Dietary Effects of a Fermented Botanical Product on Growth, Nutrient Utilization, Oxidative and Immune Responses of Juvenile Greater Amberjack Seriola dumerili

Functional feed additives prepared from various plant products can potentially support fish growth and health in aquaculture. Here, using two feeding trials, we examined the effects of a fermented botanical product (FBP) dietary supplement for greater amberjack juveniles. Trial 1 examined the effects on growth, digestibility, nutrient utilization, and oxidative stress of dietary supplementation with FBP at 0%, 0.1%, 0.5%, 2.0%, or 5.0% (w/w) and fed to fish (initial mean body weight [BW] = 53 g) for 30 days. In Trial 2, the diet was supplemented with FBP at 0, 0.1, 0.5, or 5.0% (w/w) and fed to fish (initial mean BW = 43 g) for 45 days; the fish were then injected intraperitoneally with lipopolysaccharide (LPS) as an immune enhancer to observe nonspecific immune responses; the experiment was conducted at 2‐factorial design (FBP levels × LPS injection) to evaluate the interactive effect between these factors using three replicated tanks. Trial 1 revealed that dietary supplementation with FBP at >0.5% improved growth and feed utilization; the BW gain (BWG) increased by 30%, and protein and lipid retention increased by 10% compared to those of the control group. This was supported by the enhanced intestinal protease activity and reduced plasma oxidative stress. In Trial 2, the gene expression of tumor necrosis factor‐ α ( tnf-α ) and interleukin‐1 β ( il-1β ), immune‐related cytokines expressed in the head kidney, was significantly higher at >0.5% or 5% FBP supplementation than in the control diet group. Based on two‐factor ANOVA, FBP supplementation and LPS injection interactively affected tnf-α gene expression. The amount of skin mucus and its lysozyme activity increased with increasing FBP supplementation. These findings reveal that dietary supplementation at >0.5% FBP may improve growth, nutrient utilization, and health status in juvenile greater amberjack at appropriate supplementation levels.