Taurine and methionine supplementation as a nutritional strategy for growth promotion of meagre (Argyrosomus regius) fed high plant protein diets

The effect of methionine and taurine supplementation of plant protein based diet for meagre (Argyrosomus regius) juveniles was assessed on growth performance and metabolic hepatic enzymes activity. For that purpose, four isolipidic (180.0 g kg(-1) crude lipids) and isoproteic (420.0 g kg(-1)) practical diets were formulated containing 820.0 g kg(-1) of protein from plant origin and 180.0 g kg(-1) from fishmeal. A 2 x 2 factorial arrangement of treatments was used with methionine at 7.5 and 10.0 g kg(-1) dry diet, supplemented or not with taurine at 10.0 g kg(-1) dry diet. The feeding trial was conducted with fish of 50.0 +/- 0.6 g mean initial body weight and lasted for 65-day. Dietary taurine supplementation improved growth and feed utilization while methionine supplementation had no effect. Diets did not affect whole-body and liver composition. No interaction was observed between the supplemented amino acids. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities increased only with taurine supplementation, while glutamate dehydrogenase (GDH) activity was unaffected by dietary treatment. Fructose-1,6-bisphosphatase (FBPase) activity was affected both by methionine and taurine supplementation. In conclusion, dietary methionine supplementation was inefficient to overcome the decreased taurine level in plant-based diets and thus, taurine should be incorporated in plant protein-based diets, as an efficient nutritional strategy for the mitigation of growth limitations of meagre fed diets with high levels of plant feed ingredients. Moreover, as growth performance was not improved by increasing dietary methionine this suggests that under our experimental conditions meagre requirements are met with 7.5 g kg(-1) dietary methionine.