Effects Of Protein Levels On Growth Performance, Digestive Functions And Protein Metabolism Of Juvenile Jian Carp (Cyprinus Carpio Var. Jian)

This experiment was conducted to determine the effects of protein levels on growth performance,digestive functions and protein metabolism of juvenile Jian carp(Cyprinus carpio var.Jian).Brown fish meal was used as the sole protein source in the study.Six isoenergetic experimental diets containing approximately 14.4 MJ kg^-1 of digestible energy and 22.0%,27.5%,33.0%,38.5%,44.0%,49.5%crude protein were fed to triplicate groups of 50 fish with an average initial weight of 16.7±0.01g(Mean±SEM) for 45 days.Results indicated PWG(R²=0.914,P＜0.01),SGR(R²= 0.897,P＜0.01),TFI(R²=0.618, P＜0.01)and FE(R²=0.906,P＜0.01) were significantly affected by protein levels. Estimating by broken line model,PWG,SGR and FE plateaued when protein levels were higher than 34.1%,33.9%,34.7%,respectively.Correlation analysis revealed PWG significantly correlated with the enhancement of TFI and FE(r＝+0.921,P＜0.01;r= +0.988,P＜0.01),path analysis indicated TFI and FE acted directly with PWG(P_0.1=0.290, P＜0.01;P_0.2=0.742,P＜0.01).Hepatosomatic index,hepatosomatic protein content,relative intestinal length,intestinal protein content,condition factor,trypsin,chymotrpsin,lipase, amylase activity in the hepatopancreas and trypsin,chymotrpsin,amylase,CK,Na⁺, K⁺-ATPase,AKP,γ-GT activities in the intestine were found significantly responded to protein levels.Correlation analysis indicated the enhancement of digestive enzymes in the hepatopancreas and intestine significantly attributed to the increase of FE,which showed that strong relationship existed between FE and digestive enzymes in the hepatopancreas and intestine.NI(R²=0.992,P＜0.01),ANI(R²= 0.994,P＜0.01),GOT(R²=0.893,P＜0.01), GPT(R²=0.949,P＜0.01) and PAC(R²=0.934,P＜0.01)linely correlated with protein levels, on the contrary,PER(R²=0.912,P＜0.01) and PPV(R²=0.996,P＜0.01)were negatively correlated with protein levels,nitrogen retention was positivly correlated with protein levels(R²=0.927,P＜0.01),nitrogen retention was found negatively correlated with protein levels when protein level was higher than 33.8%(R²=0.462,P＜0.05).Results of the experiment indicated protein levels have a positivly protmotion to the growth performance,development of digestive organs,digestive enzymes and absorption of the intestine of junvenil Jian carp;Meanwhile,protein levels promoted the increase of activities of GOT,GPT and the increase of PAC.In considering these results,it was concluded that the 34.1%,35.1%,33.0%,33.8%protein in the diet provided maximum growth,maximum trypsin activities,maximum chymotrpsin activities,maximum nitrogen deposition,respectively,for Jian carp with the body weight range from 16.7 to 55.0 g under these experimental conditions.