Host-Associated and Environmental Microbiota of Hatchery-Reared Sichuan Taimen (Hucho bleekeri): Community Structure and Functional Profiling.

The diversity and complexity of symbiotic microbiota in fish may significantly influence the host's physiological, metabolic and immunological functions. In order to understand the microbial assembly in Sichuan taimen (Hucho bleekeri), an endangered fish species in the upper reaches of the Yangtze River, the microbiota of the skin, oral cavity and feces of artificially reared individuals and the microbiota of the rearing water were characterized through metagenomic sequencing. The results demonstrated that Pseudomonadota were shared across the skin, oral cavity, feces and rearing water, suggesting that they may constitute a shared microbial group connecting the aquatic environment and host mucosal surfaces. Based on functional prediction analyses, these taxa were potentially associated with organic matter degradation, nutrient cycling, and microbial and immune homeostasis. Likewise, Actinomycetota and Bacillota were consistently detected across multiple mucosal tissues and were predicted to be associated with nutrient transformation, antimicrobial defense, and the maintenance of mucosal microbial stability. Fusobacteriota were detected solely in feces, suggesting a strong tissue-specific colonization capacity. The alpha diversity of the microbiota did not differ significantly among tissues, and the beta diversity revealed strong clustering of host-associated samples and clear separation from water samples. Functional annotation further revealed that the water microbiota exhibited broader yet more dispersed functional potential, whereas host-associated microbiota showed stronger functional specialization closely aligned with host physiological demands. Collectively, the findings are better presented as baseline information for future comparative and hypothesis-driven studies in Sichuan taimen.