Effects of Dietary Lipid Levels on Growth Performance,Intestinal Digestive Enzyme Activities and Lipid Metabolism of Chinese Sucker(Myxocyprinus asiaticus)

Five hundred and forty Chinese sucker(Myxocyprinus asiaticus)with average body weight of(6.73±0.21)g were randomly divided into 6 treatments with 3 replicates in each treatment and 30 fish in each replicate to investigate the effects of dietary lipid levels on growth performance,intestinal digestive enzyme activities and lipid metabolism of Chinese sucker by feeding diets with six lipid levels(2.04%,4.43%,6.88%,9.02%,11.98% and 13.39%).After a 56-day feeding trial,the results showed as follows:dietary lipid levels had significant effect on the growth performance of Chinese sucker(P0.05).At the 6.88% level,the weight gain rate,special gain rate and RNA to DNA ratio reached the maximum,while the feed conversation ratio got the minimum.According to the second-order regression,the optimal dietary lipid level of Chinese sucker had the extremum of weight gain rate and feed conversation ratio was 6.62% and 7.02%,respectively,and the optimal energy to protein ratio was 45.77 and 45.96 kJ/g,respectively.Dietary lipid levels had significant effect on the intestinal digestive enzyme activities of Chinese sucker(P0.05).With the increase of dietary lipid levels,the protease activity was decreased,and the lipase activity was increased at first and then maintained at a steady state,while the amylase activity was decreased at first and then maintained at a steady state.Dietary lipid levels had significant effect on the lipid metabolism of Chinese sucker(P0.05).With the increase of dietary lipid levels,contents of total lipid,triglyceride and total cholesterol in serum were increased and activities of malate dehydrogenase in hepatopancreas and lipoprotein lipase in serum were decreased.In conclusion,the optimal dietary lipid level of juvenile Chinese sucker was 6.62%～7.02%,and the optimal energy to protein ratio was 45.77～45.96 kJ/g.Protease and amylase activities were negatively correlated with high dietary lipid levels.Serum lipid level was increased and enzyme activities for lipogenic and lipolysis function were decreased with the increasing of dietary lipid levels.