Abstract: A three component mixture design(cornell design)was used to investigate the optimal composition of macronutrients including protein from 33%to 51%,fat from 3%to 18%and carbonhydrate from 24%to 33%in dry weight for juvenile longsnout catfish Leiocassis longirostris Gunther with initial body weight of(2.0±0.1)g.A total of 1 920 test fish were randomly stocked into 64 cages displaced in an indoor tank with a tiny running water system at a rate of 30 individuals per cage.In the 60 cages,the fish were fed 20 diets with triplication,and 1 group diet with tetraplication for 60 days.The results showed that no significant effect of the dietary macronutrient composition on fish survival was observed except for the significant decline at 33%dietary protein(P＜0.05). There was a positive effect of increasing dietary protein levels on the growth at the dietary protein level of over 48%,while dietary protein levels from 33%to 36%resulted in growth depression significantly(P＜0.05).Besides dietary lipid 6%,the fish fed the diet containing lipid 9%showed significantly better growth than the fish fed the diet containing other lipid levels(P＜0.05).There was significantly higher lipid contents in body or liver of the fish fed the diet containing lipid level of over 15%(P＜0.05).There was no significant effect of dietary carbohydrate levels on the growth of the fish(P＞0.05),and the glycogen contents were found to be increased in whole body and liver of the fish fed the diet containing carbohydrate level of 33%(P＜0.05).It can be concluded that the optimal dietary macronutrient requirement appears to be protein 45%,carbohydrate 30%,lipids 9%,and gross energy 20.0 MJ/kg.
2013, Vol. 28 
