The present project was planned to study gradual replacement of Cirrhinus mrigala with Cyprinus carpio and its impact on pond ecosystem. A total of 900 fishes belonging to six species viz. Catla catla, Labeo rohita, Cirrhinus mrigala, Ctenopharyngodon idella, Hypophythylmichthys molitrix and Cyprinus carpio were stocked in four earthen ponds. The dimensions of each pond were 220 × 198 × 7 feet length, breadth and depth. The stocking density in pond 1 (T1) was C. catla 150, L. rohita 200, C. mrigala 200, C. idella 150, H. molitrix 150 and C. carpio 50. The stocking density of C. mrigala and C. carpio in pond 2 (T2) was 150 and 100, in pond 3 (T3), 100 and 150 and in pond 4 (T4) it was 50 and 200, respectively while the stocking density of all the other four fish species remained constant in all the four ponds. All the fish were fed with a diet of 25.16% crude protein at 2% body weight. C. idella and C. mrigala showed maximum growth in T1, C. catla and H. molitrix in T2, L. rohita and C. carpio in T3. Maximum growth was observed in T3 followed by T4, T1 and T2. Among fish species C. idella and C. carpio showed higher growth rates than the rest of fish species. Our results reveal that in polyculture system stocking density of C. mrigala and C. carpio in a ratio of 1: 1.5 gives better results.
Key words: Aquaculture, freshwater, phytoplankton, zooplankton, exotic fish.
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