4.4 Use of fish diversity to evaluate the water quality
Considering different monitoring targets, the use of eDNA-based fish monitoring could be summarized into three goals: 1) water pollution that may reduce fish diversity in water bodies, 2) evaluation of the effects of serious environmental events on local aquatic communities, and 3) tracing the target species such as indicator, protected, and endangered fish in the river system. Our results demonstrated that the environmental influence on fish distribution and composition analysed by the eDNA method showed a similar tendency to that analysed by the traditional method (e.g., individual number and biomass), suggesting that eDNA is a useful tool for monitoring biological communities in the field. In this study, DO, velocity, salinity, depth, CODMn (or BOD5), and the bacteria amount in the water were the key environmental factors that influenced the fish communities. In fact, given that fishes are not only the crucial components of the local food web, but also the high-level predators that exhibit top-down control effects, key environmental factors that influence fish distribution and composition may also influence food web properties (e.g., ominivory, connectivity and stability; see Wang et al., 2018a; Wang et al., 2019b; Wang et al., 2021a). Our further research will focus on the eDNA-based relationships between the attributes of fish communities and those of invertebrate communities as well as on the structure and functioning of aquatic food webs.