Impact of dietary gallic acid on growth indices and the expression of antioxidant, stress, and immunity-related genes in rainbow trout (Oncorhynchus mykiss)

his study investigates the effects of dietary gallic acid (GA) supplementation on growth performance and the expression of genes linked to antioxidant, stress, and immune functions in rainbow trout (Oncorhynchus mykiss). Fish with an average body weight of 2.84 ± 0.25 g were fed diets containing 0 mg/kg (control), 300 mg/kg (G300), 450 mg/kg (G450), and 600 mg/kg (G600) of GA over 60 days. The results revealed significant improvements in growth indices, including weight gain, specific growth rate, and feed conversion ratio, in GA-supplemented groups compared to the control (P<0.05). At the molecular level, GA supplementation significantly upregulated the expression of antioxidant-related genes (SOD, CAT, GPX), stress-related genes (HSP70), and immune-related genes (TNF-α, IL-1β). The G300 group consistently exhibited the most pronounced transcriptional responses, while higher doses (G450 and G600) showed diminished or inconsistent effects. These findings suggest that a dietary inclusion of 300 mg/kg GA optimally enhances fish health and productivity by modulating key molecular pathways. This dosage is recommended as an effective feed additive for improving the performance and resilience of rainbow trout in aquaculture.