2025 Volume 81 Issue 16 Article ID: 24-16210
In recent years, many ecosystem-friendly revetments have been installed in small and medium-sized rivers as Nature-oriented river works. One example of such revetment is a frame revetment that is porous to provide habitats for aquatic organisms. A salt marsh is also important as a habitat in an estuary. In this study, we conducted an environmental DNA survey of Japanese eels and observed the frame revetment using an underwater camera to observe fish behavior.
The results showed that fishes such as Japanese eels and Chichibu goby were using the frame revetment as a resting and feeding site. The environmental DNA analysis results showed that the environmental DNA of the Japanese eel at the bottom of salt marsh was not detected during hypoxia, and it was detected before and after hypoxia. On the other hand, environmental DNA concentration at the frame revetment and surface increased during hypoxia. This suggests that Japanese eels temporarily changed their habitat from the bottom of salt marsh to the surface of it and estuary frame revetments in response to the hypoxia caused by rainfall and tidal changes.
