Effect of N-acetyl cysteine and glycine supplementation on growth performance, glutathione synthesis, and antioxidative ability of grass carp, Ctenopharyngodon idella.

An 8-week feeding trial was conducted to evaluate the effect of N-acetyl cysteine (NAC) and glycine supplementation on growth performance, glutathione (GSH) synthesis, and antioxidative ability of grass carp, Ctenopharyngodon idella. Four practical diets were formulated: control, control + 0.2% NAC, control + 0.5% glycine, and control + 0.2% NAC + 0.5% glycine. Each diet was randomly assigned to quadruplicate groups of 30 fish (approximately 8.8 g). Weight gain and specific growth rate were significantly increased with the supplementation of NAC. Supplementation of NAC plus glycine significantly increased the feed efficiency. Glutathione peroxidase (GPx) and γ-glutamine cysteine synthase (γ-GCS) in plasma were significantly increased with the supplementation of NAC plus glycine. GSH in plasma increased and malondialdehyde (MDA) decreased in fish fed diets supplemented with NAC. Respiratory burst, superoxide dismutase (SOD), and catalase (CAT) activity were not affected by NAC or glycine. These results clearly indicated that NAC improved the growth performance and restored GSH of grass carp, supplemented NAC together with glycine enhanced GSH synthesis, and improved the antioxidative ability of grass carp.

Dietary taurine can improve the hypoxia-tolerance but not the growth performance in juvenile grass carp Ctenopharyngodon idellus.

This study was conducted to evaluate the effects of dietary taurine, as a feed additive, on the hypoxia-tolerance and growth performance of the juvenile grass carp Ctenopharyngodon idellus, one of the most important and intensively cultured freshwater fish, with the largest production in China. Graded levels of taurine (0, 0.5, 1, 1.5, 2 and 2.5 g kg(-1) dry diet) were fed to grass carp juveniles (mean weight: 5.26 ± 0.03 g) for 8 weeks. The survival time during acute hypoxia increased as dietary levels of taurine increased, with the highest dose of taurine resulting in the best acute hypoxia-tolerance. The erythrocyte osmotic fragility in grass carp was significantly improved when dietary taurine level was at least 1.5 g kg(-1) diet and can be improved much more when dietary taurine level was up to 2.5 g kg(-1) diet. A significant correlation between hemolysis rate of the erythrocyte osmotic fragility test and the survival time of acute hypoxia (r = -0.873, P = 0.023 < 0.05) strongly suggested that the biomembrane stabilization function of taurine may contribute to its role of enhancing acute hypoxia-tolerance in grass carp. Dietary taurine cannot improve growth performance of grass carp, but it can increase the value of mesenteric fat index, indicating that dietary taurine influences the lipid metabolism. This study provides valuable information to improve hypoxia-tolerance of grass carp.

Effect of dietary vitamin E and selenium supplementation on growth, body composition, and antioxidant defense mechanism in juvenile largemouth bass (Micropterus salmoides) fed oxidized fish oil.

Six oxidized fish oil contained diets were formulated to investigate the effect of graded levels of vitamin E (V(E)) (α-tocopherol acetate: 160, 280, and 400 mg kg(-1)) associated with either 1.2 or 1.8 mg kg(-1) selenium (Se) on growth, body composition, and antioxidant defense mechanism of juvenile largemouth bass. Another control diet containing fresh fish oil with 160 mg kg(-1) V(E) and 1.2 mg kg(-1) Se was also prepared. Over a 12-week feeding trial, about 5 % of Micropterus salmoide fed diet OxSe1.2/V(E)160 showed inflammation and hemorrhage symptoms at the base of dorsal, pectoral, and tail fin. Fish in all treatments survived well (above 90 %). Feed intakes (88.42-89.58 g fish(-1)) of all treatments were comparable. Growth performances (weight gain and specific growth rate) and feed utilization (feed and protein efficiency ratio) were significantly impaired by dietary oil oxidation, and they did not benefit from neither V(E) nor Se supplementation. Regardless of dietary V(E) and Se supplementation, oxidized oil ingestion resulted in markedly decreased hepatosomatic index and intraperitoneal fat ratio. Oxidized oil ingestion also induced markedly lower liver and muscle lipid contents, and these effects could be alleviated by dietary Se supplementation. Dietary oil oxidation stimulated hepatic catalase activities relative to the control, and supplementation of V(E) abrogated this effect. Hepatic reduced glutathione content in the control was markedly higher than that of treatment OxSe1.2/V(E)160, without any significant differences comparing with the other oxidized oil receiving groups. Hepatic glutathione peroxidase activity and liver Se concentration reflected dietary Se profile, whereas liver V(E) level reflected dietary V(E) profile. Compared with the control, fish fed diet OxSe1.2/V(E)160 obtained markedly higher serum, liver and muscle malondialdehyde contents, which droppe significantly with increasing either V(E) or Se supplementation. In conclusion, the overall results in this study suggested that both V(E) and Se inclusion could protect largemouth bass from the oxidative damage challenged by dietary oil oxidation.