Bluegill

The Bluegill (ブルーギル, Burūgiru) is a very inexpensive fish found in the river. Despite being uncommon, it sells for the second lowest amount for any fish, 120 Bells, losing only to the jellyfish. It can be found in the river.

Donating to the Museum
Blathers will give a speech on the bluegill when donated to the Museum:

In City Folk
"...Ah, hoo, the bluegill, scourge of fishermen everywhere. Once introduced to an area, this fish will eat up many of the indigenous breeds, eh wot? But with a face like that, it's hard to believe our wee fishy friend here has any bad intentions..."

Encyclopedia Information
Once the player has caught a particular fish or bug, they can find information about it in the bug or fish menus. Once the bluegill has been caught, the following information can be found in the fish menu:

Further information
Of tropical sunfish body shape, the bluegill's most notable feature is the blue or black "ear", actually an extension of the gill cover called the opercular flap. Its name, however, comes from the bright blue edging visible on its gill rakers. Also called the bream, this fish tastes nice. It is very common and often fished. Catfish, Bass and turtles prey on the bluegill.