This is a list of all the fish by shadow size.
The sizes of these shadows are smaller than your fishing bobber. Most tiny fish are considered rare or uncommon.
Small fish shadows are about the size of your bobber.
Small (trash & other items)
These ones are slightly bigger than the small shadows.
These large shadows are about the size of your body.
These fish shadows, implying the name, are very large. They are about the size of your entire character.
Very Large (trash)
Long & thin
One of the most distinctive fish shadows, very, very few fish have this shadow.
These shadows are noticeably longer and more slender than Very Large fish. All Huge fish are rare and have a decent selling price.
Huge with fin
These are the largest (catchable) fish shadows. All fish with these shadows are part of the shark family, are rare, and sell for a fair amount of Bells.
There is only one fish (mammal) in this category: the Whale. It is bigger than Kapp'n's boat and cannot be caught without an action replay code.