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. Unlike the crucian carp, it only appears form 9 am to 4pm.

Donating to the Museum
Blathers will give a speech on the bluegill when the bluegill 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..."

In New Leaf
Blathers gives no specific speeches once the bluegill is donated, but he posts a description for it.

"Bluegills have spikes on their dorsal fins to help protect them from enemies and harm. Their offspring actually have a fairly high survival rate when compared to other fish. The males chase away the females and take over protecting the eggs and babies in the nest. Although bluegills are small, they are actually related quite closely to the black bass."

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.