Ethyl caffeate modulates systemic and mucosal immune responses, growth performance, and disease resistance against Vibrio parahaemolyticus in hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂)

Hybrid groupers become one of the important aquatic animals, but gastric pathogen infection causes losses due to Vibrio sp. infections. Ethyl caffeate (EC), a naturally occurring antioxidant and antibacterial derived from medicinal plant. This study investigated the effects of EC on the immune response, growth performance, as well as the systemic and mucosal immunity following Vibrio parahaemolyticus challenge. The hybrid groupers were fed diets containing EC at the concentrations of 0, 0.1, 0.25, and 0.5 g/kg (control, EC0.1, EC0.25, and EC0.5 groups, respectively). This feeding trial was conducted in three-part separate experiments consist of non-specific immune response, growth performance and challenge test experiment. The result demonstrated that the EC0.25 group had the highest total leukocyte count, phagocytic activity, and respiratory burst (O₂⁻) and the highest upregulation of genes related to antioxidant activity, inflammation, antimicrobial peptides, and stress. Furthermore, higher growth performance was observed in all EC groups than in the control group with the EC0.25 group exhibited optimum growth performance. According to the challenge test results, the EC0.25 group exhibited strong resistance to V. parahaemolyticus, with a survival rate of 96.7 %. This study elucidated a novel self-defense mechanism after EC modulating against V. parahaemolyticus challenge in hybrid groupers. The EC0.25 group had increased leukocyte subpopulation and the highest upregulation of Toll-like receptor 4, Toll-like receptor 21, MyD88, major histocompatibility complex II, immunoglobulin M, interleukin-1β, and tumor necrosis factor-α in both systemic and mucosal related-organs. Overall, dietary EC0.25 increased the hybrid groupers health status, activated multiple signaling pathways, and synergistically increased the host's systemic and mucosal immunity.