4.3 Biomarkers that can distinguish the differences between fish
communities
The LEfSe results showed that biomarkers selected by both eDNA and
electrofishing exhibited similarity in headwaters and lower reaches but
differences in middle reaches. eDNA could identify the fishes of
Danioninae, Siluridae, Nemacheilidae, Oxudercidae, Acheilognathinae, and
Barbinae, indicating that eDNA has a high degree of recognition for
rheophilic fish living in headwater habitats. With widespread rapids and
riffles, rushing waters in headwaters had a great perturbation effect on
DNA remaining in the environment, especially for those deposited in the
sediments. Thus, the eDNA samples collected in rapids (e.g., sites L1 –
L2 in the Liuxi River and Z1 – Z3 in the Zeng River) contained more
species OTU information than the eDNA samples collected in slow-flowing
or limnetic waters of the middle and lower reaches.
An interesting finding was the difference between eDNA-based biomarkers
and biomass-based biomarkers. The biomarkers selected by LEfSe through
relative biomass preferred to screen out species with larger body sizes,
such as Xenocypris, Squaliobarbus, and Pterygoplichthys in zone
IV and Ictalurus and Rhabdosargus in zone VII. This is a
problem that limits the promotion and application of eDNA in a wider
research area. As suggested by Rourke et al. (2022), key influencing
biotic factors on eDNA effects included the taxon examined as well as
their body size, distribution, reproduction, and migration.
Nevertheless, there is considerable evidence to support using eDNA as an
ancillary tool for assessing fish population abundance and/or biomass
across discrete spatiotemporal scales, following preliminary
investigations to determine species and context-specific factors that
influence the eDNA abundance/biomass relationship (Bylemans et al.,
2019; Doi et al., 2017). Advantages of eDNA monitoring relative to other
approaches include reduced costs, increased efficiencies, and nonlethal
sampling (Stewart, 2019).