吉富罗非鱼对饲料亚油酸的需要量

Optimal dietary linoleic acid requirement for the advanced juvenile GIFT strain of Nile tilapia,Oreochromis niloticus

选用初始体重为（60．98±3．82）g的吉富罗非鱼（Oreochromis niloticus）630尾，随机分成7组（每组设3个重复，每个重复30尾），饲喂亚油酸含量分别为0．07％（对照组）、0．36％、0．61％、1．03％、2．00％、3．00％和4．15％的7种半纯化等能等氮饲料10周。结果表明，鱼体增重率、饲料效率、蛋白质效率和蛋白质沉积率均在亚油酸水平为1．03％时较对照组差异显著（P〈0．05），且均在饲料亚油酸水平为2．00％时达到最大。经二次回归分析，饲料亚油酸水平为2．49％和2．66％时吉富罗非鱼分别获得最大增重率和最高饲料效率。通过折线回归发现饲料亚油酸水平为1．02％时，吉富罗非鱼获得最大蛋白沉积。肝体比和脏体比均随亚油酸水平的升高而升高，当饲料亚油酸含量为0．61％～4．15％时显著高于对照组（P〈0．05）。亚油酸添加组的肌肉粗脂肪含量显著高于对照组（P〈0．05）；当饲料亚油酸含量为1．03％-4．15％时，肝和全鱼粗脂肪含量显著高于对照组（P〈0．05）。随饲料亚油酸水平升高，血清甘油三酯和总胆固醇变化趋势一致，呈现先下降后上升的趋势，经二次回归分析亚油酸水平为1．63％时血清甘油三酯含量最低；各亚油酸添加组的血清高密度脂蛋白胆固醇含量显著高于对照组，且在饲料亚油酸含量为1．13％时达到最大（P〈0．05）；当饲料亚油酸水平为1．03％-4．15％时，血清低密度脂蛋白胆固醇含量显著低于对照组（P〈0．05）。随饲料中饱和脂肪酸（ESFA）含量下降，吉富罗非鱼肌肉和肝脏ZSFA含量均呈下降的趋势；随饲料亚油酸水平增加，肌肉和肝脏的n-6多不饱和脂肪酸（Zn-6PUFA）含量呈上升趋势，肌肉和肝脏的∑n-3PUFA含量呈下降趋势。综上所述，初始体重为（60．98±3．82）g的吉富罗非鱼饲料亚油酸需要量为1．02％～2．66％。

The Genetically Improved Farmed Tilapia （GIFT, Oreochromis niloticus） strain is one of the more suc- cessfully introduced farmed tilapia in China because of its strong adaptability, rapid growth, high fecundity, and ability to accept a broad diet. Similar to other fish and vertebrates, tilapia cannot synthesize 18-carbon polyun- saturated fatty acids （PUFAs） and, thus, require a dietary source of n-6 series FAs （18：2n-6 or 20： 4n-6） for nor- mal growth and reproduction. Although the optimum n-6 FA dietary requirements for tilapia 〈 10 g have been es- timated to be 0.5%-1.0%, few studies have investigated the linoleic acid （LA） requirement for larger juvenile tila- pia. Our objective was to determine the optimal dietary LA requirement for larger juvenile GIFT. A total of 630 fish （mean body weight, 60.98±3.82 g） were divided randomly into seven groups with three replicates of 30 fish in each replicate. Seven diets with a constant dietary lipid level （8%） were formulated to contain seven levels [0.07% （control group）, 0.36%, 0.61%, 1.03%, 2.00%, 3.00%, and 4.15%] of LA by supplementation with corn oil and palmitic acid to modulate FA contents. The fish were fed three times daily （8：30, 12：30, and 16：30） to apparent satiation for 10 weeks. At the end of the feeding trial, growth performance, body composition, serum biochemical indices, and FA composition were measured. The results showed that weight gain rate （WGR）, feed efficiency rate （FER）, protein efficiency rate, and protein retention rate （PRR） of GIFT increased initially and then decreased as LA level increased. A second-order regression analysis showed that the optimal LA level for the best WGR was 2.49%, and that the dietary LA level for the best FER was 2.66%. Broken-line regression analyses of PRR against dietary LA level indicated that the dietary LA level for the best PRR was 1.02%. Increasing dietary LA level con- tributed to increase tissue and whole-body lipid levels. Serum total cholesterol and triglyceride （TG） levels were lowest in the group fed 1.03% LA, whereas the 1.03% LA group had the highest high-density lipoprotein choles- terol level. Low-density lipoprotein cholesterol content declined as LA increased. Broken-line regression analyses showed that the optimum LA requirement for the minimum TG level was 1.13%. Tissues FA composition was af- fected by dietary FA composition. Muscle and liver saturated fatty acid levels declined as dietary level decreased; however, muscle and liver n-6 FA levels increased and n-3 FA levels declined with the increase in LA level. Our comprehensive analysis of growth performance, serum biochemical indices, and FA composition in muscle and liver suggests that the optimal level of dietary LA for later-stage juvenile GIFT is 1.02%-2.66%.