Perches are a type of fish.
Like all types of fish, each perch gives one fish fillet when caught.
Perches can only be caught with green and blue lures in fishing spot #12 (the shallow area with dragonflies and poles).
Perches can be caught in small circles and therefore are harder to catch.
See Fishing List for more detailed information.
Perches in the fishing book
The perch is on page 23 of the fishing book:
This introvert fish enjoys the calm atmosphere of still waters.