From Nookipedia, the Animal Crossing wiki
The Bass is a fish that only appears in Animal Crossing. It is a common fish that sells for 300 Bells at Tom Nook's Store. It appears in the river and is the same species as the Small Bass and the Large Bass.
Donating to the Museum
Blathers will give a generic comment about it.
"This is one of those fish that seem to mysteriously disappear from time to time. Drives fishermen batty, wot! Have no fear, dear friend! You're leaving this beauty in very good wings, hmmm? Hoo! Owl humor. Hoo hoo!"