Effects of dietary protein and lipid levels on growth, feed conversion and body composition in rohu, Labeo rohita (Hamilton), fingerlings

Twelve experimental diets (D-1 to D-12) in a 4 x 3 factorial design (four protein levels: 250, 350, 400 and 450 g kg(-1) and three lipid levels: 50, 100 and 150 g kg(-1) ) were formulated. Carbohydrate level was constant at 250 g kg(-1) . Rohu fingerlings (average wt. 4.3+/-0.02 g) were fed the experimental diets for 60 days in three replicates at 2% BW day(-1) . Weight gain (%), specific growth rate (% day(-1) ) and feed gain ratio (FGR) indicated that diets containing 450 g kg(-1) protein and 100 or 150 g kg(-1) lipid (diets D-11 and D-12) resulted in best performance, although results were not significantly different from those of diet D-9 (400 g kg(-1) protein and 150 g kg(-1) lipid). Protein efficiency ratio was highest with diets D-6 (350 g kg(-1) protein and 150 g kg(-1) lipid) and D-9 (400 g kg(-1) protein and 150 g kg(-1) lipid) (P>0.05) and declined with higher and lower protein diets at all levels of lipid tested. Elevated lipid level (50, 100 or 150 g kg(-1) ) did not produce better FGR in diets containing 400 and 450 g kg(-1) dietary protein (P>0.05). The combined effects of protein and lipid were evident up to 400 g kg(-1) protein. Growth and FGR showed consistent improvement with increased lipid levels from 50 to 150 g kg(-1) at each protein level tested except with diets containing 450 g kg(-1) protein. Apparent nutrient digestibility (for protein, lipid and energy) did not show significant variation among different dietary groups (P>0.05). Whole body protein and lipid contents increased significantly (P>0.05) with dietary protein level. The results of this study indicate that rohu fingerlings are adapted to utilize high protein in diets with varying efficiency. The fish could utilize lipid to spare protein but there is no significant advantage from this beyond the dietary protein level of 350-400 g kg(-1) in terms of growth and body composition.