Environmental DNA for Assessing Population and Spatial Distribution of Spinibarbus caldwelli in the Liuxi River

The wild resources of Spinibarbus caldwelli, once an important economic fish in southern China, have been drastically reduced in recent years due to environmental changes and human activities. The Liuxi River S. caldwelli National Aquatic Germplasm Reserve was established in Conghua District, Guangzhou city, and the release of S. caldwelli was carried out. However, traditional fishery resource survey methods yield less accurate results when the abundance of the surveyed species is low or when they are difficult to catch. As a non-destructive and non-invasive approach, environmental DNA (eDNA) is widely employed in aquatic species monitoring, though its detection efficiency may be affected by environmental conditions. Therefore, this study explored the eDNA monitoring methods of S. caldwelli in Liuxi River from the following four aspects: (1) the relationship between eDNA release and biomass/abundance; (2) the concentration and diffusion range of eDNA over time in a lentic ecosystem; (3) the diffusion range of eDNA in a lotic ecosystem; and (4) the effects of eDNA application in field monitoring. Our results showed a correlation between eDNA concentration and abundance/biomass of S. caldwelli. eDNA of S. caldwelli can diffuse up to 18 m in lentic ecosystems within 2 h and decreases with distance. eDNA of S. caldwelli released by 10 individuals in Liuxi River could be detected 900 m downstream. Field studies in Liuxi River showed that the eDNA method has high sensitivity in detecting the presence or absence of species and is highly consistent with the results of traditional methods. This study explored the application of environmental DNA technology in species monitoring in Liuxi River. Our aim was to evaluate the applicability and potential of eDNA in ecological monitoring of stream fishes.