EVALUATING THE DIETARY TAURINE REQUIREMENT OF HYBRID STRIPED BASS Morone chrysops × M. saxatilis

A dietary requirement for the sulfonic acid taurine has been documented in many marine species. However, it has not been well studied in hybrid fish with fresh water and marine genes, such as the hybrid striped bass (Morone chrysops x M. saxatilis). Therefore, an 8- week feeding trial was conducted to evaluate the effects of varying levels of dietary taurine on growth performance, health, and body comp osition on  juvenile hybrid striped bass. Six diets were formulated to contain 38% crude protein (CP) (88% of the protein provided by soy-based ingredients and 12% from menhaden fish meal) and 12 % lipid. In four diets, the sulfur amino acid dl-methionine was supplemented to achieve a level of 1 % of dry weight, and  taurine was supplemented incrementally at 0, 0.5, 1, and 2 % of dry weight.  Two additional diets were prepared to be marginally deficient in methionine (0.8% by weight) and either supplemente d with or without taurine at 1% dry  weight to evaluate the potential interactions between methionine and taurine. All diets were fed to triplicate groups of  17 juvenile hybrid st riped bass  averaging 9.75 ± 0.027 g/fish that were randomly assigned to eighteen, 110-L aquaria connected as a recirculating aquaculture system at the Texas A&M Aquacultural Research and Teaching Facility.  Fish were fed twice daily at a percent of body weight which approached  apparent  satiation and  was  adjusted weekly.  Diets containing increment levels of taurine were analyzed using  one-way ANOVA  with the  JMP Pro 14 software  and determined to show no significant (P > 0.05) differences in terms of growth performance, feed efficiency ratio (FER), whole-body composition , hepatosomatic index (HSI), intraperitoneal fat ratio (IPF ratio),  and muscle yield. Responses of fish fed diets with and without supplemental taurine (0 and 1%) and methionine (0.8% or 1% total methionine) were analyzed by two-way factorial ANOVA on JMP Pro 14 software. Hybrid striped bass fed the methionine- deficient diets had significantly (P < 0.05) reduced percentage weight gain as well as reduced muscle yield and HSI compared to the fish fed the methionine- supplemented diet.  Interestingly, taurine inclusion at 1 % in the diet containing 0.8% methionine  statistically increased  weight gain and feed efficiency of fish compared to those fed the diet without supplemental taurine or methionine. Thus , taurine inclusion  in the diet  significantly improved growth performance of hybrid striped bass when methionine was limiting .  Analysis did not show a statistical interaction  between methionine and taurine (positive or negative) on growth performance or body composition when each  nutrient was supplemented at 1%. In  conclusion, the  growth performance and body composition  of hybrid striped bass  did not respond to taurine supplementation when dietary methionine was adequate, but did respond when dietary methionine was limiting.