eDNA metabarcoding reveals differences in fish diversity and community structure in Danjiang River.

Fish diversity, an important indicator of aquatic ecosystem health, is declining due to water pollution, overfishing, climate change, and invasive species. Effective surveying and monitoring are required to protect fish diversity. Here, a high-sensitivity environmental DNA (eDNA) metabarcoding technique was used to investigate fish diversity in the Danjiang River, Shaanxi Province, China. In total, 59 species were identified in eight orders, 19 families, and 40 genera. Cypriniformes and Perciformes were the main groups in the survey area, while Cyprinidae accounted for 50.85% of the total fish species. Rhinogobius similis (19%), Hemibarbus umbrifer (11%), Gnathopogon herzensteini (10%), Triplophysa stewarti (8%), and Zacco platypus (7%) were the dominant species. Eight rare and two exotic fish species were identified. Combined with analysis of historical data, the richness of fish identified using eDNA metabarcoding was significantly higher than that of fish captured in ground cages. Temperature, pH, and oxidation-reduction potential are the main environmental factors that affect the spatial distribution of fish communities. These results suggest that eDNA metabarcoding could be a new tool with broad application prospects; however, local databases must be improved. This study provides theoretical data and a methodological reference for protecting and managing fish diversity in the Qinling Mountains.