Comparative Study of Fish Diversity in Wanquan River Based on Environmental Technology and Traditional Fishing Gear Survey Methods

Fish play an important role in maintaining aquatic ecosystems and directly affect the health and stability of aquatic ecosystems. The rapid economic development of the Wanquan River basin has seriously affected the ecological function of fish in the basin owing to human activities such as dam dredging and highways. Therefore, long-term surveys and monitoring of fish diversity are urgently required to determine the current status of fish resources in the basin and formulate corresponding conservation measures. Traditional fish surveys primarily use gear fishing methods, such as gillnets, purse seines, and ground cage nets. However, traditional fishing gear survey methods have limitations, particularly because different gears are selective for fish species and individual sizes. Catching fish species that are small in number and elusive is challenging, making it difficult to accurately and comprehensively monitor the fish diversity in the survey area. In addition, the restriction of the fishing moratorium further increases the difficulty of traditional operational surveys. Therefore, a rapid and effective monitoring method is urgently needed to study the fish resources of the Wanquan River. Environmental DNA (eDNA) technology involves analyzing biological communities by enriching DNA retained in the environment and using high-throughput sequencing technology. This method offers several advantages, including minimal environmental disturbance, time and effort efficiency, and allowing rapid monitoring of fish diversity and spatial distribution. eDNA technology has been widely used in biodiversity monitoring, population distribution, biomass assessment, and feeding analysis. To investigate the fish diversity and community structure in the Wanquan River Basin, this study used eDNA technology in combination with the traditional fishing gear survey method for comparative analysis and explored the advantages of the two methods in fish monitoring. The results showed that 76 species of fish in six orders, 32 families, and 65 genera were detected by eDNA technology, whereas 44 species in four orders, 14 families, and 44 genera were detected by the traditional fishing gear survey method. Overall, the eDNA method detected more fish species than the traditional survey method at all sampling sites. The dominant fish species detected by both methods were Carpiformes, followed by Perchiformes and Siluriformes. In terms of the composition of dominant species, 22 dominant species of fishes in Wanquan River were detected by eDNA technology, seven dominant species were detected by the traditional survey method and two dominant species were detected by the two methods, which were Coptodon zillii and Toxabramis houdemeri. Alpha-diversity analyses indicated that the fish species richness detected by the eDNA method was significantly higher than that of the traditional method, whereas the evenness was higher than that of the traditional method. The principal coordinate analysis (PCoA) results revealed that the fish composition at the HP sampling site was less similar to that of the DLQ, JJ, PL, and DBQ sampling sites, with fewer common species. Spearman's correlation analysis showed that eDNA technology and traditional survey methods had a significant positive correlation (P < 0.05) between species sequence abundance and fish quality. This preliminary exploration of the fish diversity of Wanquan River using both the eDNA and traditional survey methods establishes a particular foundation for the application of eDNA in monitoring the fish diversity of Wanquan River and also serves as a reference for the protection of the fish management of Wanquan River.