Char

The Char is an fish that can be found in the waterfalls. It appears in March to June, from 4AM to 9AM and from 4PM to 9PM. It will appear again from September to November to 4AM to 9PM. When selling it to Re-Tail, the player will earn 3,800 Bells.

Location
The Char is found in the waterfalls.

The Museum
The Char can be donated to the museum. Upon doing so, the following text is given by Blathers:

"Char are related to salmon and live in rivers upstream, not generally migrating to the ocean. They prefer colder water and dwell in secluded, clear rivers deep in mountain ranges. Since they tend to hide mostly in between rocks in these cold areas, they can be rather difficult to spot."

Quote
Upon catching the fish, the player will say the following:

"I caught a char! How bizarre!"