Tryptophan requirement in semi-purified diets of juvenile Nile tilapia Oreochromis niloticus

To further optimize practical diets with respect to IAA requirements, this study was conducted to confirm and refine the tryptophan requirement, which is a potentially limiting AA in our matrix of ingredients. In order to ensure the best information on Trp requirement, our study used wide range of Trp levels and quality of fit of the models for calculating requirement estimates. Twelve iso-nitrogenous and isoenergetic diets (practical defined ingredients) containing 30% protein and 8% lipid were formulated to meet the nutritional requirement of juvenile Nile tilapia (Oreochromis niloticus) with the exception of tryptophan. A basal diet deficient in tryptophan was assigned to meet all other known nutrient requirements of the Nile tilapia. L-tryptophan was then added to the basal diet at 0.04% increments to produce tryptophan levels ranging from 0.21 to 0.61% of the diet. The diet which supported the best performance of Nile tilapia in previous work, was used as a reference diet. Each diet was fed to three replicate groups of juvenile Nile tilapia (7.9 +/- 0.1 g) in a recirculation system for eight weeks. Saturation kinetic model, broken line models with linear or quadratic ascending portions, were used to evaluate dose-response relationships of thermal-unit growth coefficient, apparent net protein retention, tryptophan retention against dietary tryptophan. Akaike weights were calculated and used for model selection in addition to the models overall R 2. The tryptophan requirement of juvenile Nile tilapia was estimated at 0.31% (0.25-0.37%), 0.33% (0.26-0.39%), 0.25% (0.24-0.25%), 0.27% (0.25-0.31%) of the diet for optimum growth, tryptophan deposition, feed efficiency, and apparent net protein deposition (95% of maximum value), respectively.