Rice fish culture is an age-old practice and one of integrated bio systems in China. It went through a long process of normal development, severe fluctuation and rapid development. It shows its vitality in 1990s. Rice fish farming systems are now becoming rice aquaculture farming systems, developing from protein crops to cash crops. The paper describes present status and techniques by a case study and summarizes Chinese experience on developing rice aquaculture farming systems. The sustainable development of rice fish culture has its social, economic, cultural factors and radically, the philosophic concept of the Chinese people as well. 
 
INTRODUCTION 

Rice-fish culture means raising aquatic animals in irrigated rice fields to obtain aquatic products in addition to rice production, which is the main activity. Rice fish farming system with simple catch method is a capture system, which is not rice-fish culture system in deed. 

Only 0.65% or 136,000 ha of the total area of 21 million ha of irrigated rice fields in South East Asia are used for culturing fish (Coche, 1967). In countries with highly developed rice cultivation, aquaculture in rice fields is declining, especially in Asia and Europe. It is due to the introduction of high-yielding and short-stem rice varieties calling for a thin water sheet and use of agricultural chemicals which are toxic to water animals (Vincke J.C. Micha 1985). The most striking case of declination is in Japan. The production of common carp in rice-fish culture dropped from 4,400 tons in 1943 to 250 tons in 1963 (Fig. 1). Nowadays, no carp are harvested in Japan’s rice fields (Suzuki, 1979). The decline was mainly due to the advanced agrarian practices such as spraying of pesticides, herbicides and fungicides with high yielding varieties of rice. Multiple cropping does not provide long spells of wet fallow periods for fish culture (Baharin et al., 1979). Veravat Hongskul (1997) says higher education and rapid economic development had resulted in the young generation to shun away from fisheries. Like in Japan, the young generation avoids fisheries because of its 3K nature: Kitsui (hard work) Kitanai (dirty work) & Kiken (dangerous work). It seems to me that the main reason is its low comparative economic benefit. 

One of traditional integrated farming systems in China is rice-fish culture. Rice is the major staple food while fish is the cheapest animal protein for most of the world’s population. In China, a good place is often called Jiangnan, which means the place of fish and rice and literally means the area on the southern bank of the Yangtze River. Fish requires water and rice fields can offer water for fish in certain period of time, why not, then fish are cultured with rice? 

Rice-fish culture shows its vitality especially in China after its declination during Green Revolution. Chinese farmers solved the constraints of agriculture chemicals and sun drying in rice-fish culture in 1970s. It proves sustainable and so it is an important part of sustainable agriculture. 

China is striving to develop its fishery industry to help feed its growing population. Even the country’s paddy fields will play their part-by becoming part time ‘ponds’ for commercial aquatic farming with fish being reared alongside newly planted rice. Over 6.7 million ha of rice fields can be used for rearing fish. In 1997 the area of rice-fish culture reached 1.67 million ha with the total fish production of 700,000 tons from rice fields. The growth rate of aquatic production in China registered an annual increase of 11.6% in the past two decades, with the output climbing to 29 million tons in 1997, accounting for a quarter the world total. The aquatic production of China has been on the top place in the world for 7 consecutive years. The figure is expected to surpass 32 million tons by 2000. Fish production from rice fields will contribute an indispensable part. 
 

Photo 1: Rice field showing broad trenchfor fish cultivation and  Azolla fern in the forefront of picture.

PRESENT STATUS  

Fish culture in rice fields is widespread in Southeast Asia where it was introduced from India about 1,500 years ago (P. Vinke & J.C. Micha, 1985). It may be and it may not be. 

Rice-fish culture is an age-old practice in China, but there are no accurate records when it actually started. But unearthed relics and some ancient books are enough to explain when and where it came from. These unearthed cultural relics not only indicate that rice-fish culture in China dates further back to the East Han Dynasty (25-220), but also fills an important gap in kinds in the history of rice-fish culture in China (See Li 1988, Li 92). In nearly 50 years from 1949, rice-fish culture went through the process of normal development, severe fluctuations, then to rapid development e.g. taking Sichuan Province to represent the status of the rice-fish culture areas because of its similar situation with other provinces (Fig. 2). However, in rather developed areas in China, rice fish culture declined like the world situation. 
 
Why does it revive its economic viability in 1990s? This involves sustainability. Sustainability has four properties as criteria for analysis: 
Economic property: a system, which can raise the income of people who want to live a better life. It should be profitable especially in establishment of market economy. 
Social property: a human society, which develops equitably with eradication of poverty. 
Ethical property: an ethical idea, which emphasizes the welfare both for the present generation and generations after with environment conscientiousness of the people. 
Natural property: a balanced ecology on earth with limited natural resources. 

I’d like to discuss the sustainable properties of rice-fish farming systems through a case study. 

1. Rice-fish farming systems from protein crops to cash crops  
To appreciate the present development of aquaculture production in a context of global sustainability, it may be useful to introduce the terms "protein crops" versus "cash crops" in order to signify a basic value orientation related to various methods of production. 

"Protein crop" is used when production aims at achieving as much animal protein as possible by using resources generated within the regional ecosystem to meet the protein needs of low- income population, mostly in the developing world. In contrast "cash crops" aims at high value products for distant markets to meet the demand of higher income groups, mostly in the developed world. Typically the farmed species chosen are high valued marine fish and shrimps. Production is capital intensive, and depends on input from outside the ecosystem of the producing area (Second International symposium on Sustainable Aquaculture 1997). 

Rice-fish culture was practiced in China to solve "Hard to get fish" problem, especially in mountainous areas. Since the socialist market economy policy has been adopted, not only fish but also some high-valued aquatic animals as cash products are reared in rice fields without much investment. Thus, rice-fish farming systems are now becoming rice aquaculture farming systems, developing from protein crops to cash crops. 

In September 1994, the National Rice-Fish (Crab) Culture on-the-spot meeting was held in Liaoning Province. Afterwards, permitted by the State Council, the Ministry of Agriculture (MA) issued "Notes about accelerating the development of rice-fish culture so as to promote the steady increase of grain production and to enhance the income of farmers." In general, the price of 1 kilo of fish is two times the price of 1 kilo of rice grain. The price of 1 kilo shrimp 20 times the price of 1 kilo rice and the price of 1 kilo river crabs 50 times the price of 1 kilo rice grain. You can compare the crab prices: 20 yuan/kg in 1985; 40 yuan/kilo in 1991; 130 yuan/kilo in late 1992; 200 yuan/kilo in 1993 and then, the price dropped down afterwards. 

According to the MA the area of rice-fish culture would increase 5 million mu (0.33 million ha) each year in China and up to 2000, it will reach 50 million mu (3.3 million ha) with an output value increment of 50 billion yuan. Rice-fish area will reach 50% of rice fields suitable for it in China. 

2. Case study of Jiangsu Province  
Jiangsu province has more than 30 million mu rice fields, among which one third are suitable for rice-fish culture. The action plan was expressed in a joint suggestion to the provincial government from Provincial Agricultural and Forestry Bureau and Provincial Aquatic Products Bureau. The Extension Project of Large-scale, High-yielding, High-effective Techniques of Rice/Aquaculture in Jiangsu Province (1995-1997): 

Undertakers: The project was jointly undertaken and implemented by extension stations of aquatic product techniques in 56 counties or cities in the province. 

Objectives: to develop rice/aquaculture combined with reforming and ameliorating low-yielding paddies, ponds and waterlogging farmland for the purpose of increasing food production and income, promoting rural economy, and enriching farmers. 

Main targets: The area of rice/aquaculture farming systems 200,000 mu in 1995, 400,000 mu in 1996 and 600,000 mu in 1997. The unit rice output should be 400 kg/mu (6000 kg/ha) on average; the unit aquatic product output 40 kg/mu; the unit output of crab or shrimp 20 kg/mu; fish 50 kg/mu and the unit profit 1,200 yuan on average. 

Results: Rice aquaculture area in Jiangsu Province reached 1,034,600 mu (68973 ha) in 1997 (Table 1). The area of rice-crab culture in Jiangsu Province reached 541,700 mu (36,113 ha), which accounted for 52.4% of the total area of rice-aquaculture. They harvested 1,6245,000 kg of commercial crabs with average unit production of 30 kg and average unit profit 1,600 yuan per mu, the highest production of 60 kg of commercial crabs and unit profit 4,000 yuan (Table 2 & Fig. 3) 

In 1997 the area of rice-shrimp culture reached 208,000 mu (13867 ha), which accounted for 20.1% of the total area of rice-aquaculture system. They harvested 5,712,200 kg of shrimp with average unit production 27.46 kg/mu and average unit profit 1,400 yuan (Fig. 4). 
 
In 1997 the unit profit of rice/aquaculture fields was 2.86 times mono rice cultivation in paddies. The economic return was remarkable. It increased the income of farmers and greatly raised their enthusiasm of rice/aquaculture practice. If a farmer manages 2/3 of a hectare, the annual income could reach 13,000-15,000 yuan. It becomes an important approach of getting richer in rural areas (Fig.5)  

3. Summaries of rice-aquaculture project in Jiangsu Province:  

The project proves that rice-aquaculture system is a good measure to be taken with economic, social and ecological benefits. Nowadays it is not as doing a business in a small way as farmers’ doggerel says Rearing fish in rice fields is not for earning money, but trading some fish for a little oil and salt. 

Rice-aquaculture system has the characteristics of low cost, quick effectiveness and better economic returns. It has been recognized as an additional source of food and/or income in rural areas. It can increase rice production by 10%-15%. In general it could produce 50 kg of fish per mu and farmers will increase their income of 1,000 yuan per mu. Single crop farming system can only achieve 200-300 yuan/mu esp. in low-yielding paddies. The farmers are losing their interest to cultivate rice in paddies in some developed areas. Rice/fish culture does not damage the basic structure of rice fields and aquaculture does not compete with crops for land. It not only increases rice production, but also harvests fish, shrimp or crab with economic benefit over 800 yuan/mu, the highest 2,000 yuan/mu. It will raise farmer’s enthusiasm for crop planting. Comprehensive utilization of rice field resources not only can increase the total amount of food production, but also raise the effective output of fields. So it’s in conformity with high quantity, good quality and high economic efficiency agriculture. It would enlarge collective economy and increase the income of farmers. 

It would promote agricultural scale-management and speed up agricultural modernization. Stretches of farmland were combined for the development of rice/aquaculture with scaled intensive management. There are 8 counties with 50,000 mu of rice/aquaculture and 20 towns with more than 5,000 mu of rice/aquaculture. The area of rice aquaculture systems in these counties reached 600,000 mu (40,000 ha), which accounted for 58.2% of the total rice-aquaculture fields in Jiangsu Province, promoting scale economy and raising socialized service levels. 

It develops ecological agriculture by virtue of the complementarity of respective superiority between crop planting and aquaculture. It promotes comprehensive utilization of rural resources and improves the rural environment. Rice-aquaculture farming systems could maintain ecological balance of rice field ecosystems. The rural environment can be improved, creating a favorable condition to develop non-pollution agriculture. The application of agricultural chemicals can be greatly reduced. Rice-fish culture also helps eliminate mosquito larva harmful to human health. 

Japanese encephalitis and malaria, these potentially fatal viral diseases transmitted by certain mosquitoes are found in a wide belt of Asia. Their prevention depends on improved environmental manipulation to stop the mosquito breeding in rice fields. The people use a vaccine but the cost is too high. Azolla, the floating water fern has been tried for mosquito control in rice fields. But it needs blanket coverage. The best way is to develop rice-fish (Birley, 1998). That’s true. Guangxi Institute for Prevention and Cure of Parasitic diseases conducted a 5 year investigations starting in 1983 on the effects of controlling mosquitoes after rearing fish in rice fields. They counted mosquito density in rice fields, frequency of mosquito biting and incidence of Malaria. The mosquito Anopheles sinensis is the main vector of local malaria, and Culex tritaeniorhynchus, the main vector of Japanese encephalitis in the district. One of the most important criteria for judging the control of mosquitoes is the incidence of disease spread by the mosquitoes. Table 5 shows the increased area of rice-fish fields in Quanzhou County and the annual incidence of endogenous malaria within the county and within the whole district. As the area of rice-fish culture increased in Quanzhou, the annual incidence of malaria decreased (correlation coefficient –0.9225) (Wu et al., 1988). 
 

TECHNIQUES  

Almost 97% of rice fields are irrigated in China. So we only discuss rice-fish culture in irrigated areas here. 

1. Classification of rice aquaculture farming systems  
From the viewpoint of production systems, they can be divided into the following: 

• Rotational rice-fish or fish culture in fallow seasons e.g. winter fallow in Sichuan; 
• Mixed rice-fish farming i.e., fish culture inter-cropping in one or two consecutive rice crops; 
• Rice-fish culture in both rotational rice fields and concurrent rice fields. 

Bedding pattern  
Ridging pattern so called semi-arid, free plowing pattern of rice tillage. The method is based on the principle of soil fertility bio-thermo-dynamics theory proposed by late Prof. Hou Guangjiong. From the viewpoint of targets of fish culture in rice fields, they can be divided into two: 
- Rice fields used as nursery to nurture fry to large-sized fingerlings 
- Rice fields used as grow-out pond to rear fingerlings to marketable fish. 
More than 50% of rice fields are used for grow-out. Generally speaking, fingerlings are raised in mixed farming system while commercial fish raised in rotational farming system or concurrent farming system. 
 
From the viewpoint of fish rearing patterns: 
Narrow ditch pattern is about 35 cm wide and 30-50 deep; high ridge and low ditches with 70-80 cm wide and 50-60 cm deep in a cross or double cross shape if the field shape is rectangular. The peripheral trench is 1.2 m wide and 80 –100 cm deep. Broad peripheral trench pattern is about 2-4 m wide and 1-2 m deep (15-20%). 
Trench + corner sump or central pond pattern, which is about 30-40 m2 in circular or square shape (8-10%) 

Earthwork and essential preparation for rice-aquaculture farming system 
Higher embankment, ditches or trenches, sumps, ponds or refuges, anti-escape walls, screens, and sluice gates are needed. The environment in rice fields is not as favorable to fish as that in ponds although the disadvantages can be solved by adequate facilities. In a chosen field, the bunds should be solidly constructed to a height of 66 cm to prevent escape of fish during heavy rain and to control burrowing by eels, water snakes and moles. Trench dimension is shown above. 

In general, rice production cycle includes shallow irrigation and sun-drying stages. In order to allow the normal activities of aquatic animals during the growing period trenches and sumps need to be provided. A fish sump can also provide a shelter for aquatic animals during the application of top dressing and insecticides and it is more convenient for harvesting if aquatic animals are concentrated in trenches and sumps. Recently sumps develop to ponds. Why? The reason is that it is easy to manage aquaculture in that way. Screens and sluice gates are essential to avoid escape of fish and other animals when rains pour. 

3. Selection of rice cultivar and aquatic animal species  

It is advisable to plant rice cultivar with strong stems. Rice should tolerate manure application. This is especially important if feeding and fertilization are adopted during rice-fish culture. In that case, the soil becomes very fertile and the rice tends to lodge. There is scanty information about rice cultivars in rice-fish fields. In a study case, they mentioned a new cultivar "Double large", which likes rather deep water and does not grow ineffective tillers. There is much room to be improved for plant breeders to breed a suitable cultivar for rice-fish culture. 
When selecting fish species and the stocking rate, the following conditions should be considered: availability of fry and fingerlings; herbivorous and omnivorous fish, which feed on the natural food in rice fields; tolerance to high water temperature and low night-time dissolved oxygen levels; short rearing period; and tame temperament. Most commonly used species are field common carp, common carp, grass carp, tilapia and catfish in China. According to the experience of farmers, black field common carp and tilapia are the best species for table fish culture because of their rapid growth. Grass carp and common carp are the ideal species for culturing fingerlings because their fingerlings are healthy and give high output. The survival rate of summer fingerlings is in general between 50% and 70% whereas the survival rate of fry is lower. From the economic point of view, stocking winter fingerlings is best because they can grow out to marketable size in the year. The stocking density in nursery and grow-out systems is shown in Table 4. 

Practice indicates that if common carp and tilapia are polycultured, common carp will gain more weight when tilapia digs the bottom. They can utilize different ecological niche, so to speak, to utilize different microorganisms. Fish diversity increased. High yields depend on the compatibility of those species. For the purpose of high yields, none except catfish Clarias gariepinus can play an important role, but its taste is not so good. If crossed with Chinese catfish C. fuscus, it is said that the hybrid tastes good. In addition Chinese cuisine would make the taste as good as mandarin fish Siniperca chuatsi in Lake Taihu. Catfish are omnivorous fish, resistant to diseases and are very adaptable to the environment of small water body with low dissolved oxygen. They are olfactory feeders and can bear prolonged exposure to extreme of turbidity as in rice fields. 

4. Rice-Crab culture  

Crab culture can be divided into 4 stages in Jiangsu Province: Stage 1, transient rearing of adult crabs in ponds from lakes; Stage 2, pond rearing of bred juvenile crabs; Stage 3, pen culture in lakes and Stage 4, rice-crab culture. Rice-crab culture occurred in 1992 and developed quickly in 1994. River crab or mitten-handed crab Eriocheir sinensis is famous by virtue of its mitten handed and delicious taste. It is an expensive item of food, relished especially for its ripe gonad. The nutritional content in 100 grams of edibles contains protein 14%, lipid 5.9%, carbohydrate 7%, moisture 71%, ash 1.8%, riboflavin 0.71 mg, Vitamin A IU 5960, 139 Kcal and some elements such as Ca, P, & Fe. 
 
River crabs adapt to different ecological environment. Its distribution is vast from Yanlu River in Liaoning Province in the north to Leizhou Peninsula in Guangdong Province in south China. The development of rice-crab culture has been an important measure to regulate rural industrial structure, to stabilize grain production and to increase income of farmers. If crabs are cultured with rice, rice fields offer abundant natural food and habitats for crabs while the excreta of crabs provides fertilizers for rice with mutual benefits in symbiosis. 
 
Hatching of the eggs has been successful in saline water either natural sea water or formulated saline water in China. The gist of rice-crab culture is as follows: 

Select fields near water source with quality water, clay substrate or better retention of water. A plot of rice fields with the area of 1 ha and one-crop a year is more suitable. Excavate peripheral trench 2-4 m wide, 0.8-1 m deep; cross ditches 0.8-1 m wide, 0.5-0.8 m deep and a sump with 20-60 m2 1 m deep as a nursery, a transient rearing pond or a harvesting pond. The aquaculture area accounts for 15-20% of the area under rice cultivation. Build anti-escape wall made of smooth materials such as plastic, glassy iron or corrugated sheet with a round corner. Screen inlet and outlet so as to avoid escape of crabs. 
 
 

Photo 2: Rice-Crab field with fence around the field.

Stocking size and density: Rice crab culture can be divided into nursery, grow-out and fattening systems. For nursery system, the stocking density is 0.3-0.5 kg of zoea/mu stocked from early May to early June. Zoea can be cultured to Stage V zoea (the size of 40-200 individual/kg) in 4 months. It could harvest 15-20 kg of button crabs per mu. For commercial grow-out system, the stocking density is 5-10 kg of button crab (40-100 individual/kg) or 4-8 kg of button crab (80-160 individual/kg) in one-crop rice fields. The stocking time is during Feb-March. If reared in wheat-rice rotational fields, the stocking time is in June. Button crab can reach the marketable size 125 g/individual. The unit production could reach 20-30 kg/mu. For fattening system, the stocking of juvenile crabs (50-100 g/individual) in batches is practiced from July for high density intensive fattening. Juvenile crabs can reach to marketable size at the end of the year. 

Feeds and feeding: The growth of crabs mainly depends on feeding artificial feeds except natural food --rotifers, Daphnia and water worms in rice fields. Feeds includes animal food (40%), such as trash fish, snail, clam, viscera of animals, blood meal and fish meal; vegetable food, which accounts for 25% such as vegetables, sweet potatoes, pumpkin, rice or wheat bran, leguminous cakes, and terrestrial grass or duck weeds, which accounts for 35%. In some places, pellet feed is used. The quantity of food for zoea rearing to button crab is 100-150% of body weight by 8-10 times a day. The quantity of food for juvenile crabs is 7-10% of body weight 4-6 times a day, reducing to 5% of body weight 3-4 times a day when they grow out. The feeding intensity of crabs depends on the temperature. The feeding peak is from July to Sept. The annual allotment of feeds is as follows: 30-35% for March to June; 65-70% from July to Oct. At the early stage of growth, animal feeds should be fine and steamed, feeding with small amount a time, and several times a day. During the middle stage of growth, vegetative feeds such as corn and wheat should be stewed plus pumpkin and sweet potatoes. During the late stage of growth, animal feeds are applied to satisfy the requirements of fattening and the development of gonads. Management is to control water quality, to apply basal manure and to control pests and diseases. Dissolved oxygen should be kept above 4 mg/l the whole year for crustaceans. Change a water layer about 20 cm every three days or 1/3 of water in a field every 10-15 days so as to make it clean. Apply basal manure usually long effective oil cakes before transplanting rice seedlings. Top dressing is to apply urea 5-6 kg once, 2-3 times a year. In order to prevent pests and diseases, 50-75 kg of quick lime are applied per mu 15-20 days before stocking to sterilize trenches thoroughly. Button crabs should be sterilized in a solution of malachite (0.2ppm). Lime solution should be sprayed to trenches and the sump in intervals after stocking. Agricultural chemicals are not used after stocking or low toxic, high effective chemicals are used. Pay attention to their concentrations and application method. 

Rice is often harvested around Frost’s Descent (18th solar term). Before reaping, crabs are concentrated to trenches by irrigating and draining for several times. Crab harvest is usually in October and November when their gonads are ripe, when west wind blows in China. Harvest depends on weather and marketing. If the temperature is higher or the price is not good, harvest could be postponed. But if the temperature drops fast, harvesting should be advanced to prevent crabs from burrowing into mud. It’ll be more difficult to harvest crabs. The method of harvesting is to collect crabs during their beaching habit at night or to use bottom trap net or draining the water. The catching rate could reach 95% above (Zhao Mingsen, 1994). 

5. Rice-shrimp culture  
About rice-shrimp Macrobrachium niponensis culture model, it has the same features: less investment, quick effective and good economic return. The gist of rice-shrimp culture is as follows: 
Excavate peripheral trench 4-6 m wide and 1.2-1.5 m deep, ditches and a corner sump or a transient pond like rice-crab culture. Screen inlet and outlet with small mesh size net cloth. 

Clean trench and sump with quick lime. Enrich water by applying farm manure. Transplant submerged plants such as eelgrass, stone-wort or pond weed. The coverage should reach 1/2-1/3 of water surface. 
Stock shrimp brooders into a cage in the sump for hatching and fattening in peripheral trench and ditches. The stocking density is 0.2-0.25 kg of brooders with 4-6 cm body length per mu whereas the stocking density of post larva is 15,000-20,000 /mu. For freshwater prawn M. rosenbergii, the stocking density is 2000 freshwater-acclimatized shrimp (1.5 cm sized) /mu. 

Feed soy bean milk and fish gruel to post larva at first, feeding 3 times a day. The daily ration is 20% of body weight. After 7-8 days, feed them pellet feeds or mixed feeds of wheat or rice bran with some animal food. Daily ration 10-15% of body weight. The protein content of feeds for M. rosenbergii is higher than river shrimp (35-40% at early post larva stage; 25-30% adult stage). 

Harvest in late November and December. Marketable size shrimp are taken out and sold while smaller ones are returned to the fields for further growth until next May or June for total harvest. For freshwater prawn M. rosenbergii, the harvesting should be in time according to air temperature. In all cases harvesting operation should take place as early as possible. 
 

DISCUSSIONS ON DEVELOPING RICE AQUACULTURE SYSTEMS 

Changes of ideas  

The development of rice fish culture reflects changes of ideas in agriculture. Over a long period of time agriculture is of single structure in China. The people often considered crop planting as agriculture. In this sense, agricultural structure only consisted of cereal crops and industrial crops (cotton and oil). In 30 years under the central planned economy, the concept of "grain was everything" dominated agriculture in China although the comprehensive development of planting, forestry, animal husbandry, side occupation and fisheries was encouraged. Therefore, rice fish culture was spontaneously practiced. The concept of "rice first, fish second" was imbedded in rice-fish culture. The people involved in agriculture did not attach the importance to aquaculture in rice fields. It reflects that food was not enough to fill the stomach of the people in that period. 

Late Prof. Nie Deshu had been engaged in renovations of rice fish culture since 1960s and sent a proposal to the central government in 1981. If the area of rice fish culture expanded to 100 million mu, increasing unit output 20 kg/mu on average, the total rice production would increase 2,000 million kg and also 30,000-50,000 million tail grass carp fingerlings (10-13 cm body length) could be harvested. This would provide large amounts of fingerlings for aquaculture. [Outlook Weekly (26)]. A rice field is like a small artificial open ecological system. The interaction between rice and fish was called Mutualism by Nie (1976) or "Waste not, want not" by Yin (1986), which indicates Chinese philosophy: the by-products or waste from one resource use must, wherever possible, become input into another resource use ---an ecological principle. Culturing aquatic animals in rice fields can reduce the loss of nutrients in fields. Fish and other animals will help control pests and will loosen the soil as a result of their swimming and food searching activities, thus, aerating the soil, enhancing the decomposition of organic matter and promoting the release of nutrients from the soil. The excreta of aquatic animals directly fertilize the water in rice fields. Primary production analysis indicates that the total fish production could be 13.9-33 kg/mu (208.7-504.2 kg/ha) only from the natural food from three trophic levels except rice plants in rice fields (Li & Pan 1992) (Table 3). 

The development of modern agriculture indicates that when the living standard of the people is raised, the food requirements of the consumers appear to be varied, especially on animal food, vegetables and fruit, etc. In order to meet the increasing demand of the people and sustainable development of agriculture, planting should be divided into three sectors: cereal crops, industrial crops and feed crops in structure, so called "nutritional element agriculture" (Huang Qinghe 1998). We must emphasize new concepts to optimize food structure and broader bio resources. We could ask for cereal crops, industrial crops and fodder crops not only from arable land, but also food from non-arable land, forests, mountainous areas, inland waters and oceans. 

Under the socialist market economy, there is no need to propose a slogan of "rice and fish, fifty-fifty". The farmers will do. The culture of low-valued fish is rapidly replaced by high-value species as farmers, logically enough, maximize their benefits by producing higher-priced aquatic products. Rice-fish farming systems are becoming rice-aquaculture systems. Single farming system is becoming a diversified part of macro-agriculture. 
. What is agriculture? The authoritative dictionary in Chinese says agriculture is a social production department, which uses living functions of plants and animals and gains various products through artificial cultivation and rearing. This is the traditional agriculture with 2-dimension production structure: plants and animals. It was the real situation of the past and present traditional agriculture in China. As is well known, bio resources on earth consist of plants, animals and microorganisms (bacteria, virus and fungus). Traditional agriculture should be changed to macro-agriculture with 3-dimension production structure: plants, animals and microorganisms. Microorganisms are small creatures, which can not be seen by naked eyes and easily be neglected. But microorganisms can also provide us food, fodder, industrial raw materials. Through microorganisms 50-60% wastes of plant and animal products can be converted to food, feed and industrial raw materials (Bao Jianzhong 1997). This means the traditional concept of "grain was everything" is now being replaced by modern nutrient food concept in agriculture. 
 
It is just in this background that rice-fish culture develops. Thus, the biotic aspect---autotrophs and heterotrophs and the abiotic aspect--- water, heat, light, air, nutrients and soil, time and space in rice fields can be fully utilized by living organisms and through microorganisms, part of the biomass on earth as input can be fully utilized as well. For example, by-products and wastes of rice fish culture can be further utilized as input to rice fields or other sectors, especially through non-green revolution by microorganisms (S T. Chang, 1998). That is the concept of ZERI. Mankind cannot expect the Earth to produce more. Mankind must do more with what the Earth produces (Pauli 1997). 

It is man’s social being that determines his thinking. A new concept comes from practice. The only criterion to be used in judging truth is practice. Then, our mind can change from linear thinking to spiral thinking. However, the new concept must be accepted not only by academic circles but also by policy-makers. Thus, it will be turned into an action plan, which will be beneficial to the people. 

Rice/aquaculture combines with the reformation of "Three low"  

The development of rice/aquaculture farming systems was in coincidence with structure regulation in aquaculture from commonly cultivated species to special aquatic products. Rice/aquaculture farming systems will optimize agricultural resources allotment, reform low-yielding farmland, low-yielding ponds and low-lying land. On the aspect of assorted production facilities, modern farmland and aquaculture engineering is built according to high standards. The problems concerning farmland, ditches, trenches, woods, roads, bridges, culverts, sluice gates, pumping stations and houses should be tackled in a comprehensive way in a certain area. Thus, it has improved the conditions of agricultural production and built high-yielding farmland. For example, in Jiangsu Province in 1997, there were 1,050,000 mu rice/aquaculture fields, among which 200,000 mu high-yielding farmland were reformed from undeveloped farmland and 800,000 mu fine farmland were ameliorated from low-yielding paddies. It combined with reformation of low-lying land from the beginning. It is in conformity with the ethical property of sustainability, beneficial to both present generation and generations after. 

3. Admin-Tech-Material combination  
"Admin" here means that the governments at all levels should strengthen the leadership. They should put rice/aquaculture system on the agenda of the governments and designate a special person to be responsible to it. They should put it into comprehensive programming of macro- agriculture to combine with agriculture resources development plan, amelioration plan of low-yielding farmland, water conservancy program, "grocery basket" program, and "eradication of poverty" program. "Tech" means technicians and extension personnel. Technicians and extension personnel should be encouraged to devote their knowledge to the development of rice-aquaculture systems. Uniform technical service is strengthened in many forms such as technical contract, tech consultation or technical economic entity. Contractors should be trained before. Demonstration should be conducted. Fisheries management must be strengthened to prevent pouching and robbery. 

"Material" means financial allotment of development fund from local government, loans from agricultural bank. The decision-makers should work out some most favorable policies to attract investment from rich families to develop rice aquaculture. "Material" also means seed and feed supply, etc. Uniform seed & feed supply, uniform water supply, uniform disease & pest control, and uniform purchase & sale should be practiced from the beginning. Availability of supplying fry and fingerlings is more important in developing rice-aquaculture. In early 1997, the Central Commission of Chinese Communist Youth League put forward an extension scenario of rice/fish techniques. They planned to enlarge four hatcheries, providing 2 million fry or fingerlings to poor households in 90 demonstration areas free of charge. They planned to train 1,500 rice/fish good hands across the country to help reach the goals: more than 500 kg rice/mu, 30 kg of fish/mu with an increase of income about 1,000 yuan per mu. 

As a matter of fact, the development of rice-aquaculture in China has its social, cultural, economic factors and radically the philosophic concept of the Chinese people as well. 
 

Photo 3. Rice field showing peripheral trench fof fish and cross ditches.

PROSPECTS 

Aquaculture in rice fields in the future  
China is a second-to-none country in inland fisheries but its fish consumption per capita was only 10 kg, less than the world average in 1980s. Although the fish consumption per capita is now over the world average in 1990s, it is still low. In order to boost inland fisheries, rice fields should and could be used for aquaculture. Aquaculture in rice fields is a new growth point in aquaculture.  It has the following features: increasing rice and fish production, raising cost effectiveness and economic returns and convenience to develop industrial management. So aquaculture in rice fields developed rapidly than ever. Rice-aquaculture is becoming one of ten practical agricultural techniques, which the Ministry of Agriculture plans to extend. Techniques of rice-aquaculture will become more sophisticated from bedding tillage pattern to ridging and ditching pattern and to broad trench plus corner sump or central pond. However, it will need more labor in this pattern. A machine will save labor for ridging and ditching pattern rice-fish. Earthwork is now being improved. It seems a standardized, horticultural and scientific rice-aquaculture ecological-system will be set up. Rice farming also can combine with duck raising or frog culture or mushroom culture in rice fields. This will further increase food security for the Chinese people. 

Surface aquaponics  
Growing terrestrial crops on floating beds on the surface of natural waters is a new method in China developed by Song Xiangfu in 1990. I called it surface aquaponics. It is different from aquaponics (Aquaculture + hydroponics) in the U.S.A. It could be adopted in ample eutrophicated inland waters e.g. ponds, pools, reservoirs and lakes. 

Special floating beds were used to serve as seedling beds and floating body. An ideal substrate was used for fixing seedlings and supplying moisture, carrying oxygen and nutrients to plants so as to guarantee the development of roots. An effective, slow releasing compound fertilizer was specially prepared to meet essential nutrient requirements for the normal growth of plants at initial stage. 

This project was originally based on the fact that the potential crisis of food shortage has been existing in China. As the population grows, the average arable land is decreasing. Spare arable land resources are rather scanty. This trend can not be reversed in the foreseeable future. Therefore, the full utilization of about 13 million ha surface of inland waters may be of immense value. 

During 1990-1996, 130 terrestrial crops including cereal crops, oil crops, vegetable and ornamental plants, belonging to 82 genera in 46 Families, were successfully cultivated on floating beds in five types of water bodies in Zhejiang Province, China. The accumulated trial areas reached 8 ha (Song et al 1997). Compared with crops in soil, crops on floating beds on waters have many advantages. Water logging and drought was avoided. Because of easy management, it saved a lot of labor and time. Crops grown on floating beds had higher and stable yields because of higher effective panicle rates, harvest index, 1,000 kernel weight and filled grain rate. The plant was also able to resist lodging and to offer quite fewer chances for the occurrence of plant disease and insect pests. Rice, wheat, barley and rye grass gained higher biomass. Afterwards, surface aquaponics is used to purify eutrophicated water. 

Preliminary test also indicated that terrestrial crop planting on floating beds could be integrated with fish culture, it could obtain higher yields of fish with fine quality than those without planting when the coverage of planting was below 20-30%. However, surface aquaponics should be further studied. Grass carp with the body length above 9 cm should be fenced out of planting area or they will feed on the roots of rice. But I think it is possible to solve the problem of effluents from fish- ponds. 

In recent years fish farmers turn their fish- ponds to rice paddies. Why? It is due to eutrophicated pond water. In the past the pond water depends on self-purification of natural waters e.g. lakes, but now the lake itself is eutrophicated too. Rice fields can be used to culture aquatic animals. Certainly, fish- ponds could be used to plant terrestrial crops on floating beds. 

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