Goldfish are a type of fish.
Like all types of fish, each goldfish gives one fish fillet when caught.
Goldfish can only be caught with gold lures in fishing spot #11 (the deep water area surrounded by rocks).
Goldfish can be caught in small circles and therefore are harder to catch.
See Fishing List for more detailed information.
Goldfish in the fishing book
The goldfish is on page 21 of the fishing book:
Even the emperors of ancient China revered the beauty of the goldfish.