Host habitats influence the gut microbial assembly mechanisms of cold-water fish

Abstract

Due to factors such as overfishing, hydropower development, and water pollution, their wild populations have drastically declined, with many species being classified as endangered or vulnerable. Understanding the driving factors behind the gut microbiota of cold-water fish holds significant implications for conservation. Therefore, to investigate the influence of different factors on the gut microbes of cold-water fish, 112 gut samples from farmed and wild habitats were collected from Schizothorax wangchiachii (herbivorous), Schizothorax kozlovi (omnivorous) and Percocypris pingi (carnivorous), in the Jinping Dahewan range of lower reaches of the Yalong River. The results of 16 S rRNA gene sequencing of the gut contents showed that habitat was the major factor influencing the gut microbes of the three cold-water fishes. In terms of microbial composition, farmed cold-water fish exhibited a dominant bacterial phylum, Proteobacteria (82 %), while those in wild environment presented multiple dominant taxa, such as Proteobacteria (38 %), Fusobacteria (30 %), Firmicutes (11 %), and Cyanobacteria (11 %). Gut microbial diversity, both α diversity and β diversity, in wild cold-water fish was significantly higher than that in farmed individuals. Network complexity of gut microbiota was notably higher in wild cold-water fish than in farmed individuals. From farmed to wild environments, the relative influence of deterministic processes in the gut microbiota assembly mechanism of cold-water fish gradually diminishes, while the contribution of stochastic processes steadily increases. The gut microbiota construction mechanism in farmed cold-water fish was primarily influenced by deterministic processes of homogeneous selection, while in wild cold-water fish, it was mainly driven by stochastic processes of homogeneous dispersal. Overall, this study is an important reference for the study of the gut microbiota of cold-water fish and the conservation of their wild populations.