Environmental DNA metabarcoding revealing fish species diversity in the Zhelin Reservoir

Abstract

Reliable fish biodiversity baselines are essential for monitoring and adaptive management in large subtropical reservoirs. Environmental DNA (eDNA) metabarcoding provides a non-invasive approach for assessing fish assemblages, but molecular baseline information remains limited for Zhelin Reservoir in the Poyang Lake Basin. In this study, eDNA metabarcoding targeting the mitochondrial 12S rRNA gene was used to characterize fish community composition, diversity patterns and exploratory environment-community associations across 14 sampling sites in December 2023. A total of 85 fish taxa were detected, belonging to 6 orders, 12 families and 59 genera, with Cypriniformes and Cyprinidae being dominant. The taxa with the highest relative read abundances were Xenocypris microlepis , Aristichthys nobilis , Carassius auratus , Cyprinus carpio and Ctenopharyngodon idella , indicating high relative detection intensity of several widespread cyprinids. After rarefaction to an equal depth of 388,125 reads, expected richness was higher upstream, whereas Shannon diversity, Simpson diversity and Pielou evenness did not differ significantly among reservoir sections. Bray-Curtis beta-diversity analysis showed no significant compositional separation among upstream, middle and downstream sections (PERMANOVA: R 2 = 0.223, p = 0.160), and PERMDISP indicated similar multivariate dispersion (p = 0.379). RDA after variance inflation factor screening suggested a significant but exploratory association between measured environmental variables and fish community composition ( R 2 = 0.600, p = 0.045), with dissolved oxygen showing the strongest single-variable association. Overall, this study provides a molecular inventory and monitoring baseline for fish communities in Zhelin Reservoir, supporting future repeated surveys and adaptive reservoir management.