Rainbowfish are a type of fish.
Like all types of fish, each rainbowfish gives one fish fillet when caught.
Rainbowfish can be caught with green and purple lures in any fishing spot, but their favorite spot is #8 (the rocky area near the fishing boat).
Rainbowfish can be caught in medium circles and therefore are a bit harder to catch.
See Fishing List for more detailed information.
Rainbowfish in the fishing book
The rainbowfish is on page 5 of the fishing book:
The appearance of this lagoon fish in your lake shows what a wonderful habitat you have.