Effect of the active form of vitamin D₃ on growth performance and immune-related gene expression in giant grouper (Epinephelus lanceolatus)

This study investigated the effects of dietary supplementation with the herbal active form of vitamin D₃ (AcD; Phytobiotics Futterzusatzstoffe GmbH, Germany) on the growth performance, immune response, and disease resistance of giant grouper (Epinephelus lanceolatus). Fish were fed a commercial diet (control) or the same diet supplemented with 0.01 % AcD (AcD100) or 0.02 % AcD (AcD200) for eight weeks: After 8 weeks of feeding, various growth parameters (final weight, weight gain, and specific growth rate) showed an increasing trend with AcD concentration, with AcD200 treatment significantly improving growth performance and the feed conversion ratio. Both innate (lysozyme activity) and adaptive (immunoglobulin M expression) immune responses were upregulated in AcD-supplemented fish, particularly in the AcD200 treatment. The proinflammatory cytokines interferon-gamma and interleukin-1 beta increased in the AcD200 treatment, whereas the anti-inflammatory cytokine interleukin-10 was upregulated with high AcD supplementation and long feeding durations. Growth-related genes (insulin-like growth factor 1 and growth hormone) were also enhanced in AcD200 treatment. Although no significant differences in resistance to Streptococcus iniae infection were observed among treatments, AcD supplementation mitigated hepatic lipidosis and modulated inflammatory responses under pathogenic stress. In conclusion, dietary supplementation with 200 mg/kg AcD is a promising herbal feed additive for enhancing growth performance, modulating immune responses, and improving the overall health of giant grouper.