On June 16, I visited the Salmon Hometown Chitose Aquarium.
One of the highlights of this aquarium is its underwater observation windows, which allow visitors to look directly into the real waters of the Chitose River.
According to the staff, from early to mid-June each year, large schools of Japanese dace (Ugui) gather here during their spawning season. This year, the number of fish was especially impressive.
In addition, I was able to observe the Jūsan Ugui, a species that has rarely been seen in large numbers in front of the observation window during previous spawning seasons.

I filmed this rare and fascinating scene this year—please enjoy the video.

2025.06.16 – Schools of Japanese Dace During Spawning Season (Chitose Aquarium) | Kawatabi Hokkaido (YouTube)
https://www.youtube.com/watch?v=wqVeHgnU7N0

At the Chitose River Underwater Observation Window, visitors can see three species of Japanese dace.
Ugui, Ezo Ugui, and Jūsan Ugui.

This large school is likely made up mainly of Ugui and Ezo Ugui. Ugui are known to form dense schools when spawning.

This fish is the Jūsan Ugui, identifiable by a single reddish line along its belly. It is strikingly beautiful.

Salmon Hometown Chitose Aquarium – Map Code: 113 889 586*51