Metabolic responses of Nile tilapia Oreochromis niloticus to methionine and taurine supplementation

The effects of methionine and/or taurine supplementation on growth performance, amino acid profile, and gene expression of enzymes related to sulfur amino acid metabolism were evaluated in Nile tilapia (Oreochromis niloticus) in an 8-week feeding trial. A 2 x 2 factorial arrangement was designed to evaluate methionine (deficient or adequate) and/or taurine supplementation in soy-based diets. Two additional diets were included to assess the effects of excess taurine and methionine (EXC) or fishmeal protein (FM control) on the metabolism by orthogonal contrasts. All experimental diets were isonitrogenous (313.3 g kg(-1)) and isoenergetic (16.2 MJ kg(-1)) and fed to triplicate groups of 15 fish each (initial weight 6.70 +/- 0.08 g). Reduced growth performance was observed in fish fed diets containing inadequate levels of methionine without taurine supplementation (SB diet), compared to fish fed other treatments. Taurine concentration in whole-body, muscle, liver and plasma were affected (P < 0.05) exclusively to dietary taurine supplementation. Significant (P < 0.05) interactions between dietary taurine and methionine were observed with methionine concentrations in muscle and plasma, indicating a sparing effect of dietary taurine. The highest mRNA levels of S-adenosylhomocysteinase (ACHY) and cystathione beta-synthase (CBS) genes were observed in fish fed methionine-deficient diets with or without taurine supplementation. No statistical difference was observed in cysteine dioxygenase (CDO) expression (P > 0.05). In conclusion, dietary taurine supplementation demonstrated a sparing effect on the methionine requirement of Nile tilapia.