Structural characteristics of gut microbiota in Pseudogastromyzon fasciatus and their ecological implications.

Understanding the gut microbiota composition of endemic fish species is crucial for evaluating their ecological adaptations. In this study, we investigated the gut microbiota structure of Pseudogastromyzon fasciatus, an endemic fish species in southeastern coastal China, using 16 S rRNA high-throughput sequencing across seven locations in the Wuyi Mountains-Xianxialing region. A total of 525,058 valid sequences were analyzed, resulting in 3,432 operational taxonomic units (OTUs). To better characterize the host-associated gut microbiota, cyanobacterial sequences-likely derived from dietary sources rather than resident taxa-were excluded from the main community analysis and examined separately due to their potential ecological relevance to feeding. After removing cyanobacterial sequences, the dominant bacterial phyla were Proteobacteria (52.73%), Firmicutes (18.56%), and Bacteroidetes (12.73%). Within the gut cyanobacterial community, 34 genera and 44 species were identified, with the most abundant being an unclassified genus within the family Leptolyngbyaceae (58.62%).Significant differences in alpha diversity were observed across sites, with agricultural areas exhibiting higher diversity (Shannon index: 5.26) compared to urbanized regions (Shannon index: 2.03). Samples from areas with high human activity showed reduced microbial diversity and an increased abundance of potentially harmful bacteria (e.g., Tychonema). These findings provide insights into host-microbe interactions in P. fasciatus and suggest that gut microbiota composition could serve as a sensitive bioindicator for monitoring aquatic ecosystem health.