Fish diversity in the lower reaches of theHeishui River based on eDNA technology

The Heishui River is an important alternative habitat for fish in the main stream of the Jinsha River's downstream Baihetan reservoir area and a priority protected tributary. In recentIn order to explore a new method for survey of fish diversity in the Heishui River, the fish diversity was detected in samples collected from 11 sampling sections along the lower reaches of the Heishui River from November 2024 and May 2025 by environmental DNA metabarcoding (eDNA) technology. Through the collection of environmental DNA samples and high-throughput sequencing analysis, a total of 57 fish species were detected from the environmental DNA samples in the Heishui River, belonging to 4 orders, 14 families and 40 genera. Among them, the Cypriniformes are the most numerous, with a total of 39 species. The relative abundance of OTU is the highest at 76.45%, followed by the Perciformes at 18.87% and the Siluriformes at 4.68%. The dominant species were the Schistura fasciolata, Cyprinus carpio, Rhinogobius similis, Zacco platypus, Schizothorax kozlovi Nikolsky, Oreochromis niloticus, and Chanodichthys erythropterus. A total of 8 species were detected as unique fish species of the upper reaches of the Yangtze River, including Schizothorax wangchiachii and Schizothorax kozlovi Nikolsky, which were detected in all survey sections. There were 5 alien species, and a large number of Oreochromis niloticus were detected in all survey sections during spring and autumn. The diversity analysis showed that there was no significant difference in the diversity index between autumn and spring, and H11 had the largest number of species, with a fish composition different from other sampling sections. The research results provide detailed data on the fish diversity of the lower reaches of the Heishui River, confirming the feasibility of using eDNA technology to investigate the fishery resources in the river basin, and indicate that when integrated with traditional survey methods, environmental DNA technology can function as a crucial supplementary means for swiftly comprehending the spatiotemporal variations of fish resources within a watershed.