30 March 2012 feed fish. For good growth, a 1:1 ratio of oil cake to rice bran is used. However, cost is the key factor in feeding fish and farmers have to regulate the level of oil cake in such a way that best results are obtained without wastage. In winter, the feed conversion efficiency is low and farmers in Andhra Pradesh avoid using oil cakes in this season. As a general rule, with a good amount of natural food, the farmer provides 1.5-2.0 kg of rice bran and oil cake mixture as a supplementary feed. Feeding strategy Feed the fish daily and ensure that feed is given either in tray or in feed bags that can be made with fertilizers bags (Figures 6 and 7). The bag feeding method developed by farmers in Andhra Pradesh prevents the wastage of feed to a great degree and well-trained fish generally exhaust feed within one to two hours from the time of feeding. Even feed given in small quantity should be provided daily. Adding up to 1% salt in the feed can improve fish growth and reduce stress. Use bamboo as substrate When placed in water, bamboo provides good surface area for the growth of periphytic food organisms and these are actively grazed by rohu, common carp, tilapia, gonius (Labeo gonius), and small cyprinids (Figure 8). Evolved by fishers, this is an age-old technique to aggregate fish by dumping tree branches in rivers and lakes, and capturing them. This traditional technique, which has been investigated scientifically, is an effective approach to increase the growth of fish and crustaceans, such as freshwater prawns. In species such as rohu that have special fringed lips, the growth increment was up to 60% greater than fish in ponds without substrate. As little as a 20-30% increase in growth would bring a substantial amount of revenue. Hence, it is recommended that farmers use tree branches or bamboo as substrate in the pond (Figure 9). Ponds are installed with an equivalent of 50% of the pond surface area with bamboo substrate, about 4-5 pieces per m2, depending on bamboo diameter. In addition to promoting growth, bamboos will prevent poaching of fish from the pond because poachers cannot operate nets easily without removing bamboo. Choose the right species for culture Effectiveness of the practices described above depends on the species cultured. Chinese carps, including common carp, grass carp, and silver carp have not been used by Andhra Pradesh farmers for various reasons. They culture mostly rohu (almost 90% of fish stocked), with the remainder being catla only or catla mixed with mrigal. Farmers of Andhra Pradesh target the eastern India market where demand for rohu is high. This species also grows well in high temperature locations with a large water surface area. In contrast to Andhra Pradesh, Chinese carps are best suited in northeastern India because of temperature. Chinese carps grow well as long as feed is made available, irrespective of pond size. If fed well, grass carp can help several other species to grow. Silver carp is best suited to harvest the plankton and demonstrates good growth. Further, minor /medium carps, such as Fig. 4. Pig manure can increase pond productivity. Fig. 5. The access to fish ponds by ducks is restricted to one area. Fig. 6. Providing bagged feed to increase fish productivity.
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