饲料中脂肪与蛋白质比对大口黑鲈生长、体组成和非特异性免疫的影响

为探讨大口黑鲈饲料中不同脂肪与蛋白质含量比对其生长、体组成和非特异性免疫的影响,实验设计了8种(D1~D8)不同脂肪与蛋白质含量比的总能递增饲料。D1~D8饲料的脂肪水平递增(9.0%～26.5%),而蛋白质水平递减(52.0%～31.0%)。用上述饲料饲养体质量为(10.06±0.02)g的大口黑鲈88 d,每饲料设3重复,每重复30尾鱼。结果显示,特定生长率、饲料效率、蛋白质消化率、脂肪消化率和脂肪沉积率均以D2组最高,但随饲料中脂肪与蛋白质含量比的进一步升高呈现显著下降趋势。D3~D5组的蛋白质效率显著高于D1和D8组。D2、D3组与D4组间的蛋白质沉积率差异不显著,但显著高于其他各组。D1~D4组间的总能消化率差异不显著,但显著地高于其他各组。饲料中脂肪含量过高对鱼体组成产生显著的影响,使体脂的积蓄显著增高。随着饲料中脂肪与蛋白质含量比的升高,成活率呈显著下降趋势,D1和D2组的成活率显著高于D5~D8组。非特异性免疫分析显示,D4组血清溶菌酶活力和D2组血清补体活性及头肾白细胞呼吸爆发活性为最高。以饲料为单因子作单因素方差分析得出,满足大口黑鲈最适生长和饲料利用的饲料蛋白质和脂肪水平分别为49.30%和11.50%。以饲料中蛋白质和脂肪水平为自变量,分别以特定生长率和蛋白质沉积率为因变量进行二元二次回归分析得出,特定生长率最大时,饲料中蛋白质、脂肪和脂肪与蛋白质含量比分别为48.20%、12.44%和0.26;蛋白质沉积率最高时,饲料中蛋白质、脂肪和脂肪与蛋白质含量比分别为46.42%、13.96%和0.30。以饲料蛋能比为自变量作一元二次回归分析得出,蛋白质沉积率最大时,饲料的蛋能比、蛋白质、脂肪和脂肪与蛋白质含量比分别为23.72mg/kJ、46.16%、14.18%和0.31。研究认为,饲料的脂肪和蛋白质水平对大口黑鲈的生长、体组成、饲料效率和免疫力有着不同程度的影响;饲料中过高的脂肪会抑制蛋白质的消化与利用,表明脂肪对蛋白质的节约作用有限。建议大口黑鲈实用饲料的蛋白质和脂肪水平分别保持在46%~49%和11.5%~14%范围内较为适当。

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, CH50 and 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.