Determination of dietary phosphorus requirement of stinging catfish Heteropneustes fossilis based on feed conversion, growth, vertebrae phosphorus, whole body phosphorus, haematology and antioxidant status

A 12-week feeding trial was conducted to determine the dietary phosphorus requirement of Heteropneustes fossilis fingerlings (7.7 +/- 0.04 g). Fish were fed caseingelatine-based purified diets in triplicate groups near satiation with seven different levels of dietary phosphorus (3.2, 5.2, 7.2, 9.2, 11.2, 13.2 and 15.2 g/kg dry diet). All diets were formulated to be isoproteic (400 g/kg) and isoenergetic (17.89 kJ/g). Highest absolute weight gain (68.38 g/fish), best feed conversion ratio (1.48), protein retention efficiency (30.74%), protein gain (12.44 g/fish), haemoglobin (11.19 g/dL), RBCs (3.12 x10(6) /mm(3)), haematocrit (33.44%) and serum phosphate (2.82 mg/L) were found at 9.2 g/kg phosphorus. Hepatic superoxide dismutase and catalase activity were also significantly influenced by the dietary phosphorus levels. Whole body and vertebrae phosphorus concentrations increased significantly as the amount of dietary phosphorus increased from 3.2 to 11.2 g/kg dry diet and then plateaued. More accurate information on dietary phosphorus requirement was obtained by subjecting the AWG, FCR, vertebrae phosphorus and whole body phosphorus concentrations data against various levels of dietary phosphorus to broken-line analysis, which yielded the requirement in the range of 9.0-11.0 g/kg for optimum growth and mineralization of H. fossilis.