Large-scale metagenomic analysis reveals host genetics shapes microbiomes in wild freshwater fish gut and skin

Wild freshwater fish microbiomes remain underexplored despite their ecological and economic importance. Through metagenomic sequencing of 903 gut/skin samples from 121 species in southwest China, we constructed the Wild Freshwater Fish Microbiome Catalog, comprising 705 metagenome-assembled genomes and 3,271 viral operational taxonomic units. Host phylogeny dominates microbial community variation, explaining 48.2% (skin) and 22.28% (gut) of the variation. Significant phylosymbiosis occurs in wild freshwater fish, particularly Cyprinidae, with a stronger skin than gut signal. Deterministic selection underpins phylosymbiosis via host-specific ecological filtering. Lifestyle factors (diet, living water layer) and geographical location also impact microbial communities. Notably, wild freshwater fish microbiota harbor a complete set of vitamin B₁₂de novo biosynthesis genes, with Cetobacterium as a keystone genus with probiotic potential. Our work expands gut and skin microbial genome resources, reveals host-microbe coevolution in freshwater fishes, and provides probiotic resources for aquaculture.