Effects of Dietary Protein to Energy Ratio on Growth Performance and Digestive Enzyme Activities of Juvenile Topmouth Culter, Culter alburnus

This experiment was conducted to study the effects of dietary protein to energy ratio(P/E) on growth performance and digestive enzyme activities of juvenile topmouth culter,Culter alburnus.Nine experimental diets with different dietary P/E were formulated to contain 3 protein levels(45%,40% and 35%) and 3 lipid levels(5%,8% and 11%).A total of 810 juvenile topmouth culter with an initial average body weight of(10.14±3.40) g were randomly divided into 9 groups with 3 replicates per group and 30 fish per replicate.Fish in the 9 groups were fed the experimental diets with 30.94(protein/lipid=45%/5%,D1),29.73(protein/lipid=40%/5%,D2),28.11(protein/lipid=35%/5%,D3),29.03(protein/lipid=45%/8%,D4),27.79(protein/lipid=40%/8%,D5),26.32(protein/lipid=35%/8%,D6),26.90(protein/lipid=45%/11%,D7),25.71(protein/lipid=40%/11%,D8) and 23.50 g/MJ(protein/lipid=35%/11%,D9) for 8 weeks,respectively.The results showed as follows: dietary P/E significantly affected the weight gain rate(WGR),specific growth rate(SRG),hepatopancreas somatic index(HSI) and intraperitoneal fat ratio(IPR)(P0.05),and the maximum of WGR and SGR were all found in group D5,but showed no significant difference compared with groups D4,D6 and D7 in SRG(P0.05).Dietary P/E significantly affected the protease activity in intestine and hepatopancreas(P0.05),and both of them were firstly increased and then decreased with the increase of dietary P/E.The intestinal protease activity in group D4 had the highest value,and was significantly higher than that in other groups(P0.05);the hepatopancreas protease activity in group D7 had the highest value,but showed no significant difference compared with groups D4,D5 and D6(P0.05).Dietary P/E significantly affected the lipase activity in intestine and hepatopancreas(P0.05),but the regularity of variations was not so obvious with dietary P/E change.Dietary P/E showed no significant effect on amylase activity in both intestine and hepatopancreas(P0.05).Through the analysis of growth performance and digestive enzyme activities,it is concluded that the optimum dietary P/E of juvenile topmouth culter is 26.90 to 29.03 g/MJ,and the requirement of dietary P/E for maximum SGR is 27.15 g/MJ,which is determined by the quadratic model regression equation.Considering about the growth performance and protein-spare effect of juvenile topmouth culter,we suggest the dietary protein and lipid levels are 40% and 8% under the optimum dietary P/E,respectively.