Optimal Dietary Vitamin B₂ And Vitamin B₁₂ Requirements Of Juvenile Blunt Snout Bream?Megalobrama Amblycephala?

This study aimed to investigate the optimum dietary vitamin B2 and vitamin B12 requirements of juvenile blunt snout bream(Megalobrama amblycephala)based on the results of growth performance,body composition,antioxidant capacity,intestinal digestive enzyme activities and the expressions of growth-related genes.The results obtained here could facilitate the development of artificial feed for this species.The experiment included two parts.Experiment 1 Optimal vitamin B2 requirement of juvenile blunt snout breamThis 12-week feeding trial aimed to investigate the optimum dietary vitamin B2 requirement of juvenile blunt snout bream(Megalobrama amblycephala)based on growth performance,body composition,antioxidant capacity and intestinal digestive enzyme activities.Fish were randomly divided into 6 groups,and were fed 6 semi-purified diets,containing various vitamin B2 levels(1.66,2.83,4.29,6.15,8.37 and 11.28 mg vitamin B2 kg-1 dry diet)respectively.Feed conversion ratio,survival rate,biometric parameters,whole-body moisture,protein and ash contents all showed no statistical difference among all the treatments(P>0.05).Weight gain rate,specific gain rate,body lipid contents and hepatic D-AAO activities all increased significantly(P<0.05)as dietary vitamin B2 ranged from 1.66 to 6.15 mg·kg-1,but all decreased with further increasing dietary vitamin B2 levels(P>0.05 for growth,P<0.05 for others).Liver vitamin B2 contents increased significantly(P<0.05)as dietary vitamin B2 increased from 1.66 to 8.37 mg·kg-1,but decreased with with further increasind dietary vitamin B2 levels(P<0.05).Activities of hepatic SOD,CAT and intestinal amylase,protease and lipase,as well as thecontents of liver GSH all increased significantly(P<0.05)as dietary vitamin B2 levels increased from 1.66 to 4.29 mg·kg-1.However,they all decreased significantly(P<0.05)with further increasing dietary vitamin B2 levels with the exception of MDA contents.Based on the broken-line regression analysis of weight gain rate,liver vitamin B2 contents and hepatic D-AAO activities,the optimal dietary vitamin B2 level for juvenile blunt snout bream was estimated to be 5.54 mg kg-1,4.65 mg·kg-1 and 6.02 mg·kg-1,respectively.Experiment 2 Optimal vitamin B12 requirement of blunt snout bream fingerlingsThis 12-week feeding trial aimed to investigate the optimum dietary vitamin B12 requirement of blunt snout bream(Megalobrama amblycephala)fingerlings based on growth performance,body composition,intestinal enzyme activities and relative gene expressions.Fish(0.71 ± 0.03 g)were randomly divided into 6 groups,and were fed 6 purified diets,containing various vitamin B,2 levels(0,0.025,0.05,0.1,0.2 and 0.4 mg vitamin B12 kg-1 dry diet)respectively.The results showed that survival rate,biometric parameters,whole-body compositions,activities of intestinal Na+-K+-ATP,AKP and y-GT all showed no statistical difference among all the treatments(P>0.05).Weight gain rate,specific gain rate,activities of intestinal amylase,protease,lipase and gene expressions of IGF-I all increased significantly(P<0.05)as dietary vitamin B12 ranged from 0 to 0.1 mg·kg-1,but all decreased with further increasing dietary vitamin B12 levels(P>0.05 for weight gain rate,specific gain rate and activities of intestinal protease,P<0.05 for others),While feed conversion ratio showed the opposite trend(P>0.05).The gene expressions of GH decreased significantly(P<0.05)among all the treatments.Based on broken-line regression analysis of weight gain rate against dietary vitamin B12 levels,the optimal dietary vitamin B12 level for blunt snout bream fingerlings was 0.061 mg· kg-1.In a word,based on broken-line regression analysis of weight gain rate,liver vitamin B2 contents and activities of hepatic D-AAO,the optimal dietary vitamin B2 level for juvenile blunt snout bream was 5.54 mg· kg.1,4.65 mg·kg-1 and 6.02 mg·kg-1,respectively.Optimal dietary vitamin B2 can enhance the antioxidant capacity and intestinal enzyme activities.Based on broken-line regression analysis of weight gain rate against dietary vitamin B12 levels,the optimal dietary vitamin B12 level for blunt snout bream fingerlings was 0.061 mg·kg-1,and optimal dietary vitamin B2 can increase intestinal enzyme activities and the gene expressions of IGF-I.