Bluegills are a type of fish.
Like all types of fish, each bluegill gives one fish fillet when caught.
Bluegills can be caught with blue and gold lures in any fishing spot, but their favorite spot is #2 (the reedy area with some water lilies).
Bluegills can be caught in medium circles and therefore are a bit harder to catch.
See Fishing List for more detailed information.
Bluegills in the fishing book
The bluegill is on page 5 of the fishing book:
This is an amazing specimen with sparkly scales and a graceful swim.