Spatiotemporal patterns of fish diversity in a dammed river: eDNA evidence from the Jialing River and conservation implications

Cascade hydropower development represents a significant anthropogenic pressure on freshwater ecosystems, potentially reshaping fish diversity and community structure. Using environmental DNA (eDNA) metabarcoding within a spatial comparative design—in the absence of pre-dam baseline data—this study investigated fish diversity patterns in the mainstem of the Jialing River, the largest tributary in the Upper Yangtze Basin, China. A total of 113 fish species were identified across 20 reservoir segments. The communities were predominantly composed of lentic-adapted species characterized by benthic habits, omnivorous diets, adhesive eggs, early maturity, small size, and non-migratory behavior—in comparison to historical records. While no significant differences in α-diversity were detected among river sections, β-diversity analysis revealed higher community similarity in the intensively dammed middle reach (14 dams/389 km; Jaccard = 0.7688, β sorenson = 0.2105) compared to the upper (4 dams/560 km; Jaccard = 0.7431, β sorenson = 0.2414) and lower reaches (1 dam/137 km; Jaccard = 0.7179, β sorenson = 0.2691), suggesting a potential homogenization trend associated with dam density. Redundancy analysis (RDA) identified altitude (R 2 =63.31%, P < 0.01) and reservoir length (R 2 =36.71%, P < 0.01) as key factors shaping community differentiation. Seasonal variabilities significantly influenced community turnover, with chemical oxygen demand (COD) during flood season playing a major role in temporal dynamics. This study provides a baseline assessment of fish diversity patterns in a heavily dammed river system, offering insights for conservation planning.