Environmental DNA Analysis in a River Detected a Possible Distribution of Fish Species Difficult to Capture

Environmental DNA (eDNA) analysis is a biological survey method that has drawn much attention in recent years. However, the results of eDNA analysis and capture surveys often do not completely match, and the validity of the eDNA analysis needs to be verified. Verification of eDNA metabarcoding was conducted in a river in Fukushima Prefecture, Japan, in comparison with capture survey data. Most of the captured species were detected, and 13 uncaptured lineages (two genera and 11 species) were detected in the eDNAs. Some rare species detected in the eDNAs were also identified, including exotic eels and an endangered yet out-of-range bitterling fish. To confirm the validity of the exotic Anguilla spp. detected in eDNAs, mitochondrial Cytb sequencing was performed on captured eel specimens. All eel specimens were sequenced as the native Anguilla japonica, indicating a small biomass of the exotic species difficult to capture. Our results clearly indicated the eDNA analysis as a powerful tool for detecting possible habitats of rare fish species without disturbance to the natural environment.