4.1 The eDNA-based distribution and composition of fish
communities in rivers
The fish species detected by eDNA across the 38 sampling sites contained
all the fish species sampled by electrofishing, indicating that the
capacity of eDNA to find species was stronger than that of
electrofishing (also see Balasingham et al. (2018; Beng and Corlett
(2020). Generally, the extra species detected by eDNA were the species
that have been reported in the Pearl River system but were not
distributed in the designed sampling sites of this study. This indicated
that on the one hand, eDNA could trace the DNA released by fish species
that were difficult to sample by traditional methods; on the other hand,
the DNA of these hard-catch or rare fish species might be carried by
upstream or tributary waters and then collected at downstream or
mainstream sites. Therefore, eDNA in water reflected more information on
species distribution than the traditional method. However, eDNA contains
more extraneous species information than traditional in situ field
monitoring, which confuses
site-specific assessments of ecological health or biological integrity.
In fact, the similar spatial distribution pattern shown by NMDS and the
high regression coefficient between eDNA- and number-based diversity
indicated that eDNA could reveal the core information on the composition
and diversity of fish communities as comprehensively as those reflected
by individual number and biomass collected by traditional in situ
investigation. Therefore, we suggest that researchers and managers use
eDNA as an ecological tool to identify fish community structure and
associated environmental factors.