Dietary tryptophan requirement of hybrid striped bass (Morone chrysops x M-saxatilis)

Requirements for six of the 10 indispensable amino acids (IAA) have not been quantified for hybrid striped bass. In this study, we estimate the requirement for L-tryptophan by nonlinear regression analysis of several growth indicators. Fifteen isocaloric, isonitrogenous diets were formulated to contain 1.0, 1.3, 1.6, 1.9, 2.2, 2.5, 2.8, 3.1, 3.4, 3.7, 4.0, 5.0, 6.0, 10.0 or 14 g L-tryptophan kg(-1) diet and fed to reciprocal cross hybrid striped bass for 7 weeks. After 5 weeks, survival of fish receiving the basal diet was 40% while surviving fish fed this diet were in poor health. Survival of fish receiving 1.3 g Trp kg(-1) diet declined to 70% by termination of the trial. Survival in other treatments was 100%. Fish weight gain was 100% or greater for fish receiving 1.6 g Trp kg(-1) diet or more. Hepatosomatic index, muscle ratio and intraperitoneal fat (IPF) ratio also responded to dietary tryptophan concentration. IPF was inversely related to dietary tryptophan concentration. The dietary tryptophan requirement was estimated to be between 2.1 and 2.5 g kg(-1) diet (6-7 g kg(-1) protein), depending on response variable, using four- and five-parameter saturation kinetics models. These findings will increase the precision of diets formulated for hybrid striped bass.