Metagenomic insights into sex-specific taxonomic and functional differentiation of epidermal mucus microbiota in the humphead wrasse (Cheilinus undulatus).

The humphead wrasse (Cheilinus undulatus) is a large coral reef fish of high ecological and economic importance, whose epidermal mucus microbiota plays a critical role in host defense, immune regulation, and environmental adaptation. However, the influence of host sex on the structure and functional potential of epidermal mucus microbiota remains poorly understood. In this study, epidermal mucus samples were collected from sexually mature female and male humphead wrasse, and shotgun metagenomic sequencing was performed to systematically compare microbial community composition, diversity, and functional gene profiles between sexes. The results showed no significant differences in alpha diversity (ACE and Shannon indices) between female (FM) and male (M) groups. In contrast, beta diversity analyses and hierarchical clustering revealed clear sex-related separation of microbial community structures at both phylum and genus levels. Although both groups were dominated by Pseudomonadota, Bacillota, Bacteroidota, and Verrucomicrobiota, their relative abundances and sex-specific taxa differed markedly. Functional annotation based on KEGG indicated that female-specific taxa harbored a greater number and broader range of functional genes, mainly associated with carbohydrate, amino acid, energy, and cofactor metabolism, as well as disease-related pathways. Furthermore, Comprehensive Antibiotic Resistance Database (CARD) and the Virulence Factor Database (VFDB) analyses revealed that female-specific taxa exhibited higher diversity of antibiotic resistance genes and virulence factors, whereas male-specific taxa showed a more limited functional repertoire, primarily related to basic metabolism and biofilm formation. Overall, this study demonstrates pronounced sex-associated differences in both the taxonomic composition and functional potential of epidermal mucus microbiota in humphead wrasse, highlighting the importance of host sex in shaping host-microbiome interactions and providing new insights for health management and conservation of coral reef fishes.