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It has been observed that combination of rice and fish farming is mutually beneficial. Fish feed on organisms which grow in fields and on many noxious insects and their larva, thus saving the crop from harmful organisms and promoting better rice yield. By culturing herbivorous fish, the weed growth can be controlled to a considerable extent. Where there is proper water management it is possible to control the growth of molluscs and breeding of mosquitoes, thus reducing public health hazards.
Movement of fish in inundated rice fields increases tillering, which is helpful in higher rice production. Greater depth of water maintained in fields prevents pests like rodents from digging holes in bunds, and floods their existing holes. Despite benefits, the two cultures entail additional cost for farmers, particularly in management and labour, which may easily be overcome by income from fish farming.
At present three major types of rice-field aqua culture are practised. The first which is the simplest form is by using flooded rice fields after harvest, to raise one or more crop of fish or shrimp. The second is growing fish along with rice and harvesting rice and fish at the end of the rice-growing season. The third and complicated system, which ensures a prolonged period of fish culture, involves transferring the stock to specially prepared ditches, channels or pools at the time of rice harvest, and restocking them in fields for a further growing period. By this system, fish is grown to a larger size than is possible in the short duration of one rice crop.
In rice-cum-fish farming, the main crop is rice and therefore fish farming techniques have to be modified to make them compatible with rice farming. In some cases ,it is needed to reinforce and increase the height of bunds to prevent the escape of fish, but this will not affect rice farming. Construction of ditches and canals reduces the area available for rice planting, as they may occupy 5-10 per cent of the land. Higher levels of water have to be maintained (10-25 cm) for growing fish together with rice.
In areas where water supply is limited, this may prove to be a major handicap. Also the short-stemmed, high-yielding varieties used by farmers may tolerate only moderate water depths, even when water supply is not a constraint. The duration of cultivation of such varieties is shorter (105-125 days) and may not be long enough to grow fish to a marketable size. Deep water (floating) rice is suitable for combined farming. Fertility of the soil is equally important for this culture. The small additional fertiliser needed to stimulate adequate growth of fish food may not affect production costs very much. Water quality in fields has to be maintained at a level suitable for fish and its food organisms. A serious problem which has affected the culture, and contributed to its decline in many countries, is the excessive use of pesticides which kills fish. There is also risk of accumulation of pesticides in fish which may be harmful for consumers.
In rice fields irrigated with fresh water, either mono- or poly-culture of finfish is cultured. The most common species are carp, tilapia and Trichogaster. Snake-head (murrel) and catfish are also used.
As fields when flooded after rice harvest, serve as shallow ponds, some pond culture practices such as fertilisation and supplementary feeding can be adopted. Through proper water management, a suitable water temperature and oxygen content have to be maintained. Depending on the period available for fish farming, the stocking rate and size can be determined. The duration of culture is generally three to four months. Fish yield varies with species and culture practices etc. In well managed fields a yield of up to 700 kg/ha can be expected.
Source: DAWN