This study was conducted to examine the effects of dietary valine on the physical and flavor characteristics,fatty acid(FA)profile,antioxidant status and Nrf2-dependent antioxidant enzyme gene expression in the muscle of young grass carp(Ctenopharyngodon idella)fed increasing levels of valine(4.3,8.0,10.6,13.1,16.9 and 19.1 g/kg)for 8 weeks.Compared with the control group,the group fed valine showed improved physical characteristics of fish fillets(increased relative shear force,hydroxyproline,protein and lipid levels and decreased cathepsin B and L activities,as well as cooking loss,were observed).Moreover,valine improved the flavor of young grass carp fillets by increasing the amino acid(AA)concentration in fish muscle(increased aspartic acid,threonine,glutamine,cystine,methionine,leucine,tyrosine,phenylalanine,lysine,histidine,arginine and valine concentrations were observed).Additionally,optimal valine supplementation increased the potential health benefits to humans by decreasing the saturated FA(C15:0 and C16:0)concentration and increasing the unsaturated FA(monounsaturated FAs(MUFAs),such as C16:1,C18:1c+t and C20:1,and polyunsaturated FAs(PUFAs),such as C18:3n-3,C20:2 and C22:6)concentration.In addition,the reduced glutathione(GSH)content and the activities of Cu/Zn superoxide dismutase(SOD1),catalase(CAT)and Selenium-dependent glutathione peroxydase(Se-GPx)increased under valine supplementation(P < 0.05).Furthermore,the SOD1,CAT and Se-GPx mRNA levels increased with dietary valine levels,possibly due to the up-regulation of NF-E2-related factor 2(Nrf2),target of rapamycin(TOR)and ribosomal protein S6 kinase 1(S6K1)and the down-regulation of Kelch-like-ECH-associated protein 1(Keap1)in muscle(P < 0.05).In conclusion,valine improved the physical and flavor characteristics,FA profile,and antioxidant status and regulated the expression of the antioxidant enzyme genes Nrf2,Keap1,TOR and S6K1 in fish fillets.