Asps are a type of fish.
Like all types of fish, each asp gives one fish fillet when caught.
Asps can be caught with purple and gold lures in any fishing spot, but their favorite spot is #8 (the rocky area next to the fishing boat).
Asps can be caught in medium circles and therefore are a bit harder to catch.
See Fishing List for more detailed information.
Asps in the fishing book
The asp is on page 7 of the fishing book:
This large solitary fish used to like school trips, but now prefers his own company.