Abstract
The effect of substitution of fishmeal by soybean meal in diets on the growth performance of Indian major carps, Labeo rohita and Cirrhinus cirrhosus along with some aspect of their breeding biology were studied under laboratory and field conditions from July 2003 to October 2005. Four isonitrogenous (30%) and almost isocaloric diets were tested for L. rohita and C. cirrhosus separately for 60 days in laboratory aquaria. The diet in which 25% and 50% fishmeal were replaced by soybean meal for L. rohita and C. cirrhosus, respectively gave significantly better (P<0.05) result in terms of growth, SGR (%/day), FCR and PER without supplementation of amino acid. Histological study showed irregularity in hepatocytes in cases where the rate of replacement of fishmeal by soybean meal was 50% (L. rohita) and above (C. cirrhosus). Effects of soybean meal based diet on gonad development and breeding performance of L. rohita and C. cirrhosus were studied for 13 months in nine earthen ponds. Optimum gonad development, breeding performance and better spawn production were shown by fishes fed with a diet where 60% fishmeal was replaced by soybean meal. The highest growth and survival rate after 42 days of spawn rearing at a stocking density of 750,000 ha1 under monoculture were found in Treatment 2 where 75% fishmeal protein and 25% soybean meal protein were used in diet. But benefit cost ratio of this Treatment was not significantly different from that of Treatment 3 where 50% fishmeal protein and 50% soybean meal protein were used. The growth of carps' fry were studied at 1,50,000 ha1 stocking density in 12 ponds with four isonitrogenous (35% protein) and almost isocaloric diets of different combinations, when 0%, 25%, 50% and 75% fishmeal protein were replaced by soybean meal. Growth of fish fed with 50% fishmeal protein and 50% soybean meal protein diet was significantly higher (P<0.05) than those fed with the other diets. The best SGR (%/day), FCR and PER were also observed in the above case. Histological study showed that in all the Treatments granular cytoplasm and thyroid follicles were evenly distributed in hepatocytes. Two formulated diets containing 30% and 60% soybean meal protein were compared with 100% fishmeal protein based diet in a grow-out experiment with L. rohita and C. cirrhosus at 15,000 ha1 stocking density. After seven months culture, growth performance of both the species were found significantly better (P<0.05) in Treatment 3 where 60% soybean meal protein and 40% fishmeal protein were used in the diet in terms of final weight, SGR (%/day), FCR and PER. The gross production and benefit cost ratio were also higher in Treatment 3.