Abstract
This study was conducted to assess the optimum dietary tryptophan requirement of fingerling Indian major carp, Labeo rohita (3.90 +/- 0.05 cm; 0.37 +/- 0.040 g), by feeding diets containing six levels of tryptophan to apparent satiation. Casein-gelatin-based isonitrogenous (40% crude protein) and isocaloric (4.28 kcal/g gross energy) amino acid test diets simulating the amino acid profile to that of 40% whole chicken egg protein except for tryptophan were formulated. Growth performance of the fish was evaluated on the basis of live weight gain (LWG), feed conversion ratio (FCR), protein efficiency ratio (PER), and protein productive value (PPV) data. Maximum LWG (568.7%), best FCR (1.28), and highest PER (1.95) were recorded at 0.40% tryptophan of the diet. Dietary tryptophan levels significantly (P < 0.05) affected body composition of the fish. However, maximum body protein (18.85%) and PPV (0.36) were obtained for the group receiving dietary tryptophan at the level of 0.35% of dry diet. Based on the second-degree polynomial regression analysis of the LWG%, FCR, PER, and PPV data, the optimum requirement of fingerling L. rohita for l-tryptophan is recommended in the range of 0.36-0.38% of the diet, corresponding to 0.90-0.95%, respectively, of the dietary protein for growth and efficient feed utilization.