Fish farming in irrigation systems: Sri Lanka and global view
C H FERNANDO and M HALWART
The enterprise of harvesting fishes from rice fields is widespread in the tropics and is an ancient practice. The culture of fishes in rice fields is less wide spread and had its origins a few millennia ago in China and India. The practice of fish culture was spread from China to Japan, Italy and the former Soviet Union during the past 150 years or so. It was adopted in Indonesia under Dutch colonial rule. In the past 50 years or so various forms of fish culture in rice fields has spread sporadically into countries mainly in Asia but also into Malagasy and even Slovakia. All these attempts to culture fishes in rice fields have either survived as in Malagasy, Indonesia, Laos and Vietnam at a relatively low level of success or have died out as in Italy, Soviet Union, Japan and Slovakia.
A good understanding of the biological processes and ways to supply water in adequate amounts is necessary for sustained fish farming in irrigation systems. In traditional systems as in China and India a practical knowledge of the ecological situation was available to the farmers. However, this level of knowledge is not sufficient to raise fishes in irrigation systems at the present time at a profit just as growing rice and wheat with only traditional knowledge is able to compete with modern agriculture. We have explored traditional and modern methods of fish farming in rice fields. The literature on the subject is very scattered in and in many languages. Improved agronomic practices are dependent on the availability of water, the control of pests and breeding of high producing varieties of rice. Rice - fish culture also depends on these factors being favorable. Recent advances in the conservation of water and the reduction of pesticide use offer promise to improve both rice and fish production. So far the spectacular increases in rice production have been achieved with better strains of rice and other conventional methods. Perhaps fish culture in rice fields and other segments of the irrigation system can also benefit from improved breeds of fish. Some progress has been made in this direction with fast growing GIFT (Genetically Improved Farm Thilapias). Molecular biology and biotechnology are likely to push up yields of both fish and rice in irrigation systems. However, their role in food production is somewhat blurred by the controversy about GM foods.
The chequered history of fish farming is further complicated by the lack of consistent data on fish production in rice fields and irrigation channels. Reservoirs have better statistics. Rice is the main crop and fish a minor one and this means that we do not have data on fish in rice fields except in rare instances. In recent years the improvement of standards of living and the availability if tilapias of better quality than carps has made rice fiel