Japanese eel, Anguilla japonica.

Environmental DNA contributes to locate endangered eels

JAPAN
Tuesday, March 26, 2019, 00:20 (GMT + 9)

Research performed by a group of scientists reveal that environmental DNA (eDNA) analysis from small samples of river water makes it possible to perform faster and more effective surveys of Japanese eel populations, which could help to conserve this endangered species.

Japanese eel bury themselves in roots of riverside vegetation during the daytime (Photo: kobe-u.ac.jp) ►

This rapidly-advancing eDNA technology can monitor aquatic lifeforms through extraction and analysis of DNA present in water, without capturing the organisms themselves.

To determine whether eDNA analysis could be used to show the distribution of Japanese eel (Anguilla japonica), the scientists collected 1-liter samples from 125 locations upstream and downstream in 10 rivers in Japan, and analyzed the eDNA from these samples using a Real-Time PCR system. At the same time, they carried out an electrofishing survey in the same locations, and compared this with the eDNA analysis results.

Japanese eel eDNA was found in 91.8 per cent of the locations where eel had been confirmed using electrofishing (56 of 61 locations), and eDNA was also detected in an additional 35 areas (mainly upstream) where eel individuals were not found.

According to the reserachers, this shows that eDNA analysis is more sensitive than conventional surveys for detecting the presence of Japanese eel in rivers.

Comparing surveys: sampling investigation using electrofishing (left), water sample for eDNA analysis (right).(Photo: kobe-u.ac.jp)

Electrofishing data for eel numbers and biomass also positively correlated with eDNA concentrations, showing that eDNA could help us estimate the abundance and biomass of Japanese eel.

In this study, electrofishing required three or more people for each river and took at least three days. Collecting water samples for eDNA analysis only needed two people, took half a day at the most, and data processing was finished by one person in one and a half days. When carrying out a large-scale distribution survey the eDNA analysis method is better in terms of human and time resources.

Correlation between number of Japanese eels and eDNA concentration in rivers. (Photo: kobe-u.ac.jp)

This study, published in Aquatic Conservation: Marine and Freshwater Ecosystems, was carried out by Research Associate Hikaru Itakura (Kobe University Graduate School of Science), Assistant Professor Ryoshiro Wakiya (Chuo University), Assistant Professor Satoshi Yamamoto (Kyoto University), Associate Professor Kenzo Kaifu (Chuo University), Associate Professor Takuya Sato and Associate Professor Toshifumi Minamoto (both from Kobe University).

Itakura comments: “Concentration of eDNA in rivers is influenced by physical properties such as water depth and the speed of the current. Next we must increase the accuracy of eDNA analysis by clarifying the impact of these physical properties on eDNA concentration.”

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