Effect of Dietary Tryptophan Levels on Growth and Hemato-Immunological Parameters in Juvenile Nile Tilapia Oreochromis niloticus

An 8-week feeding trial was conducted to evaluate the effects of dietary tryptophan on growth performance, feed utilization, hematological parameters and non-specific immune responses of juvenile Nile tilapia. Six isonitrogenous and isoenergetic diets were formulated to contain graded levels of L- tryptophan (0.102%, 0.171%, 0.223%, 0.284%, 0.331% and 0.391% of dry weight respectively) from dietary ingredients and crystalline tryptophan. Each diet was randomly assigned to triplicate groups of 25 juvenile fish (1.41±0.01g) three times daily (8:30, 12:30, and 17:00 hours) to apparent satiation. Results showed that weight gain (WG) and special growth rate (SGR) increased with increased dietary tryptophan levels up to 0.284% and remained nearly the same thereafter. Dietary tryptophan requirement was best expressed by the quadratic regression equation y=-6251x2+3525x+538.1 R²= 0.895; based on weight gain against dietary tryptophan levels, with optimal dietary tryptophan requirement estimated to be 0.282% of the diet; corresponding to 6.24% of dietary protein on a dry weight basis. Tryptophan supplementation had no impact on the survival rate, body composition, antioxidant activities, hematological parameters, and non- specific immune parameters of tilapia. Our study indicated that tryptophan supplementation enhanced growth and promoted normal physiology. Our findings could be useful in the aquaculture industry.