Abstract:A feeding trial was conducted to evaluate the optimum ratio at which dietary sodium dihydrogen phosphate(NaH2PO4)was replaced with citric acid in the diets of juvenile yellow catfish Pelteobagrus fulvidraco.Seven diets were formulated:positive control group(DP)that contained only 2% NaH2PO4 and negative control group(DN)that consisted of neither NaH2PO4 nor phytase;and five treatment groups supplemented with 2 g/kg citric acid and 20,15,10,5,0 g/kg concentrations of NaH2PO4.Thus,dietary NaH2PO4 was replaced with citric acid at ratios of 0%,25%,50%,75%,and 100%,respectively.The groups were desjgnated as D0,D25,D50,D75,and D100.Triplicate tanks were each filled with 50 juvenile ind.(3.5±0.1)g,which were fed with one of the seven experimental diets.After eight weeks,growth performance,apparent digestibility,body proximate composition,vertebra minerals and antioxidative capacity were investigated.The results showed that:(1)Citric acid supplementation enhanced weight gain and specific growth rate,reduced the feed conversion ratio compared with the negative group,but there were no significant differences with the positive group.;(2)Citric acid supplementation significantly enhanced the apparent digestibility of dry matter,protein and phosphorus and decreased fecal phosphorus and nitrogen content compared with negative group,while no significant difference with the positive group.The content of fecal nutrients decreased with the increasing of replacing level;(3)there were no differences among control groups and treatment groups in body moisture,crude protein,crude lipid and ash(P>0.05).Compared with the negative control,citric acid supplementation significantly improved the retention of Ca,Mg,P and Cu in the whole body.The highest retention of these nutrients was observed between 25% and 75% replacement levels.(4)Antioxidant enzymes activity(CAT,AKP and SOD)reached the highest between 25% and 75% replacement levels compared with the negative group while no differences were observed in serum MDA and IgM content.In conclusion,in order to reduce nitrogen and phosphorus output in the aquaculture water bodies,the replacing level of sodium dihydrogen phosphate with citric acid in yellow catfish diet between 25% and 50% will not affect fish growth performance and will help to improve nutrients utilization under the current conditions.