Submitted to: Aquaculture Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 23, 2005
Publication Date: October 17, 2005
Citation: Gaylord, T.G., Rawles, S.D., Davis Jr., K.B. 2005. Dietary tryptophan requirement of hybrid striped bass (Morone chrysops x M. saxatilis). Aquaculture Nutrition. 11:367-374. Interpretive Summary: Like most other animals, fish require specific minimum amounts of the same ten amino acids, which are the building blocks of protein. In hybrid striped bass, dietary requirement levels for six of these ten essential amino acids are unknown. In this study, we quantified the requirement for the essential amino acid tryptophan in hybrid striped bass. The requirement level for tryptophan was quantified by fitting mathematical models to growth and body composition data that were collected after the fish had been fed diets that contained increasing amounts of this essential amino acid. Fifteen diets were formulated that contained equal amounts of protein and energy but also contained increasing amounts of tryptophan. Tryptophan concentration in the diets ranged from 0.1% to 1.4% of diet. This range of concentrations was chosen in order to bracket the amounts of tryptophan in the diet that would be considered too low (deficient) to too high (inhibitory). After 5 weeks of feeding, only 40% of the fish receiving the lowest level of tryptophan (0.1% of diet) were still alive. The remaining fish fed this diet were in poor health. Survival of fish receiving the next higher level of tryptophan (0.03%) had declined to 70% by the end of the trial. Survival in all other treatments was 100%. Fish receiving at least 0.16% dietary tryptophan more than doubled their starting weight. Liver size, fillet yield and body fat also changed as the amount of tryptophan in the diet changed. Body fat decreased as the amount of tryptophan in the diet increased. Based on the mathematical models that were used to fit the data (saturation kinetics models), hybrid striped bass require between 2.1 to 2.5 g tryptophan per kg of diet (0.6 to 0.7 g/100 g protein). These findings will increase the precision of diets formulated for hybrid striped bass.
Technical Abstract: Knowledge of the nutritional requirements of hybrid striped bass has been rapidly improving over the last decade. Of the ten indispensable amino acids (IAA), requirements for four'arginine, lysine, threonine and the total sulfur amino acid'have been quantified for this taxon. In this study, we estimate the requirement of hybrid striped bass for L-tryptophan by nonlinear regression analysis of several growth indicators in response to dietary concentrations of this IAA. Fifteen isocaloric, isonitrogenous diets were formulated to contain increasing levels of L-tryptophan in order to bracket the dietary concentrations considered deficient to inhibitory. Tryptophan concentration ranged from 0.1% in the basal diet to 1.4% of diet at the highest level of inclusion. After 5 wk, survival of fish receiving the basal diet was 40% while the remainder of fish fed this diet were in poor health. Survival of fish receiving 0.03% supplemental tryptophan had declined to 70% by termination of the trial. Survival in all other treatments was 100%. Fish weight gain was 100% or greater for fish receiving 0.16% dietary tryptophan or more. Hepatosomatic index (HSI), muscle ratio (MR) 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 to 2.5 g/kg diet (0.6 to 0.7 g/100 g 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.