A STUDY ON THE PROPER PROTEIN AND LIPID LEVELS IN THE DIET OF SALMO TRUTTA JUVENILES

This study was conducted to evaluate the effects of dietary protein and lipid levels on the growth performance, body composition, liver biochemical index and intestinal enzyme activity of juvenile brown trout. The experiment used a 3×2 two-factor design with protein levels of 42%, 46%, and 50% (P42, P46, and P50) and lipid levels of 12% and 16% (L12, and L16). Brown trout with an average initial weight of (2.80±0.10) g were randomly distributed into six groups with three fish per group and fed with one of the six diets for 56d. The results indicated that the P46L12 group had the highest weight gain (110.34%) and the lowest feed coefficient ratio (1.30), while the P50L16 group showed the lowest growth. There was no significant difference in the viscerosomatic index among all groups (P>0.05). The hepatosomatic index decreased with increasing dietary protein and fat levels. With the increase of dietary protein levels, the protein retention and lipid retention first increased and then decreased. Dietary lipid levels significantly affected the activity of intestinal protease, pepsin and gastric amylase activity (P<0.05), while dietary protein levels only affected pepsin activity (P<0.05). The P46L12 group had the highest protease and amylase activities in the stomach and intestine among those of all groups. At the same fat level, glutamic-pyruvic transaminase (GPT) activity and total cholesterol (TC) and triglyceride (TG) contents first increased and then decreased with increasing dietary protein levels. The above results indicated that the proper levels of crude protein and crude lipid in the diet of juvenile brown trout were 46% and 12%, respectively.