Effects of two natural polyphenols (resveratrol and ellagic acid) on growth, immunity, and disease resistance in juvenile Cephalopholis sonnerati

Cephalopholis sonnerati is an emerging high-value marine grouper in China, currently in the early stages of commercial development with limited seed production. This species is characterized by an extended growth cycle and a pronounced susceptibility to opportunistic bacterial pathogens, factors that frequently precipitate the prophylactic and indiscriminate application of antibiotics. This 56-day study evaluated resveratrol (RES) and ellagic acid (EA) (300 mg kg⁻¹) as sustainable alternatives to oxytetracycline (OTC) in juvenile C. sonnerati . Growth, histology, digestive enzymes, antioxidant status, innate immunity, and gut microbiota were assessed. Both RES and EA significantly enhanced systemic growth metrics relative to the control and OTC cohorts, with the RES group exhibiting the optimal morphometric response. Histological analysis revealed that polyphenols reduced liver damage and improved intestinal structure. Both additives increased digestive enzyme activities and bolstered antioxidant capacity, evidenced by higher enzyme levels and lower malondialdehyde concentrations. Innate immunity was strengthened through enhanced respiratory burst and phagocytic activity in head-kidney leukocytes. Microbiome analysis showed that RES enriched beneficial bacteria and optimized metabolic pathways. Following a Vibrio parahaemolyticus challenge, the RES group achieved an 82.5% survival rate—comparable to the OTC group (90%) and significantly higher than the EA (70%) and control (42.5%) groups. These findings demonstrate that RES and EA, particularly RES, are effective immunoenhancing additives that improve health and disease resistance in C. sonnerati , providing a practical and sustainable alternative to antibiotics for this new aquaculture candidate.