EFFECTS OF DIFFERENT PROTEIN AND LIPID LEVELS ON THE GROWTH PERFORMANCE AND BODY COMPOSITION OF BLUNT SNOUT BREAM (MEGALOBRAMA AMBLYCEPHALA) YEARLINGS

A 3×3 factorial design was used to determine effect of dietary protein and lipid levels on growth performance and body composition of blunt snout bream yearlings(average initial weight of 50.37±1.27 g).Nine experimental diets were formulated to contain three protein levels(25%,30% and 35%),each of which had three lipid levels(3%,6% and 9%).Fish were held in floating cages(2 m×1 m×1 m) and fed three times daily for 8 weeks.No interaction between dietary protein and lipid existed for growth performance and body composition(P0.05).No significant difference(P0.05) was observed in survival rate among all the treatments.Weight gain(WG),specific growth rate(SGR) and feed conversion ratio(FCR) were significantly influenced by both dietary protein(P0.05) and lipid levels(P0.05).WG and SGR of fish fed with 25% protein were significantly(P0.05) lower than that of the other groups;whereas,the opposite was true for fish fed with 6% lipid(P0.01).Although the lowest FCR was found in fish fed with 35% protein and 6% lipid,no significant difference(P0.05) was observed among the other treatments except for that of fish fed with 25% protein + 3% lipid and 25% protein + 9% lipid.Protein efficiency ratio(PER) and nitrogen retention efficiency decreased significantly with increasing dietary protein levels(P0.05).In addition,PER was significantly(P0.05) affected by dietary lipid level with the highest observed in fish fed with 6% lipid.Energy retention efficiency increased significantly as dietary lipid levels increased(P0.05).Condition factor improved significantly(P0.05) as dietary protein and lipid levels both increased.Intraperitoneal fat ratio and hepatosomatic index increased significantly(P0.05) as dietary lipid levels increased.No significant difference(P0.05) was observed in body composition among all the treatments at different dietary protein levels.Moisture,lipid and energy contents of whole-body were significantly(P0.01) affected by dietary lipid levels.Contrary to moisture content,lipid and energy contents of whole-body in-creased significantly(P0.01) with increasing lipid level.Similar results were also observed in carcass and liver composition.The results of this study indicated that diet containing 30% protein and 6% lipid with a protein to energy ratio of 18.21 g/MJ was suitable for blunt snout bream yearlings.