Effects of varying levels of dietary l-histidine on growth, feed conversion, protein gain, histidine retention, hematological and body composition in fingerling stinging catfish Heteropneustes fossilis (Bloch)

Heteropneustes fossilis is distributed in most of the Southeast Asian countries. It is a promising species for aquaculture due to its high protein and iron content, ability to withstand shifts in salinity and temperature, and survival in oxygen depleted water. In view of the above, this study was undertaken to evaluate the effects of varying levels of dietary l-histidine on growth, protein gain, histidine retention, hematological and body composition of this fish so as to optimize the inclusion of histidine in its commercial feeds. Casein-gelatin based isonitrogenous (380 g kg− 1 CP) and isocaloric (17.9 MJ kg− 1 GE; 15.3 MJ kg− 1 DE) amino acid diets with six different l-histidine levels (5.0, H1; 6.5, H2; 8.0, H3; 9.5, H4; 11.0, H5; 12.5 g kg− 1dry diet H6) were fed to quadruplicate groups of fingerling Singhi (6.6 ± 0.2 g) twice daily at 07:00 and 17:30 h to apparent satiation for 8 week. Feeding trial was conducted in a flow-through system (1-1.5 L min− 1) at 28 °C water temperature. Growth, feed conversion, protein gain and histidine retention of fingerling Singhi were found to increase significantly with the quantitative increase in dietary histidine from 5.0 (H1) to 9.5 g kg− 1 diet (H4). Hepatosomatic index, condition factor, hematocrit and hemoglobin were significantly affected in fingerling Singhi fed different concentrations of histidine and were also found to be best in fish fed diet H4. Quadratic regression analysis of the above parameters at 95% maximum and minimum plateau indicated that inclusion of histidine at 9.4 g kg− 1 of the dry diet, corresponding to 24.8 g kg− 1 dietary protein is optimum in formulating histidine-balanced, cost-effective, commercial feeds for intensive culture of Singhi.