Carbon, Nitrogen and Phosphorus Budget for the Culture of Indian Major Carps with Different Stocking Density

Nutrient budget was performed for the culture of Indian major carps; Catla catla (catla), Labeo rohita (rohu) and Cirrhinus mrigala (mrigal) in twelve fishponds, each of 0.04 ha water area. The stocking densities of carps were 7,500; 10,000 and 12,500 no. /ha (four replications for each stocking density and the ratio of each species was 1:1:1) and the average weights of catla, rohu and mrigal fingerlings were 6.5 ± 0.5, 5.0 ± 0.4 and 3.5 ± 0.4 g, respectively. The culture period was six months. Cow dung@14,000 kg/ha/yr was applied fortnightly as manure. Urea@200 kg/ha/yr and single super  phosphate@300kg/ha/yr were applied fortnightly as fertilizers. The fish were fed with an admixture of groundnut oil cake and rice polish in the ratio of 1:1@2% body weight of their biomass. The budget showed that recovery (in terms of fish yield) of nitrogen (N) decreased from 43 to 24% and the same for phosphorus (P) also decreased from 16 to 9% with increase in stocking density. The recovery of organic carbon (OC) decreased from 28 to 16% with increase in stocking density from 7,500/ha to 12,500/ha. Effluent water (pond water at the time of harvest) accounted for 1.8 to 3.0% N, 2.5 to 4.0% P and 2.5 to 5.0% OC of the total inputs while bottom sediment accounted for 41 to 50% N, 70 to 75% P and 62 to 64% OC of the total inputs, respectively. Nutrient accumulation increased in both the effluent water and bottom sediment with increase in stocking density.