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In this study, fish were fed six diets containing different levels of pyridoxine (PN) for 10 weeks, and then infected with Aeromonas hydrophila for 2 weeks. The results showed that dietary supplementation with PN had a powerful effect on the inhibition of skin haemorrhage and lesion morbidity, and the enhancement of immunity after fish were infected with A. hydrophila. For example, PN increased the levels of immunoglobulin M (IgM), acid phosphatase (ACP), complement 3 (C3), lysozyme (LZ), C4, antimicrobial peptides, target of rapamycin (TOR), anti‐inflammatory cytokines, ribosomal protein S6 kinases 1 (S6K1) and inhibitor of κBα (IκBα), while decreasing the levels of proinflammatory cytokines [except interleukin‐12 p40 (IL‐12p40)], eIF4E‐binding proteins (4E‐BP), IκB kinase β (IKKβ) and nuclear factor κB p65 (NF‐κBp65) in grass carp skin. Additionally, dietary supplementation with PN increased the levels of tight junction proteins (not claudin‐15 and claudin‐12), antioxidant enzymes [except manganese superoxide dismutase (MnSOD) activity and gene expression, glutathione peroxidase 4a (GPx4a) and GPx4b gene expression], NF‐E2‐related Factor 2 (Nrf2), myeloid cell leukaemia‐1 (Mcl‐1) and inhibitor of apoptosis proteins (IAP), while decreasing the levels of malondialdehyde (MDA), reactive oxygen species (ROS), protein carbonyl (PC), Kelch‐like ECH‐associating protein 1a (Keap1a) myosin light chain kinase (MLCK), cysteinyl aspartic acid protease‐9 (caspase‐9), caspase‐8, caspase‐7, caspase‐3, Bcl‐2‐associated X protein (Bax), p38 mitogen‐activated protein kinase (p38MAPK) and apoptotic protease‐activating factor 1 (Apaf‐1) in grass carp skin. In summary, dietary PN can enhance the immunity of fish skin via elevated immune substances, an eased inflammatory response and an improved barrier integrity. [ABSTRACT FROM AUTHOR]

To study the effects of manganese on growth performance, digestive and absorptive abilities, as well as the antioxidative capacity in the hepatopancreas and intestine, young grass carp ( Ctenopharyngodon idellus Val.) (264 ± 1 g) were fed diets containing graded levels of manganese at 3.65 (control), 8.62, 13.48, 18.24, 22.97 and 27.86 mg kg−1 diet for 8 weeks. Per cent weight gain ( PWG) and feed intake were the poorest in fish fed the basal diet ( P < 0.05). The activities of trypsin, lipase and alkaline phosphatase in the intestine were significantly enhanced with dietary manganese level at 13.48 mg kg−1 diet ( P < 0.05). Additionally, in the hepatopancreas and intestine, the protein carbonyl and malondialdehyde contents were the lowest in fish fed the diet with dietary manganese level at 13.48 mg kg−1 diet ( P < 0.05), while the anti-hydroxyl radical capacities, manganese superoxide dismutase (Mn SOD), glutathione peroxidase and glutathione- S-transferase activities were significantly enhanced with dietary manganese level at 13.48 mg kg−1 diet ( P < 0.05). Moreover, the catalase activity and glutathione content in the intestine were the highest in fish fed the diet with dietary manganese level at 18.24 mg kg−1 diet ( P < 0.05). These results indicated that optimum dietary manganese promoted growth, enhanced the digestive and absorptive abilities, and improved the antioxidative capacity in young grass carp. Based on the quadratic regression analysis for PWG and intestinal Mn SOD activity, the manganese requirements for young grass carp with the initial body weight of 264 g were 16.91 and 18.21 mg kg−1 diet respectively. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate graded levels of dietary zinc on the growth, flesh quality, and the relationship between flesh quality and muscle antioxidant status in young grass carp ( Ctenopharyngodon idella Val.). Per cent weight gain ( PWG), special growth rate ( SGR), feed intake ( FI), feed conversion ratio ( FCR), anti-hydroxy radical ( AHR), superoxide dismutase ( SOD), catalase ( CAT), glutathione reducase ( GR) activities and glutathione ( GSH) content were significantly increased with increasing levels of Zn up to a point, and thereafter declined ( P < 0.05). Serum zinc, alkaline phosphatase ( AKP), muscle anti-superoxide anion ( ASA), glutathione peroxidase ( GPx), glutathione- S-transferase ( GST) activities and collagen content were significantly enhanced with dietary zinc levels up to a point ( P < 0.05), beyond which it plateaued. Cooking loss, shear force and malondialdehyde ( MDA) were significantly reduced with increasing level of zinc up to a point, and thereafter increased ( P < 0.05). The pH value significantly increased with the increasing zinc levels, whereas the trend of protein carbonyl content was opposite. Flesh quality was positively related to the antioxidant enzymes activities in muscle of young grass carp. These results indicated that optimum zinc could improve growth, and improve flesh quality partly through improving muscle antioxidant status of young grass carp. [ABSTRACT FROM AUTHOR]

This study was conducted to evaluate the effects of dietary myo-inositol (MI) on the antioxidant status of juvenile Jian carp ( Cyprinus carpio var. Jian). A total of 1050 Jian carp (22.28±0.07 g) were randomly distributed into seven groups of three replicates each, feeding diets containing graded levels of MI (163.5, 232.7, 384.2, 535.8, 687.3, 838.8 and 990.3 mg kg−1 diet) for 60 days. Results indicated that the malondialdehyde content was the lowest for fish fed diets containing ≥384.2 mg MI kg−1, and the highest for fish fed the MI-unsupplemented basal diet ( P<0.05). The protein carbonyl content was decreased with increasing dietary MI levels up to 535.8 mg kg−1 diet, and no differences were found with a further increase in the MI concentration. The anti-superoxide anion capacity (ASA) and anti-hydroxyl radical capacity (AHR) were increased with increasing MI levels up to 535.8 mg kg−1 diet, and plateaued thereafter. The superoxide dismutase and glutathione- S-transferase activities showed the same tendency with the ASA capacity. Catalase, glutathione peroxidase and glutathione reducase activities were improved with increasing MI levels up to 838.8, 384.2 and 687.3 mg kg−1 diet, respectively, and remained nearly constant thereafter. These results suggested that MI could inhibit oxygen radical generation, increase enzymatic antioxidant capacity and prevent oxidative damage of carp. Dietary MI requirements for ASA and AHR activities of juvenile Jian carp were 567.94 and 517.22 mg MI kg−1 diet respectively. [ABSTRACT FROM AUTHOR]