Effects of dietary protein and lipid levels in practical diets on growth performance and body composition of blunt snout bream (Megalobrama amblycephala) fingerlings

A feeding trial including diets with three protein levels (27%, 31% and 35%) and three lipid levels (4%, 7% and 10%) was conducted to investigate the optimum protein and lipid requirements of blunt snout bream fingerlings (average initial weight:1.76 ± 0.04 g). Fish were randomly distributed into 27 floating cages (2 × 1 × 1 m) and fed three times daily (06:30, 11:30 and 16:30 h) for 8 weeks. Weight gain generally improved with increasing protein levels, but no significant difference was observed. Weight gain of fish fed 7% lipid was significantly (P < 0.01) higher than that of the other groups. Feed conversion ratio improved significantly (P < 0.05) as protein level decreased from 35% to 31% and lipid level increased from 4% to 7% and 10%. Survival, hepatosomatic index and protein efficiency ratio decreased significantly (P < 0.05) with increasing protein levels. Nitrogen retention increased significantly as protein levels (P < 0.01) decreased and lipid levels (P < 0.05) increased. Contrary to moisture content, lipid content of whole-body and carcass increased significantly (P < 0.05) with increasing lipid levels; whereas, viscera composition showed a complex trend. Interaction of protein and lipid was only observed in viscera composition. The results of this study indicated that an increase in the dietary lipid level from 4% to 7% had a protein-sparing effect, and the diet containing 31% protein with 7% lipid (18.57 MJ/kg diet) is optimal for growth and effective protein utilization of blunt snout bream fingerlings.