Abstract
Amino acids are vital for all living organisms including fish and histidine is an essential amino acid for fish. In view of this, dietary histidine requirement of fry Heteropneustes fossilis was determined by feeding casein-gelatin-based isonitrogenous (430 g kg(-1) CP) and isocaloric (17.9 MJ kg(-1) GE; 15.5 MJ kg(-1) DE) amino acid test diets (10 to 20 g histidine kg(-1) dry diet) to quadruplicate groups of randomly assigned fish to apparent satiety for 12 weeks. Maximum absolute weight gain (AWG; 44 g fish(-1)), protein retention efficiency (PRE; 20%), protein efficiency ratio (PER; 1.04), haemoglobin (Hb; 11.24 g dL(-1)), haematocrit (Hct; 35.11%), red blood count (RBCs; 2.98 x 10(9) mL(-1)) and lowest erythrocyte sedimentation rate (ESR; 1.92 mm h(-1)) were obtained at 16 g histidine kg(-1) dry diet. The 95% maximum quadratic response of above data exhibited the requirement to be at 15.2, 15.1, 15.6 and 15.5 g histidine kg(-1) diet. As histidine is found in higher concentration in haemoglobin, requirement obtained for Hct% and Hb is 4% greater than that required for maximizing weight gain and protein retention. Based on these results, dietary histidine requirement of H. fossilis fry is recommended between 15.1 and 15.6 g kg(-1), corresponding to 35.1-36.3 g kg(-1) protein.