Protective Effects of Carvacrol Against Vibrio harveyi Infection in Sebastes schlegelii and Its Underlying Mechanisms

The inappropriate use of antibiotics in aquaculture has exacerbated antimicrobial resistance in pathogens, thereby reducing the efficiency of aquaculture production. Therefore, it is crucial to develop effective antibiotic alternatives capable of inhibiting pathogenic bacteria. Against this background, the present study investigated the efficacy and underlying mechanism of carvacrol against Vibrio harveyi in the mariculture of the marine fish Sebastes schlegelii, aiming to provide data support for the development of green fishery drugs to replace antibiotics. The results indicated that pre-treatment with carvacrol increased the survival rate of infected S. schlegelii. Meanwhile, post-infection administration of carvacrol alleviated intestinal pathological damage. Carvacrol regulated host immunity by modulating the transcription of the immune-related genes NF-κB/RelA and IL-15. Carvacrol did not significantly alter the activities of SOD, MDA, or CAT, suggesting that the oxidative defense pathway was not primarily involved. Analysis of intestinal Vibrio 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 and peripheral blood. 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.