Environmental DNA Reveals the Influence of Human Activities on Fish Community Variation Across a Large River and Its Connected Lakes

The aquatic environments of main stems in large rivers and their connected lakes exhibit significant disparities under human activities. Fish are crucial for sustaining the structure and function of aquatic ecosystems as high-level predators. This study investigated fish communities in 192 samples from lakes and rivers across the Yangtze river (YR) basin utilizing environmental DNA (eDNA) technology. Additionally, the environmental variable impact on fish biodiversity in these two aquatic environments was uncovered. Herein, we identified approximately 230 fish taxa in this basin, with lakes and rivers comprising both prevalent and habitat-specific species. Water quality played different roles in affecting fish diversity in these two water systems. The geography traits, including Longitude, Latitude, and Altitude, as well as the water traits conductivity (CD), demonstrated the variance in fish diversity and community composition in both rivers and lakes. The human activity factors, including permanganate index (PMI), chlorophyll-a (CHLA), and SiO 2 , elucidated much more variance in fish diversity and community composition in lakes. These findings suggested that human activity factors exert a more significant influence on fish diversity within lakes compared to rivers. Our outcomes document the complex impacts of water quality on fish diversity in different aquatic habitats of the YR basin and emphasize the distinctive considerations required to protect aquatic biodiversity in this basin. However, it should be noted that eDNA technology provides only a single snapshot of community composition. This method possesses limitations common to all approaches (e.g., detection gaps for certain taxa) as well as inherent biases (such as the difficulty in accurately reflecting the abundance and demographic structure of detected species).