4 Discussion
The application of nondestructive techniques to monitor and characterize fish diversity has drawn increasing worldwide attention for assessing aquatic ecosystem health. Given that it is difficult and costly to investigate fish diversity in large rivers, finding a new monitoring method with applicable technology has drawn great attention. Negative impacts of increasing anthropogenic activities on aquatic organisms, especially fish, have been verified in the Pearl River and other rivers and reservoirs connected with it (Wang et al., 2020b; Wang et al., 2019a; Wang et al., 2018a; Wang et al., 2019b; Wang et al., 2021a). To protect and maintain the health of subtropical river systems, we investigated the fish diversity along a river continuum using a combination of electrofishing and eDNA metabarcoding. Our results presented evidence that eDNA can be used to monitor fish diversity in this kind of aquatic ecosystem.