Seeing as fish are in development, here's an idea for a interactive non-spear fishing implement.
The cast net, a net with a central handline and weighted edges made for throwing:

A cast net would be used by throwing outward in an arcing movement, travelling a short distance and trapping or entangling fish that end up underneath it, then recovered along with whatever's caught in it by drawing back the handline.

In terms of in-game representation, it would immobilize or greatly limit the movement of fish or other smaller mobs trapped in it, and thus allowing the player to more conveniently dispatch or capture any such trapped mobs.

It could also potentially be used for snaring and entangling larger mobs, in order to slow them down for combat, or just to make unruly mobs a just a little bit easier to handle.