Integration of fish culture with livestock and crop farming is an ancient practice in China. The concept of an 'all-round development of agriculture, animal husbandry, fisheries and other side-line occupations' widely adopted in modern China has resulted in different patterns of integration throughout the country. This is probably the most impressive aspect of Chinese aquaculture and of considerable value to other countries, particularly developing countries interested in integrated rural development.
The major species used in integrated fish farming in China are herbivores and omnivores, especially carps and tilapias. In some countries, experimental work is now underway to determine the possible use of the freshwater prawn Macrobrachium rosenbergii, but this is still in an early stage of development. In most cases the farmers in the region use a polyculture system. In China up to nine species are used, but elsewhere much fewer species and even monoculture of omnivorous tilapia is common. Even though it is generally believed that a polyculture system is more efficient in ponds receiving heavy organic manuring, it has yet to be established that the large number of species used are necessary or essential to maintain a balanced pond environment and to achieve the desired fish yield. The problems of raising enough fry and fingerlirigs of a large number of species, and indeed the consumer acceptance of some of them, may limit the development of this type of farming in some countries.
In China the animal commonly raised in association with fish ponds is the pig. The manure of pig is considered as important a product as the meat. Pigsties are often built on pond dikes to facilitate the application of manure, either directly or after fermentation. One pig is estimated to give about 3 500 kg of manure slurry. Empirical ratios of the number of pigs to be raised to pond area as adopted in China range from 15 to 45 pigs per ha, but the optimum ratios in relation to the capacity of the pond to mineralize the manure, under different temperature conditions have yet to be determined.
Other animals raised on integrated farms are ducks, cattle, sheep and chicken. It is estimated that 20 000 ducks produce 1 000 tons of manure per year and a cow 50 kg daily. It is reported that a Huzhou sheep produces enough manure each year to supply all the nitrogen, phosphorus and potassium needed for 1 mu1 of mulberry. This in turn not only feeds silkworms in the season but provides enough autumn leaves to feed a sheep all winter. Silkworms hatching from each sheet of eggs can produce 200 kg of excreta, sufficient to feed 25 kg of fish. In some of the Chinese farms all these animals are raised in accordance with the policy of diversified production. However, the economic efficiency of raising different animals and their role in integration may differ. Specific information in this regard will be necessary in making selection of animals for farming in other countries.
1 mu = 0.066 ha (1/15 ha) = 0.165 acres
The dikes and adjacent land in integrated farms are often used for growing fodder. The fodder is fed to the grass carp, but it is known that a part of the fodder is excreted undigested or partly digested and this also serves as manure for fertilizing the pond water. It is believed that 1 kg grass carp can produce sufficient manure to raise 0.5 kg of silver carp and bighead. Grass left unconsumed by fish will also become manure. Besides grass, pond dikes and farmland are often used in China for growing vegetables, corn, bananas, rice, wheat and mulberry. Wastes from all these plants are used as feed or fertilizer. The mixture of water and fertilizer that runs off from mulberry plots into ponds acts as efficient fertilizers for promoting growth of plankton. Corn, rice, and wheat are considered as the main supplementary feeds for fish. Generally the bran and broken grains are used to feed fish and livestock. Mulberry leaves are used for silkworm production, but a considerable amount of wastes (up to 18 000 kg of wastes per ha) can be obtained for use as fertilizer or feed in ponds. Silkworm pupae are used as a direct supplementary feed. Fruit trees and vegetables appear to make marginal contributions to the food and fertilizer resources of ponds.
The main contribution that fish ponds make to the productivity of integrated farms in China is in the form of silt or pond deposits, which are generally removed every year and used as fertilizer for land crops. The droppings of fish may enrich the silt. About 75 000 kg of silt may be obtained per year from a ha of pond, and silt is considered to be a high quality fertilizer. According to one estimate silt from 1 mu of pond can be used as a base fertilizer for 2 mu of rice fields. In pond manuring experiments elsewhere, not much deposit of silt has been observed when manuring is done on a daily basis. The rate of deposit of silt under different manuring practices, its composition and the effect of its partial or total removal from the pond bottom, have yet to be evaluated.
Heavy manuring, dense stocking with several species, multiple stocking and harvesting together with supplemental feeding, have produced phenomenal yields of up to 22 tons/ha under Chinese conditions. A large volume of empirical knowledge has accumulated on the practices involved. However, a clearer knowledge of the pond dynamics has to be obtained, including a definition of the pathways which convert relatively crude organic inputs into fish. The relative nutrient values of animal and plant wastes have also to be determined. The composition of manures may depend on the food that the animals eat. The role of microbes in the mineralization of wastes and their subsequent effects on the production and composition of plankton and other benthic organisms, are not clearly known. The relative importance of these organisms, including the bacteria as direct fish food, is also not clearly known. The role of the pond bottom, especially in the 2 to 3 m deep ponds in China, needs to be studied with special reference to the soil-water interface in order to rationalize manuring practices. In other countries shallower ponds are generally used. It may be that in deeper ponds photosynthesis will be limited to the upper layer which in turn may affect overall productivity. Comparative studies will be necessary to establish optimum depth and size of ponds and water management methods for efficient utilization of wastes.
The use of aerators is fairly widespread in China. The role of different types of aerators in deep and in shallow, waste-laden and densely stocked ponds needs to be studied, to determine their economic efficiencies.
The frequency and methods of manuring adopted in China differ in many respects from those of other countries. Although washings from pigsties, cow sheds and chicken pens used to be applied directly into ponds, the present practice in most areas is to ferment them for 10 to 15 days before application. Manuring is generally done only at such intervals (10 to 15 days) and the quantity applied can generally be controlled. The efficiency of this method compared to the general practice of direct daily application of fresh manure needs to be verified. Presently, about 225 000 kg of manure slurry is applied to a hectare of pond, containing about 11 250 kg of fish. In Wuxi area, the general practice is to apply 60 percent of the estimated total manure required from January to May, when the water temperature ranges from 5°C to 25°C, and the remaining 40 percent in the period of June to September at a water temperature range of 20 C to 30°C. Multiple harvesting and stocking are practised during the later part of the growing period (June to September). The rationale behind this practice has to be investigated in order to determine the optimum quantities of different manures to be applied in the most suitable form and the best method of application at different temperatures, oxygen concentrations and BOD. Many farmers report that despite all improvements, including the use of aerators, production through manuring alone reaches a plateau after a certain stage, and further increases are possible only through feeding. This would indicate the need for formulating and preparing suitable supplementary feeds, preferably based on ingredients produced on the farm.
While discussing with farmers and commune officials, one is struck by the amount of data that have accumulated. Even though they may be rather empirical, it would appear that they may prove adequate for a preliminary modelling exercise which could be refined or modified when experimental data become available. Such models may help in making general recommendations on the nature and extent of integration that can be adopted under different agro-climatic and socio-economic conditions. Intensive fish farming is often associated with risks of disease, resulting in large-scale mortality. However, from local interviews it is reported that there are no observed differences in the occurrence of diseases between integrated and non-integrated fish farms. It will be most useful to verify this and to determine whether the use of animal and plant wastes cause any public health hazards through the transmission of pathogenic organisms.
A major objective of integrated fish culture is to reduce operating costs and maximize the farmer's income. The newly established integrated fish farm of Ho Le Commune in Wuxi clearly shows how overall production and income can be progressively increased. In five years, after its establishment in 1975, the farm has increased its fish production almost nine times and the production of pigs, chicken, ducks, eggs and milk, three to five times. (The farm, with a total area of 77 ha has 67 ha of fish ponds, 1 650 pigs, 20 000 ducks, 100 cows and 8 000 chickens.). The total income in 1980 was Yuan 2.6 million1, out of which Yuan 950 000 was obtained by sale of fish. Production is planned in such a way as to reflect a balance between the output of fish and other products. The average income of an ordinary farmer was Yuan 1 000 per head per year and of the managerial staff, Yuan 1 600, which is much above the average income in this area.
The productivity of manpower is reported to be greatly enhanced through integrated farming. In Wuxi area One man can look after 2 640 m2 to 3 300 m2 of fish ponds and produce 1 500 to 2 000 kg of fish, whereas On a non-integrated farm one man can manage only 990 m2 of fish pond and produce about 750 kg of fish.
Economic data of the type indicated above together with detailed cost and earnings data will be needed to determine the benefits Of different types of integrated farming.