Background

Environmental DNA (eDNA), which has become useful tool in biological survey in recent years, is particularly effective for research on rare and endangered species because it does not capture living organisms.

Environmental DNA is also has been introduced in the investigation of Japanese eel, which was registered as an endangered species (EN) by the International Union for Conservation of Nature (IUCN) in 2014, but various things must be concerned before applying this new technique on study of Japanese eel.

Japanese eel is migratory fish with a complicated life history. Also it has large variations in morphology and physiological condition depending on the growth stage.

Takeuchi et al., 2019 reported that the eDNA concentration increased as the grew and upper developmental stages, while the body weight ratio concentration decreased, in Japanese eel.

In addition, it is known that Japanese eel has large individual differences in size even at the same growth stage, and its behavior affected by environment (e.g. Japanese eel stop eating and rarely moving when the water temperature decreased in winter). These can cause the eDNA concentration as DNA emission to water changes.

In this study, variations of eDNA under sequentially changing rearing conditions was investigated using the same individuals of Japanese eel.