Effects of dietary vitamin A supplementation on growth, immune response, and lipid metabolism in mid-stage Epinephelus coioides

In a 70-day experiment, we conducted a study to investigate the impact of vitamin A supplementation on growth performance, immunology, and fat metabolites in mid-stage groupers (Epinephelus coioides). The experimental diets were enriched with six different levels of vitamin A: 0 (control group), 1000, 2000, 4000, 8000, and 20,000 IUVAkg-1. Each group in the experiment consisted of three replicates, totaling 540 fish randomly distributed among 30 tanks, with an initial average weight of 81.50 ± 0.05 g. The findings of the study revealed that the group supplemented with 1000 IU/kg of vitamin A exhibited the highest weight growth rate (WGR) and specific growth rate (SGR), as well as the lowest feed conversion ratio (FCR). No mortality was observed in any of the treatment groups. Additionally, the activity of acid phosphatase (ACP) increased with higher levels of vitamin A supplementation, with the control group displaying the lowest value. The 1000 IU/kg treatment showed the highest serum superoxide dismutase (SOD) activity, indicating that adequate vitamin A intake can protect the antioxidant system from oxidative stress. Furthermore, fatty acid synthase (FAS) mRNA activity was up-regulated in fish fed with increasing dietary vitamin A. The broken-line regression model can accurately represent the correlation between WGR and the optimal vitamin A dosage in E. coioides during the mid-stage. This model indicates that the ideal vitamin A dose for optimal results is 1493 IU/kg. This dosage has enhanced growth performance, boosted immune response, and improved lipid metabolism in E. coioides.