The Effect Of Dietary Phenylalanine Supplement On Growth, Flesh Quality Parameters, Antioxidant Capacity And Intestine Immune Function Of Young Grass Carp (Ctenopharyngodon Idellus)

This study investigated the effects of phenylalanine on growth, flesh quality parameters, antioxidant capacity and intestine immune function of young grass carp (Ctenopharyngodon idellus). A total of 540 young grass carp (255.9±1.2 g) were fed diets containing 3.4 (basal diet),6.1,9.1,11.5,14.0 and 16.8 g phenylalanine kg-1 diet with a fixed of 10.7 g tyrosine kg-1 diet for 8 weeks.The growth experiment showed percent weight gain (PWG), feed efficiency and feed intake of fish were the lowest in fish fed the basal diet (P<0.05). Muscle protein, lipid, shear force and hydroxyproline concentration were significantly improved by appropriate phenylalanine (.P<0.05). Cooking loss and cathepsin B and L activities exhibited an opposite tendency. Additionally, optimum phenylalanine significantly enhanced glutathione (GSH) content and the activities and gene expression of copper/zinc superoxide dismutase (SOD1), catalase (CAT) and glutathione peroxidase (GPx) in the muscle (P<0.05). Moreover, the expression levels of target of rapamycin (TOR), ribosome protein S6 kinase 1 (S6K1) and NF-E2-related factor 2 (Nrf2) in the muscle were significantly elevated by appropriate phenylalanine. Meanwhile, the results showed that phenylalanine enhanced lysozyme and acid phosphatase activities in the intestine (P<0.05). And phenylalanine increased mRNA levels of interleukin 10 (IL-10) and transforming growth factor β1 (TGF-β1) (P<0.05) and decreased tumor necrosis factor a and interleukin 8 gene expression (P<0.05), which was due to up-regulation of TOR and IκBα gene expression, and decreased the mRNA levels of NF-κB p65 (P<0.05). Moreover, phenylalanine enhanced tight junction claudinc, claudin3, claudinl5, occludin and ZO-1 gene expression (P<0.05). In addition, phenylalanine decreased malondialdehyde and protein carbonyl content in the intestine, which may partly due to phenylalanine increase SOD 1,CAT, GPx activities and GSH content(P<0.05). Furthermore, phenylalanine increased SOD1, CAT and GPx mRNA levels, which might be ascribed to the up-regulation of Nrf2 and down-regulation of Kelch-like-ECH-associated protein 1 (Keap1) expression in the intestine (P<0.05).In conclusion, phenylalanine improved the fish growth performance, flesh quality and muscle antioxidant capacity and regulated antioxidant-related signalling molecule expression. Meanwhile, phenylalanine improved the fish intestinal mucosal immune status and antioxidant defense, as well as regulated gene expression of antioxidant enzymes, TOR, Nrf2, Keap1 and NF-κB p65 in the intestine of grass carp. The phenylalanine requirement of young grass carp (256-629 g) based on PWG was 10.4 g kg-1 diet or 3.44 g 100 g-1 protein.