The Effect Of Dietary Arginine Supplement On Flesh Quality And Cu-induced Gill Barrier Function Of Young Grass Carp(Ctenopharyngodon Idellus)

A total of 540 young grass carp (Ctenopharyngodon idella) (278.82 ± 0.68 g) were fed graded levels of arginine (Arg) (6.9,10.4,14.1,17.6,21.4 and 24.5 g kg-1 diet) for 8 weeks to investigate the effects of dietary Arg on growth, antioxidant status and flesh quatily. After 8 weeks feeding trial,30 fish with similar weight were randomly selected from each treatment to conduct a challenge trial with 0.7 mg kg-1 CUSO4 exposure for 96 hours to investigate the effects of dietary Arg on Cu-induced gill barrier function damage.The growth trial results showed that weight gain, specific growth rate, feed intake, feed efficiency and protein efficiency ratio were significantly improved by dietary Arg (P < 0.05). Muscle protein and lipid content were increased by dietary Arg (P< 0.05), whereas muscle moisture and ash content followed an opposite trend (P< 0.05). Diet with optimal Arg can elevated muscle shear force, pH (Oh and 24h) value and hydroxyproline content, decrease the flesh cooking loss (P<0.05). Muscle protein carbonyl and malondialdehyde contents were significantly decreased with dietary Arg supplementation (P<0.05), while muscle anti-superoxide anion, anti-hydroxyl radical and glutathione content were significantly increased (P<0.05). The activities and gene expression of copper/zinc superoxide dismutase (SOD1), glutathione peroxidase (GPx) and catalase (CAT) in muscle were generally higher in fish fed with appropriate Arg-supplemented diet than unsupplement diet(P< 0.05). Moreover, the expressions of target of rapamycin (TOR), ribosome protein S6 kinase 1 (S6K1) and NF-E2-related factor 2 (Nrf2) in muscle were significantly elevated by appropriate arginine (P<0.05). However, optimum arginine significantly decreased Kelch-like-ECH-associated protein 1 (Keap1) mRNA level(P< 0.05).The Cu exposuer trial results showed that optimum Arg decreased Cu-induced grass carp gill protein oxidation and lipid peroxidation. Meanwhile, Arg inhibited Cu-induced gill antioxidant enzyme SOD1, GPx, GST and GR activities decreased (P< 0.05), while Cu could induced CAT activity increased and further increased with Arg supplementation (P< 0.05). Furthermore, Arg up-regulated SOD1, CAT, GPx, GR and GST gene expression (P< 0.05). Signaling molecules Nrf2 mRNA levels was up-regulated by Arg and Keapl expression was down-regulated (P< 0.05). Meanwhile, tight junction (TJ) proteins occludin, zonula occludens-1 (ZO-1), claudin b, claudin 3 and claudin 12 were increased by arginine in the gill (P< 0.05), whereas claudin 15 followed an opposite trend (P< 0.05), while Arg had no significant effect on the mRNA levels of claudin c (P>0.05). Arginine increased Cu-induced interleukin 10 (IL-10) expression (P< 0.05), and decreased tumor necrosis factor α (TNF-α), interleukin 1 (IL-1) and interleukin 8 (IL-8) genes expression (P<0.05) in gill, which was partly due to down-regulation of nuclear transcription factor-kB (NF-κB) and up-regulation of inhibitor factor κBα (IκBα) (P< 0.05). In addition, Arg inhibited Cu-induced TOR and S6K1 gene expression down-regulated (P< 0.05).In conclusion, dietary appropriate Arg could improve grass carp growth performance, and the dietary available Arg requirement of young grass carp archived perfect growth performance estimated by the broken-line regression analysis was 13.45 g kg-1 diet. Arginine improved flesh quality through enhancement muscle antioxidant capacity and regulation of antioxidant-related signaling molecules expressions. Arg could protect against Cu-induced gill barrier function damage through increment gill antioxidant capacity and gill epithelial TJ proteins expression, which partly related to Nrf2 and NF-κB pathway.