62 JUNE 2017 • WORLD AQUACULTURE • WWW.WAS.ORG recent years, cage culture in reservoirs has also received attention from researchers, development agencies and policymakers. Candidate Species Selection of species for cage culture should be customized on the basis of economic and nutritional value, regional preferences, market demand and product value, the hardy and tolerant nature of the species and acceptance of external sources of food under confined conditions. Cages can be used for raising fingerlings or production of table-size fish. The striped catfish Pangasianodon hypophthalmus (pangas) has achieved great importance as a candidate species for cage farming in India. The average productivity of pangas in cages is 50 kg/m3 at a stocking density of 40-70/m3 (40-50 mm seed). Fish are fed floating feeds with a crude protein content ranging from 20-30 percent. A feed conversion ratio of 1.3-1.5 and a benefit to cost ratio of 1.48-1.85 can be obtained for table-size pangas production. By way of comparison, a benefit cost ratio of 2.24-2.50 can be obtained for production of Indian major carps in cages (Sharma et al. 2016). Pangas, monosex tilapia, GIFT tilapia, common carp, and Jayanti rohu Labeo rohita are the major species cultured in cages. Sometimes rohu are stocked in the outer net of double-net cages because they will clean algal bioflouling on nets. Other candidate species — including Puntius javanicus, Labeo bata, Lates calcarifer, Macrobrachium rosenbergii, various air-breathing fishes and ornamental fishes — also have been introduced into reservoirs with varying degrees of success. These indigenous species have potential for diversification of cage culture: Labeo bata, Cirrhinus reba, L. rohita, Osteobrama belangeri (pengba), Ompok bimaculatus (pabda), Anabas testudineus, A. cobozius, Pangasius pangasius, Puntius sarana, Lates calcarifer, Etroplus suratensis, Chitala chitala (featherback), murrels (Channa striata, C. marulius), Mystus sp., Wallago attu and Macrobrachium rosenbergii. Cage Types Cages of different size, shape and material are used in India. Initially bamboo cages of various dimensions were used for raising fish seed in reservoirs and wetlands (Manna and Hassan 2004). Later galvanized iron (GI) frame cages were introduced and became popular. At present GI cages account for almost 80 percent of all cages installed in reservoirs. Pangas are grown in GI or HDPE-frame modular cages (DoF, Jharkhand and Chhattisgarh). Modular ‘pontoon type’ fiberglass or HDPE cages are getting popular. Presently there are more than 1000 pontoon-type cages in operation for fish culture. Newgeneration cage designs with dimensions of 5 × 5 × 4 m or 6 × 6 × 4 m are also becoming popular in reservoir cage culture. GI cages (6 × 4 × 4 m) with four per battery and HDPE modular cages with six per battery have proven to be suitable for fish production in reservoirs. Large rectangular cages are suitable for table-size fish production of Indian major carps. In Chandil Reservoir, Jharkhand, large rectangular cages of 36 × 16 × 5 m, 12 × 8 × 5 m and circular cages of 12-m diameter are being installed. Environmental Impact and Carrying Capacity Fish production in cages is primarily dependent on the supply of compound manufactured feed and generally a relatively small portion of the nutrients supplied in feed is transformed to fish biomass. The remaining portion is loaded into the adjacent aquatic environment. A paucity of data on the impact of cage culture on the ecological structure and function and ecosystem services provided by waterbodies pose questions on the sustainability of cage culture in open-water bodies. Although India is moving quickly to develop cage culture, no studies that estimate carrying capacity of water bodies used for cage culture have been made. Therefore, to properly evaluate cage culture in reservoirs of India, studies on carrying capacity and impact assessment are needed to maintain the ecological integrity of reservoirs and the sustainability of fish production in cages. A Way Forward Considering India’s rich and varied open-water resources, culture of fish in cages offers enormous scope for increasing fish production. Using only a modest fraction of their surface area, large and medium reservoirs can make a substantial contribution to inland fish production through cage culture. Although cage culture has not yet reached the desired commercial proportions capable of making a meaningful contribution to production, it is growing at a very fast pace, giving hope but also cause for some concern. The following points offer a way forward to popularize and expand cage culture in Indian reservoirs. • Develop environmentally friendly and economically viable enclosure fish culture technologies, • Develop region- or species-specific packages of practices, • Diversify fish species cultured based on regional preference and market demand, • Develop suitable strains of desired species for cage farming, • Develop brood banks and seed production technology of regionally preferred indigenous fish species, • Develop low-pollution, cost-effective and nutritionally balanced artificial feed using locally available ingredients, TABLE 1. Potential of cage culture in Indian reservoirs. Adapted and modified from Jha et al. (2013). Resource Total area ~0.1 percent of Available volume Per unit Expected fish (ha) total area volume > 3 m production production depth (m3) (kg/m3) (1000 t) Medium reservoirs 515,749 500 15,000,000 15-25 225-375 Large reservoirs 1,293,268 1300 39,000,000 15-25 585-975 Total 810-1350
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