Effects of dietary lipid to protein ratios on growth performance,body composition and non-specific immunity of largemouth bass (Micropterus salmoides)

An 88-day feeding test was conducted to estimate the effects of dietary lipid to protein ratios on growth performance,body composition and non-specific immunity in largemouth bass with initial body weight(10.06±0.02) g.Eight diets(D1-D8)were formulated with varying lipid to protein(LIP/PRO,w/w) ratios ranging from 0.17 to 0.84.From D1 to D8,dietary lipid levels were increased(9.0%-26.5%),while dietary protein levels were decreased(52.0%-31.0%).The results of this study suggested that the specific growth rate,feed efficiency ratio(FER),dietary protein digestibility coefficient,dietary lipid digestibility coefficient and lipid deposition of D2-fed fish were the highest.The protein efficiency ratio was significantly higher in fish fed D3-D5,compared with fish fed D1 and D8.The protein deposition rates of D2-and D3-fed fish were significantly higher than those in fish fed D1 and D5-D8.The dietary energy digestibility coefficients among the fish fed D1-D4 were significantly higher than those with other treatments.Excessive dietary lipid had a significant effect on body composition with increased body lipid deposition.The survival rates were significantly higher in fish fed D1 and D2 with higher protein levels,compared with those in fish fed D5-D8 with lower protein levels.The highest activity of lysozyme,CH50and respiratory burst of head kidney leukocytes occurred in D4-,D2-and D2-fed fish,respectively.According to a one-way ANOVA against dietary treatment,the optimal dietary protein and lipid levels for growth and FER of largemouth bass are 49.30% and 11.50%,respectively.Using a second-order polynomial regression analysis,the optimum dietary protein,lipid and lipid to protein ratio(L/P) in the diet for largemouth bass are estimated,based on the specific growth rate(SGR) and protein deposition rate(PDR).With the highest SGR,the optimum dietary protein,lipid and L/P are estimated to be 48.20%,12.44% and 0.26.With the highest PDR,the optimum dietary protein,lipid and L/P are estimated to be 46.42%,13.96% and 0.30.A quadratic regression analysis of PDR against dietary protein to energy ratio(P/E) indicates a similar result that the optimum dietary P/E,protein,lipid and L/P requirements of largemouth bass are 23.72 mg/KJ,46.16%,14.18% and 0.31,respectively.Based on those results,it could be concluded that largemouth bass growth performance,body composition and non-specific immunity are affected by dietary lipid and protein levels to different extents,and that an excess of dietary lipid inhibits digestion of dietary protein,suggesting that protein-sparing effect of dietary lipid is limited in this fish species.It could be recommended to maintain dietary protein and lipid levels within 46%-49%,and 11.5%-14%,respectively,in the practical feed for largemouth bass.