Effects of supplemental phytosterol on growth performance, body composition, serum biochemical indexes and lipid metabolism of juvenile large yellow croaker (Larimichthys crocea) fed with high lipid diet

The aim of the present study was to investigate effects of supplemental phytosterol (PS) on growth performance, body composition, serum biochemical indexes, and lipid metabolism of juvenile large yellow croaker (Lar-imichthys crocea) fed with high lipid diet. The diet with high lipid content (lipid level at 18%) was used as the control diet, and other three diets were formulated with supplementation of 0.5%, 1.0%, and 1.5% PS, respectively, on basis of the control diet. Each diet was randomly fed to triplicate cages for 10 weeks. Results showed that the survival rate, final body weight, specific growth rate, and feed conversion ratio were not significantly different among dietary treatments (P 0.05). Oil red O staining analysis showed that the diet with PS significantly reduced the number and volume of lipid droplets in liver compared with the control diet (P < 0.05). The liver and serum lipid levels were also significantly lower in diets with 0.5% and 1.0% PS than those in the control diet (P < 0.05). Fish fed diets with 0.5% and 1.0% PS showed significantly higher activities of catalase and superoxide dismutase, and lower malondialdehyde content in the liver than those in the control diet (P < 0.05). In the intestine, genes expression of lipid absorption (srbi and npc1l1) and esterification (acat, mtp, and apob100) in fish fed with 0.5% PS were significantly lower than those in the control diet whereas genes expression of cholesterol reverses transport (abca1, abcg5, and abcg8) in diets with PS were significantly higher than those in the control diet (P < 0.05). In the liver, compared with the control diet, supplemented with 0.5% PS significantly downregulated genes expression of lipid synthesis (srebp1, acc, fas, scd1, dgat2, srebp2, hmgcr, and dhcr7) whereas genes expression of lipid catabolism (ppar alpha, aco, cpt1, atgl, and cyp7a1) and cholesterol reverse transport (abcg5 and abcg8) were significantly upregulated (P < 0.05). Thus, dietary PS could reduce adverse effects of high lipid diet on juvenile large yellow croaker by the beneficial regulation of lipid metabolism-related genes in the intestine and liver, and the optimal supplement level of PS in high lipid diet was approximately 0.5% in this study.