De novo genome hybrid assembly and annotation of the endangered and euryhaline fish Aphanius iberus (Valenciennes, 1846) with identification of genes potentially involved in salinity adaptation

Background
The sequencing of non-model species has increased exponentially in recent years, largely due to the advent of novel sequencing technologies. In this study, we construct the Reference Genome of the Spanish toothcarp (Aphanius iberus (Valenciennes, 1846)), a renowned euryhaline fish species. This species is native to the marshes along the Mediterranean coast of Spain and has been threatened with extinction as a result of habitat modification caused by urbanization, agriculture, and its popularity among aquarium hobbyists since the mid-twentieth century. It is also one of the first Reference Genome for Euro-Asian species within the globally distributed order Cyprinodontiformes. Additionally, this effort aims to enhance our comprehension of the species' evolutionary ecology and history, particularly its remarkable adaptations that enable it to thrive in diverse and constantly changing inland aquatic environments.

2026 tang

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.