the fish are hungry. When the fish are the same size, grass carp eat the most larva, followed by silver crucian carp and nile tilapia. Fish reared in ricefields can eliminate up to 99% of the mosquito larva, Based on the indoor experiments, 100% of the mosquito larva in the ricefield could be eaten and this would still not fully satisfy the food requirements of the fish. Based on our experiments, grass carp would be the best species to control mosquitoes in ricefields.

Wang Jianguo and Ni Dashu are with the Institute of Hydrobiology, Academia Sinica, Wuhan, Hubei Province.