Effects of dietary taurine on growth performance, antioxidant status, digestive enzymes activities and skin mucosal immune responses in yellowfin seabream, Acanthopagrus latus

An eight-week study was carried out to investigate the impact of supplementing crystalline taurine (Tau) in diet for yellowfin seabream (Acanthopagrus latus) (0.6 +/- 0.0 g) fry. Fish meal (FM) in a basal diet was partially (Ca. 50%) replaced with blends of plant protein sources (soybean and corn gluten meals) and graded levels of crystalline Tau including: 0 (control), 2, 4, 8, 12 and 16 g kg(-1) were included to the basal diet to create experimental feeds. The amino acid profiles of the experimental diets were evaluated and the total Tau content (crystalline TAU + FM derived Tau) that was determined in the experimental diets were as follow: 2.3 (control), 3.5 (2), 5.5 (4), 9.6 (8), 12.5 (12) and 16.5 (16) g Tau kg(-1), respectively. Fish fed on the Tau-supplemented diets had a significant positive linear trend in growth rate and feed conversion ratio. The essential amino acids including leucine and lysine gradually increased with increasing dietary Tau level and showed positive linear trends. In addition, Tau content in fillet had positive linear and quadratic trends in response to dietary Tau level. Fish fed Tau-supplemented diets had a significant positive linear trend regarding to liver catalase activity, meanwhile a positive quadratic trend was noticed between dietary Tau level and glutathione peroxidase activity. In addition, the liver superoxide dismutase activity and glutathione level showed positive linear and quadratic trends in response to dietary Tau level. Moreover, the concentration of MDA in the liver decreased with increasing dietary Tau level and showed a positive quadratic trend. The activities of trypsin and alkaline phosphatase increased with enhancing dietary Tau concentrations and showed an obvious quadratic trend. Skin mucosal total protein and albumin levels showed positive quadratic trends with dietary Tau level. The skin mucosal lysozyme and alternative complement activities enhanced with increasing dietary Tau level up to 12.5 g Tau kg(-1) and they showed positive quadratic trends. According to the findings of this research, the optimum dietary Tau content in A. latus fry was estimated to be 10.7 g kg(-1) diet according to break-point regression method by plotting feed conversion ratio and specific growth rate against dietary Tau levels.