Intestinal microbes are closely related to vital host functions such as digestion and nutrient absorption, which play important roles in enhancing host adaptability. As a natural "laboratory", caves provide an outstanding model for understanding the significance of gut microbes and feeding habits in the habitat adaptability of hosts. However, research on the relationship between gut microbes, feeding habits, and the adaptability of troglobites remains insufficient. In this study, we compared the characteristics of the intestinal microbes of Sinocyclocheilus cavefish and surface fish and further established the relationship between intestinal and habitat microbes. Furthermore, we conducted environmental DNA (eDNA) (metabarcoding) analysis of environmental samples to clarify the composition of potential food resources in the habitats of the Sinocyclocheilus cavefish and surface fish. Results showed that the structure of the Sinocyclocheilus gut microbes was more related to ecological type (habitat type) than phylogenetic relationships. While horizontal transfer of habitat microbes was a source of gut microbes, hosts also showed strong selection for inherent microbes as dominant microorganisms. Differences in the composition and structure of gut microbes, especially dominant microbes, may enhance the adaptability of the two Sinocyclocheilus fish types from the perspectives of food intake, nutrient utilization, and harmful substance metabolism, suggesting that food resources, predation patterns, intestinal flora, digestive and absorptive capacity, and feeding habits and preferences are linked to habitat adaptability. These results should facilitate our understanding of the significance of fish gut microbes to habitat adaptation and provide a new perspective for studying the adaptive mechanisms of cavefish.
肠道微生物与宿主的食物消化和营养吸收等多种重要功能密切相关，在增强宿主适应性中扮演了重要的角色。作为一个天然的 "实验室"，洞穴栖息地为了解肠道微生物和摄食习惯在宿主的生境适应性中的意义提供了一个杰出的模型。然而，目前关于肠道微生物、摄食习惯和穴居生物适应性之间关系的研究依然不足。在该研究中，我们比较了金线鲃属洞穴和地表种鱼类肠道微生物的特征，并进一步建立了肠道微生物与它们栖息地微生物之间的关系。此外，我们还对环境样本进行了eDNA（条码）分析，以明确（金线鲃属）洞穴种鱼和地表种鱼类生境中潜在食物资源构成。结果显示，与系统发育关系相比，金线鲃属鱼类肠道微生物的组成和结构与生态类型（生境类型）更相关。然而，生境微生物的水平转移只是鱼类肠道微生物的一种来源，宿主对固有的（肠道）微生物表现出强烈的选择而成为优势微生物。肠道微生物组成和结构的差异，特别是优势微生物的差异，可以从食物摄取、营养物质利用和有害物质代谢等角度增强两类型金线鲃属鱼类的生境适应性。这种联系最终形成了一个通过食物资源-捕食模式-肠道菌群-消化吸收能力以及摄食习惯和偏好的生境适应性环。该研究的结果促进了我们对鱼类肠道微生物对生境适应性意义的理解，为研究洞穴鱼类的适应机制提供了一个新的视角。.
Keywords: Adaptive mechanism; Cavefish; Intestinal microbes; Sinocyclocheilus.