Effects of Dietary Protein and Lipid Levels on the Growth of Orange-spotted Grouper（Epinephelus coioides）

Key words: 
• Epinephelus coioides /
• feeding regime /
• protein /
• lipid /
• growth

Abstract: Orange-spotted grouper（ Epinephelus coioides） was fed diets containing different levels of protein（ 48%,43%,38%） and lipid（ 12%,10%,8%） at different feeding regimes for 8 weeks. The grouper fed the diets containing different levels of protein or lipid in the afternoon showed no significant difference（ P ＞ 0. 05） in weight gain（ WG）,feed efficiency（ FE） condition factor,hepatosomatic index（ HSI） and viscerosomatic index（ VSI）. The grouper fed the high protein and low lipid（ HP-LL） diet in the afternoon had significantly lower protein ratio [（ 1. 39 ± 0. 23） %] than those fed the low protein and high lipid（ LP-HL） diet（（ 1. 81 ± 0.30） %）,and had significantly lower body lipid content than those fed the other diets; the grouper fed the high protein and medium lipid（ HP-ML） diet showed significantly higher body protein content [（ 170. 9 ± 1. 5） g·kg^-1]and muscle protein content [（ 215. 9 ± 3. 9） g·kg^-1]than those fed the other diets. The grouper fed the HP-LL diet contained evidently lower glutamate pyruvate transaminase（ GPT）,albumin and total protein than those fed the high protein and high lipid（ HP-HL） diet and the HP-ML diet but had significantly（ P ＜ 0. 05）higher liver glucose-6-phosphate dehydrogenase（ G-6-PD） activities than those fed the other diets. The grouper fed the LP-HL diet had significantly（ P ＜ 0. 05） higher liver isocitrate dehydrogenase（ IDH） activities than those fed the other diets. Number of hepatocytes did not significantly differ among the grouper fed the experimental diets. The grouper fed the LP-HL and HP-LL diets exhibited enlarged hepatocytes with apparent steatosis in hepatocyte,and their hepatocytes contained the most vacuoles among those fed the other diets. It is concluded that reducing dietary protein level（ 43% or 38%） or lipid level（ 10% or 8%） in the diet fed in the afternoon did not give any negative impact to the growth of the grouper when the grouper were fed the HP-HL diet in the morning.