46 SEPTEMBER 2015 • WORLD AQUACULTURE • WWW.WAS.ORG TABLE 1. Actual and potential production from reservoirs of India (Sugunan 1995). Area (ha) Present production (t) Production potential (t) Small 1,485,557 74,200 743,000 Medium 507,298 6,500 127,000 Large 1,160,511 13,000 116,000 Total 3,153,366 93,700 986,000 Cage culture is a technology through which fish are reared while captive in an enclosed space that maintains the free exchange of water with the available water source. In India, cage culture in inland water bodies was first initiated to raise air-breathing fish in swamps, major carps in running waters in Jamuna and Ganga at Allahabad, and for Indian major carps (Labeo rohita, Catla catla, Cirrhinus mrigala), snakeheads (Channa striata, Channa punctata) and tilapia (Oreochromis niloticus) in lentic water bodies of Karnataka. Thereafter, cages in many reservoirs and floodplain wetlands have been used to produce advanced fingerlings for stock enhancement in the main water bodies (Bhowmick 2011, Karnatak and Kumar 2014). Interest in cage culture has been promoted as an alternative crop for farmers outside traditional fish farming areas and where topography is not conducive to construction of levee ponds. Potential of Fish Production from Reservoirs in India The Government of India defines reservoirs as man-made impoundments created by obstructing surface flow, by erecting a dam of any description on a river, stream or water course. Water bodies less than 100 ha have been excluded from this definition. The Ministry of Agriculture, Government of India, has classified reservoirs as small (<1000 ha), medium (1000 to 5000 ha) and large (>5000 ha) for the purpose of fisheries management, although different states have varied classifications. The estimated cumulative areas are 1,485,557 ha for small, 507,298 ha for medium and 1,160,511 ha for large reservoirs (Table 1) (Sugunan 1995). India has 19,370 reservoirs spread over 15 states, with an estimated 3.15 million ha surface area at full capacity. This is expected to increase because of the execution of various water projects in the country. Tamil Nadu state has the greatest area of small reservoirs (Sreenivasan 1989), followed by the states of Karnataka and Andhra Pradesh. The state of Madhya Pradesh has the greatest total area of small reservoirs, while Andhra Pradesh, Gujarat and Rajasthan also have a higher surface area of medium reservoirs. Karnataka has the most reservoirs with 12, but the total area is less when compared to the cumulative extent of 7 reservoirs in Andhra Pradesh (Karnatak and Vikash 2014). Potential Species for Cage Aquaculture Species selected for farming in floating net cages must have a good market demand and high market value, should be hardy and able to accept external sources of food under confined conditions. Food from external sources may include natural foods, such as trash fish, or artificial feeds, such as dry formulations. The criteria for the selection of species for cage farming are: High-value. It is preferable to culture species with high market value to offset the relatively high cost of production in cages. Because fish can be harvested easily live, the farmer can sell fish in prime, live condition. In doing this, a better price can be obtained than would be possible if fish were sold chilled or frozen, as is the usual case with fish harvested in pond culture. Hardy and tolerant. Species should also be hardy and tolerant of confined, crowded conditions and to the rigors of handling during net changes and fish transfers. Stocking in net cages is often more than 10 times that of pond culture, 5/m2 in ponds compared with 30-40/m2 in net cages for Pangasius culture, for example. Able to accept external sources of food. Inasmuch as there are usually no other significant sources of food in a net cage, selected fish must be able to accept external sources of food. Formulated feed would drop through the net cage if it were not eaten by the time it reaches the net bottom. Feeding trays can be suspended in the net cage to catch the pellets as they fall. Net cages can be deepened to allow greater time of feed retention within the net cage or a slowsinking dry pelleted feed can also be used. There are four primary groups of fishes suitable for cage aquaculture: Carps. For cage culture, the major limitations of carp are that they are not voracious eaters, growth is relatively slower in cages and they tend to accumulate more fat than protein in the body because their natural habitat is flowing waters. In cages, carps are not able to move as they are inclined to do, so proper design of cages is needed to avoid this problem and get good production. Murrels. Murrels are a type of snakehead, mainly carnivorous, with a high market demand. The major drawbacks for cage culture are that growth is extremely slow in cages, they are predatory and the seed production technology is not standardized and commercialized. Potential Species for Cage Aquaculture in Indian Reservoirs Vikash Kumar, Gunjan Karnatak, Mishal P., A.K. Das, M.A. Hassan, A.P. Sharma
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