Dietary tryptophan requirement of fingerling Channa punctatus (Bloch) based on growth, hematological parameters, intestinal enzymes, non-specific immune response, and antioxidant capacity

Abstract

In this investigation, the tryptophan requirement of C. punctatus fingerling (5.45 ± 0.07 g) was determined by feeding seven isoproteic (450 g kg−1 CP) and isoenergetic (14.7 kJ g−1 DE) diets with graded levels of tryptophan 1, 2, 3, 4, 5, 6, and 10 g kg−1, respectively to randomly stocked groups in triplicate at 8:00, 12:30 and 17:30 h near to satiety for 12 weeks. Tryptophan contributed by casein and gelatin in basal diet was 1 g. To attain the desired tryptophan levels 0, 1, 2, 3, 4, 5 and 9 g kg−1 crystalline tryptophan was added to basal diet. The analyzed value of tryptophan in the experimental diets was found to be 0.9, 1.5, 2.6, 3.3, 4.7, 5.4 and 9.1 g kg−1, and were designated as Tr0.9, Tr1.5, Tr2.6, Tr3.3, Tr4.7, Tr5.4 and Tr9.1. Significant enhancement (P < 0.05) was found in Absolute weight gain (AWG), specific growth rate (SGR), protein retention efficiency (PRE), protein gain (PG), and RNA/DNA ratio with increasing tryptophan content up to 4.7 g kg−1 dry diet. Carcass protein and fat also improved significantly up to 4.7 g kg−1 tryptophan content. Hematological indices such as hematocrit, hemoglobin, red blood cell counts, erythrocyte sedimentation rate were positively affected (P < 0.05) up to 4.7 g kg−1 tryptophan content of the diet. Serum protein, glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT), and lysozyme were also positively correlated (P < 0.05) up to 4.7 g kg−1 dietary tryptophan content while malondialdehyde (MDA), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) showed the inverse pattern. On subjecting the AWG, FCR, PRE, PG, RNA/DNA ratio, Hb and SOD against dietary tryptophan content to quadratic regression analysis, the tryptophan requirement was found at 5.43, 5.5, 5.21, 4.96, 4.81, 4.85 and 5.39 g kg−1 diet, respectively. Based on the parameters mentioned above, the addition of tryptophan in feed in the range of 4.81–5.5 g kg−1 is recommended for formulating tryptophan balanced, practical feeds for this fish.