摘要This research evaluated the effects of copper(Cu)on intestinal antioxidant capacity and apical junctional complex(AJC)in juvenile grass carp.A total of 1080 healthy juvenile grass carp(11.16±0.01 g)were fed six diets including different dosages of Cu,namely 0,2,4,6,8 mg/kg(Cu citrate[CuCit]as Cu source)and 3 mg/kg(CuSO4-5H2O as Cu source).The trial lasted for 9 weeks.The findings revealed that dietary optimal Cu supplementation(2.2 to 4.1 mg/kg)promoted intestinal growth,including intestinal length,intestinal length index,intestinal weight,and intestinal somatic index(P＜0.05).Furthermore,optimal Cu boosted the intestinal mucosal barrier in juvenile grass carp.On the one hand,optimal Cu reduced diamine oxidase and D-lactate levels in serum(P＜0.05),reduced levels of the oxidative damage in-dicators malondialdehyde,reactive oxygen species(ROS),protein carbonyl,superoxide dismutase(P＜0.05),and catalase mRNA levels were elevated(P＜0.05),thus boosting intestinal antioxidant ca-pacity,the binding protein Keap1a/1b/Nrf2 signaling pathway might be involved.Optimal Cu had no impact on glutathione peroxidase 1b(GPx1b)gene expression(P＞0.05).On the other hand,optimal Cu increased intestinal tight junction(TJ)proteins(except for claudin 15b)and adherens junction(AJ)proteins(E-cadherin,α-catenin,β-catenin,nectin and afadin)mRNA levels(P＜0.05),which could be connected to the signaling pathway formed by the Ras homolog gene family,member A(RhoA),Rho-associated kinase(ROCK),and myosin light chain kinase(MLCK).Finally,based on serum indicator D-lactate and intestinal oxidative damage index(ROS),Cu requirement(CuCit as Cu source)for juvenile grass carp from initial weight to final weight(from 11 to 173 g)was determined to be 4.14 and 4.12 mg/kg diet,respectively.This work may provide a theoretical foundation for identifying putative Cu regulation pathways on fish intestinal health.