Abstract:The present study was conducted to analyze the effects of dietary nucleotides on growth performance, intestinal morphology and anti-oxidative capacities of juvenile large yellow croaker(Larimichthys crocea)[initial weight:(7.71±0.02)g].Two control diets were set, which were high fish meal(FM, 45.0%)supplemented diet and low fish meal(N0, 31.5%)supplemented diet, respectively.Based on the latter, five graded levels of nucleotides were added.They were 75, 150, 300, 600 and 1 000 mg/kg, respectively.After the 9-week growth trial, results showed that survival rate, feed efficiency, feed intake and body composition of the animals were not significantly influenced by dietary nucleotides levels(P>0.05).Weight gain rates(WGR)of fish fed the diets with 300 or 600 mg/kg of nucleotides were significantly higher than those in the other groups(P<0.05).Dietary nucleotides significantly affected the total anti-oxidative capacity(T-AOC)and superoxide dismutase(SOD)activity in serum(P<0.05).Values of T-AOC and SOD increased first, and then declined as the dietary nucleotides levels increased.The highest values of these two parameters were found in the treatment with 300 mg/kg of dietary nucleotides.Dietary nucleotide significantly increased microvillus height(HMV)and the thickness of the muscular layer(TML)in the proximal intestine(P<0.05).The HMV in intestine of fish fed diet with 300 mg/kg of nucleotides was higher than that in the control group.The TML in intestine of fish fed diet with 150 mg/kg of nucleotides was higher than that in the control group.There was no significant difference in fold height(HF)of intestines among all groups(P>0.05).In conclusion, dietary nucleotides can improve the growth of the large yellow croaker.Meanwhile, it can also increase the anti-oxidative capacity and improve the intestinal morphology.Based on the data of WGR, the broken-line analysis showed that the optimal level of dietary nucleotides was 194.91 mg/kg.