Effects of dietary vitamin A on growth, feed utilization, lipid metabolism enzyme activities, and fatty acid synthase and hepatic lipase mRNA expression levels in the liver of juvenile orange spotted grouper, Epinephelus coioides

A 10-week feeding trial was conducted to investigate the effects of dietary vitamin A (VA) on growth, feed utilization, lipid metabolism enzyme activities, and fatty acid synthase (FAS), and hepatic lipase (HL) mRNA expression levels in the liver of juvenile Epinephelus coioides. Six semi-purified diets were formulated to contain VA as retinyl acetate at concentrations of 0, 1000, 2000, 4000, 8000, and 20,000 IU·kg− 1, providing actual dietary values of 387 (control group), 1256, 2242, 4102, 7635, and 18,231 IU VA·kg− 1 diet, respectively. A total of 540 juvenile E. coioides were randomly stocked into 18,500 L fiberglass tanks with 30 fish per tank and 3 tanks per diet. The results showed weight gain rate (WGR), specific growth rate (SGR), and survival rate (SR), significantly increased in fish supplemented with over 1000 IU dietary VA compared with the control group (P < 0.05). The feed conversion ratio (FCR) significantly decreased in fish supplemented with dietary VA from 2000 IU·kg− 1 to 8000 IU·kg− 1 compared with fish in the other groups (P < 0.05). However, supplementing the diet with VA at > 8000 IU·kg− 1 inhibited the growth of juvenile E. coioides (P < 0.05). The FAS and HL activities were significantly higher in the livers of the group supplemented with 2000 IU VA·kg− 1 compared to those of the control group and the group supplemented with 1000 IU VA·kg− 1 (P < 0.05), but dietary VA did not significantly affect whole body lipid deposition in fish (P > 0.05). The FAS and HL mRNA expression levels were significantly higher in the groups with dietary VA levels from 4000 IU·kg− 1 to 8000 IU·kg− 1 compared to those in the control group (P < 0.05). Based on the broken-line regression analysis of WGR and dietary VA levels, the optimal dietary VA requirement is 1775 IU VA·kg− 1for juvenile grouper. At the same time, under the condition of this experiment, a dietary VA level of 4000 IU·kg− 1 promoted lipolytic enzyme activity and the expression of lipid decomposition genes in the liver of groupers.