饲料蛋白和脂肪水平对云纹石斑鱼幼鱼免疫和抗氧化性能的影响

Effects of dietary protein and lipid levels on immune and antioxidant function of juvenile Epinehelus moara

采用蛋白和脂肪水平双因素实验，通过检测云纹石斑鱼血清、肝脏和肌肉中免疫与抗氧化指标，为饲料蛋白和脂肪的适宜配比提供依据。以鱼粉和豆粕作蛋白源，鱼油和大豆油混合油作脂肪源，3个蛋白水平分别为：35％、40％、45％，每个蛋白水平分别设3个脂肪水平：9％、12％、15％，每组3个重复。LZM活力和IgM含量在蛋白水平40％～45％时较高，也呈现随脂肪水平增加而上升的趋势，且蛋白水平比脂肪水平和交互作用对LZM和IgM有更显著的影响。肝脏SOD活力在40％蛋白水平时较高，在低蛋白水平（35％）时SOD活力随脂肪水平上升而增强，而高蛋白水平（45％）时则相反。蛋白、脂肪水平和交互作用对CAT活力均有显著影响，蛋白水平较高CAT活力较强。肌肉SOD和CAT活力变化趋势与肝脏大致相反。MDA含量随蛋白水平增加而减小，蛋白水平对肝脏和肌肉MDA都有显著作用，随着饲料脂肪水平增加肝脏MDA显著下降。实验表明，饲料中蛋白质含量维持在一定水平（40％左右）是必要的，当蛋白需求满足时，适当增加脂肪水平有利于鱼体健康。

As nutritional components, protein and lipid are essential for maintaining normal physiological activities of fish. Appropriate contents of fish dietary protein and lipid would be beneficial to health and growth, improve protein utilization and meat quality, reduce protein consumption and feed costs. E. moara which has promising developing prospect of aquaculture is the economic species in the southeast coast of China. For the research of appropriate dietary protein and lipid proportion, two factors experiments, protein and lipid, were done, and immune and antioxidant indexes of serum, liver and muscle from E. moara were tested. Experimental dietary protein sources were, fish and soybean meal, lipid sources were fish and soybean mixed oil. Nine experimental dietary groups （3 × 3 ） were designed in this research： three protein groups 35%, 40%, 45%, and three lipid levels in each protein group 9% , 12% , 15%. 540 fishes were randomly selected and transferred into 27 circular cages （depth 0.8m, diameter 1.2m）, and cages were placed in rectangular cement tanks （ length 7.5 m, width 2.5 m, water depth 1 m） in order. The maximum of lysozyme （LZM） activity was 9#（45/15 ） ： 66.15 ± 8.77 U mL- 1, the minimum was 1 # （35/9） ： 43.08 ± 13.97 U mL-1. The maximum of immunoglobulin M （IgM） concentration was 9#（45/15）： 1.51 ±0.26 mg mL-1, the minimum was 1#（35/9）： 0.65 ±0.26 mg mL-1. LZM activity and IgM concentration kept a high level, increased with the increase of lipid levels when protein levels were 40 - 45%. The effect of protein level was more significant than lipid level and interaction on LZM activity and IgM concentration. The variation range of liver super oxide dismutase （SOD） activity was 82.65±16.75 - 112.59 ± 17.34 U mgprot-1, the range of muscle SOD was 10.34 ±0.72 - 12.89 ± 1.43 U mgprot-1. Liver SOD activity was high in 40% protein level, and it enhanced with the increase of lipid levels when protein levels were low： 35%. The situation in high protein level （45%） was on the contrary. The variation range of liver catalase （CAT） activity was 5.38 ± 1.37 - 11.51 ±1.62 U mgprot-1, the range of muscle CAT was 0.11 ±0.05 - 0.41± 0. 11 U mgprot-1. The effects of protein, lipid level and interaction on CAT activity were all significant, and the higher protein level was, the more actively CAT was. In this experiment, the variation trend of SOD and CAT activities in liver was roughly opposite to them in muscle. The variation range of malondialdehyde （MDA） in liver was 5.56 ±0.78 - 10.50 ± 1.90 nmol mgprot -1, in muscle was 1.34 ± 0.26 -2.93±0.81 nmol mgprot-1. Liver and muscle MDA content decreased with the increase of protein levels, protein level had a marked impact both on liver and muscle MDA content. But with the increase of lipid levels, content didn＇ t change obviously; lipid level had a marked impact only on liver MDA content. The maximum of total antioxidant capacity （T-AOC） in liver was 7#（45/9）： 2.37± 0. 476 U mgprot-1, the minimum was 4#（40/9） ： 1.13± 0.22 U mgprot-1, the maximum of muscle T-AOC was 6#（40/15 ） ： 0.69 ± 0.17 U mgprot -1, the minimum was 8 # （45/12） ： 0.15 ± 0.06 U mgprot - 1 . T-AOC was high in group 5#（40/12）, 6#（40/15） and 7#（45/9） of which protein levels were in the middle. This experiment suggested that the increasing dietary protein and lipid level could enhance the immunity of Epinehelus moara. And liver is the main reaction site of antioxidant enzymes. When antioxidant enzymes activity of liver was insufficient, oxidative stress would spread to whole body, then antioxidant enzymes activity of muscle would be enhanced to resist damage of oxidative stress. But long-term oxidative stress would cause dropped muscle quality. The growth of fish from 6#（40/15 ）, 7# （45/9）, 8#（45/12）, 9# （45/15） was more quickly than others, and the growth of 4#（40/9）, 5#（40/12）, 6#（40/15 ） showed a significantly increased gradient. It suggested that dietary protein level around 40% was necessary, though lipid provided energy more efficient than protein, until requirement for protein of body had been adequate, increase of lipid level would promote health of fish. But the effects of protein on the health of fish was not obvious when protein level was too high.