饲料中糖/脂肪比对暗纹东方幼鱼生长、血液指标、肝代谢酶活性及PEPCK基因表达的影响

Effect of dietary carbohydrate-to-lipid ratio on growth,blood biochemical indices,hepatic metabolic enzymes and PEPCK gene expression of juvenile obscure puffer( Takifugu obscurus)

配制6种不同糖/脂肪比例（CHO∶L分别为4.29、2.79、1.86、1.19、0.73和0.42）的等氮等能饲料,饲养暗纹东方鲀幼鱼[初始体质量为（11.2±0.5）g]60 d,探讨饲料中糖与脂肪比例对其生长、饲料利用、生理生化指标和PEPCK基因表达的影响。实验结果表明：随饲料中CHO∶L降低,暗纹东方鲀特定生长率（SGR）、蛋白质效率（PER）和饲料效率（FE）先升高后降低,且均在CHO∶L为1.86时达最大,显著高于CHO∶L为0.42、0.73和4.29时的值（P〈0.05）。血浆甘油三酯和肝脏脂肪含量随CHO∶L降低而显著增加（P〈0.05）,而血糖和肝糖原含量随CHO∶L降低而显著降低（P〈0.05）。随饲料中CHO∶L降低,肝脏脂肪酶和脂肪合成酶活性先增加后降低,分别在CHO∶L为1.19和1.86时活性最高。CHO∶L为1.86~4.29时丙酮酸激酶活性显著高于其他饲料组（P〈0.05）。CHO∶L为0.42和0.73时,淀粉酶活性显著低于其他饲料组（P〈0.05）,而PEPCK活性和mRNA相对表达量显著高于其他饲料组（P〈0.05）。饲料中CHO∶L对暗纹东方存活率和血浆总胆固醇含量无显著影响（P〉0.05）。分别用二次多项回归模型拟合SGR、PER、FE和CHO∶L的关系,得到暗纹东方幼鱼饲料中CHO∶L的适宜范围为2.01~2.16,且其对碳水化合物的利用能力要高于脂肪。

This experiment was conducted to evaluate the effects of dietary carbohydrate-to-lipid ratio on growth performance,feed utilization,biochemical indices and phosphoenolpyruvate carboxykinase（ PEPCK）gene expression in juvenile obscure puffer,Takifugu obscurus. Six isonitrogenous and isoenergetic diets were formulated with dietary CHO∶ L ratios of 4. 29,2. 79,1. 86,1. 19,0. 73 and 0. 42,respectively. Fish（ initial weight 11. 2 ± 0. 5 g） were stocked in triplicate tanks（ 25 fish per tank） and fed to satiation during a period of60 days. The results indicated that best specific growth rate,protein efficiency ratio and feed efficiency were found in fish fed diet with CHO∶ L of 1. 86,which were significantly higher than those of fish fed diets with0. 42,0. 73 and 4. 29（ P 〈 0. 05）. Plasma triglyceride and liver lipid content increased significantly as dietary CHO∶ L ratio decreasing（ P 〈 0. 05）,while plasma glucose and hepatic glycogen content showed a contrary tendency. Activities of lipase,fatty acid synthase,amylase and pyruvate kinase in liver were significantly affected by dietary CHO∶ L ratio（ P 〈 0. 05）. Fish fed diets with CHO∶ L of 0. 42 and 0. 73 had significantly higher PEPCK activity and mRNA relative expression than those fed with the other diets（ P 〈 0. 05）.However,survival and plasma total cholesterol content were unaffected by dietary CHO∶ L ratio. The optimal range of CHO∶ L within 2. 01- 2. 16 is suitable for juvenile obscure puffer based on second-order polynomial regression analysis of SGR,PER and FE against dietary CHO∶ L ratio,respectively.