This fish is called "kawanago", but it doesn't look like anago.
In fact, they are close relatives of gobies and donko, and if you ask me, they are somewhat similar.
It is said to be distributed from the downstream of the Pacific side south of Ibaraki Prefecture to the mouth of the river.

Many parts of its ecology are unknown, and it is classified as a "rare species" in the Ibaraki Prefecture Red Data Book.

It often stays still as if snuggling up to a stone or tree, so if you are in a good place, you can observe it carefully.

Please take a look at the slightly rare fish, kawanago.

Exhibition place	“Downstream Nature” aquarium (4th floor connected waterside zone)