Effects of dietary starch levels on growth performance,digestive enzyme activities and muscle composition of adult blunt snout bream (Megalobrama amblycephala)

A 9-week feeding trial was conducted to assess the effect of dietary starch level on growth performance,digestive enzyme activities and muscle composition of adult blunt snout breaminitial weight(161±2.7)g.Six isonitrogenous and isolipidic diets were formulated with increasing starch inclusion from 17.1 to 41.9%.At the end of the feeding trial,survival rate and specific growth rate were not affected by dietary starch level.Feed efficiency rate(FER)and protein efficiency ratio(PER)were enhanced by increasing dietary starch supplementation.Dietary starch levels did not affect total protease activities in the liver and intestine,while up-regulated amylase activities.Cellulase activities were detected in the intestine and there were no significant differences among treatments.Hepatosomatic index,liver glycogen and muscle crude lipid contents were significantly increased with the increasing dietary starch levels.Similar serum glucose,total cholesterol and triglyceride contents were observed among the treatments.However significantly lower serum complement 3 and 4 contents were observed in fish fed the highest starch diet(41.9%)compared with those fed with 17.1 or 21.8% starch diets.In conclusion,the 41.9% dietary starch level gave no negative effect on growth of adult blunt snout bream,and considering the serum complement activities,the dietary starch level should not exceed 36.3% for adult blunt snout bream.On the basis of PER and FER,the optimum dietary starch requirement of adult M.amblycephala was estimated to be 34.1% of diet and 31.4% of diet,respectively,using broken-line regression analysis.