饲料锌对团头鲂幼鱼生长性能、血清生化指标和抗氧化功能的影响

Effects of dietary zinc on growth, serum biochemical indices, and antioxidant responses in juvenile blunt snout bream, Megalobrama amblycephala

以酪蛋白和明胶为蛋白源,七水硫酸锌（Zn SO4·7H2O）为Zn源,分别配制成7种Zn含量（7.4 mg/kg、20.3 mg/kg、32.1 mg/kg、51.0 mg/kg、84.4 mg/kg、169.7 mg/kg、332.4 mg/kg）的半纯化饲料,投喂初始体重为（3.6±0.1）g团头鲂（Megalobrama amblycephala）12周,考察Zn对团头鲂幼鱼生长性能、血清生化指标和抗氧化功能的影响,确定团头鲂幼鱼对饲料Zn的需要量。结果表明,随着饲料Zn含量增加,团头鲂增重率、特定生长率和全鱼Zn含量呈先增加后稳定的趋势;全鱼水分含量显著降低（P〈0.05）,粗蛋白含量显著增加。饲料Zn含量对团头鲂饲料系数无显著影响。饲料中添加Zn显著影响血清总蛋白、尿素氮、高密度脂蛋白胆固醇、总胆固醇以及甘油三酯含量,而对血清白蛋白含量和碱性磷酸酶活性无显著影响。随着饲料中Zn含量的增加,团头鲂肝丙二醛含量显著降低（P〈0.05）,而肝过氧化氢酶和超氧化物歧化酶活性在各处理间均无显著差异。折线回归分析表明,团头鲂幼鱼（体重3.6~26.7 g）获得最佳生长时对饲料Zn需要量为32.6 mg/kg,获得最大鱼体Zn含量时Zn的需要量为47.6 mg/kg。本研究旨在确定团头鲂幼鱼对饲料中Zn的需要量,为配制团头鲂高效环保饲料提供科学依据。

Zinc（Zn） is an essential trace element in fish. It functions as a cofactor in several enzyme systems and is involved in many important physiological processes, including improved growth and development, immune function, and defense against free radicals. Signs of impaired growth, increased mortality, cataracts, short body dwarfism, and low tissue Zn may occur in fish fed a Zn-deficient diet. In contrast, excessive dietary Zn can negatively affect the nutritional status of other elements, such as iron, cadmium, and magnesium. Therefore, it is necessary to ensure minimal dietary levels to meet the requirement and be certain that levels do not exceed the maximal limits, which can affect growth and other responses in fish. Blunt snout bream（Megalobrama amblycephala） is in the Cyprinidae family, which is one of the largest fish families in the world. Production of cyprinids reached about 0.71 million tons in 2011, which is the seventh most freshwater-cultured fish species in China（Bureau of Fisheries of the Ministry of Agriculture, China, 2012）. The blunt snout bream has become an important and popular freshwater species. The dietary zinc requirement forblunt snout bream is reportedly 20–184 mg/kg. We conducted a 12-week growth experiment to quantify the optimum dietary Zn requirement of juvenile blunt snout bream and evaluated its effects on antioxidant responses in this species. Seven experimental diets were formulated to contain graded levels of Zn（7.4 mg/kg, 20.3 mg/kg, 32.1 mg/kg, 51.0 mg/kg, 84.4 mg/kg, 169.7 mg/kg, and 332.4 mg/kg diet, supplied as Zn SO4·7H2O. Casein and gelatin were used as dietary protein sources）. Each diet was assigned to three replicate groups of 40 fish [initial body weight,（3.6±0.1） g] cultured in 500-L aquaria（r=0.9 m, h=0.75 m）. The results showed that the rate of weight gain increased linearly with the increase in dietary Zn level, then remained nearly unchanged in the high Zn treatment groups（≥32.1 mg/kg）. Specific growth rate and fish Zn content showed a similar tendency with rate of weight gain. Whole body moisture content of blunt snout bream decreased significantly in the supplemented groups compared to that in the un-supplemented group（P〈0.05）, whereas whole body crude protein content increased significantly in the supplemented groups compared to that in the un-supplemented group（P〈0.05）. No significant difference was observed in the food conversion rate among the treatments（P〉0.05）. The serum chemistry analysis showed that dietary Zn had significant effects on contents of total protein, urea nitrogen, high density lipoprotein cholesterol, total cholesterol, and triglycerides（P〈0.05）, but no effect on albumin content or alkaline phosphatase activity（P〈0.05）. Hepatic malondialdehyde content decreased significantly（P〈0.05）, whereas superoxide dismutase and catalase remained unchanged with increases in the dietary Zn supplement rate（P〉0.05）. A broken-line regression analysis showed that the optimum dietary Zn requirement of blunt snout bream was 32.6 mg/kg for maximum growth and 47.6 mg/kg for maximum fish Zn concentration. These results increase our knowledge of the zinc requirement in blunt snout bream to enhance the feed quality and discover the versatile functions of Zn in blunt snout bream.