Researchers in Osaka Prefecture, western Japan, have confirmed for the first time that endangered Japanese eels inhabit Dotonbori River in the middle of Osaka City.

The prefecture's Research Institute of Environment, Agriculture and Fisheries says researchers checked the river last November to see if any eels dwell there.

They caught 11 Japanese eels, designated as an endangered species by Japan's Environment Ministry and international bodies.

The eels measure 30 to 60 centimeters long. The largest one is on display at the institute's facility in Neyagawa City.

Eels are found in rivers throughout the prefecture, but it is the first time that an academic survey has confirmed their existence in Dotonbori River. Its waters flow through one of the busiest dining and entertainment districts in the city.

Institute researcher Yamamoto Yoshihiko says the finding of eels points to the existence of an ecological system with small fish, shrimp and crabs on which eels feed. He says this means Dotonbori's water is much purer and less polluted with sewage than before.