Protective Effects of Carvacrol Against <em>Vibrio harveyi </em>Infection in <em>Sebastes schlegelii </em>and Its Underlying Mechanisms

Results indicated that pre-treatment with carvacrol significantly increased the survival rate of infected Sebastes schlegelii. Conversely, post-infection administration alleviated intestinal pathological damage. Carvacrol regulated host immunity by modulating the transcription of immune-related genes NF-κB/RelA and IL-15. It had no significant effects on SOD, MDA and CAT, suggesting that the oxidative defense pathway was not involved. Analysis of intestinal Vibrio pathogen load confirmed that carvacrol could inhibit the growth and colonization of intestinal Vibrio, thereby maintaining microbial homeostasis. Immunohistochemistry and peripheral blood flow cytometry showed that carvacrol enhanced the adaptive immunity of fish by increasing the proportions of CD4‑1⁺ T cells and CD79a/CD79b⁺ B cells in tissues. In conclusion, carvacrol enhances the resistance of S. schlegelii against V. harveyi by inhibiting pathogenic bacteria, improving intestinal morphological structure, reducing pathogenic bacterial load to maintain microbial homeostasis, and enhancing the adaptive immunity of the organism. This study provides a theoretical basis and data support for the substitution of antibiotics and the development of green feed additives in aquaculture.