Antibiofilm from phyllosphere improves survival and gut health of juvenile pearl gentian hybrid grouper challenged with Vibrio harveyi

The widespread use of antibiotics in aquaculture has become increasingly ineffective due to the emergence of antibiotic-resistant bacteria, residual contamination, the disruption of aquatic microbiota, and international trade restrictions on antibiotic-laden products. As a sustainable alternative, this study investigated the effects of antibiofilm compounds derived from phyllosphere bacteria on the culture performance of juvenile pearl gentian hybrid grouper (Epinephelus fuscoguttatus × E. lanceolatus) challenged with Vibrio harveyi. Juveniles (1.973 ± 0.177 g; 3.421 ± 0.177 cm) were acclimated and distributed into 12 fiber tanks (300 L) at a density of 200 fish per tank. Fish were fed commercial feed supplemented with antibiofilm at concentrations of 0.01, 0.05, and 0.1 mL/kg for four weeks, alongside an unsupplemented control group. Culture was maintained under a flow-through system (10 mL/s). Evaluated parameters included growth, survival, deformity rate, skin pigmentation, water quality, total bacterial and Vibrio abundance, and intestinal morphology, which was assessed via scanning electron microscopy (SEM) and histological analysis (goblet cell count, mucosal fold height, and muscularis thickness). A challenge test was conducted by intraperitoneal injection of V. harveyi (2.3 × 10⁸ CFU/mL; 0.1 mL/fish), followed by a seven-day observation period. The results indicate that while growth was not significantly affected (P > 0.05), fish receiving 0.01 mL/kg antibiofilm exhibited significantly higher survival (P < 0.05) during both the feeding trial and the post-challenge period. Compared to the control group, deformity rates were significantly lower (P < 0.05), and skin brightness improved in all antibiofilm treatments. SEM analysis revealed improved intestinal microvilli structure in treated groups, indicative of enhanced gut health. Furthermore, a reduced abundance of Vibrio spp. and increased blood granulocyte levels in antibiofilm-fed fish suggest enhanced immune responses. These findings support the potential of antibiofilm supplementation as a promising, eco-friendly strategy for disease prevention and health management in aquaculture.