Crimson Tigerfish

This is the catch that turns a crimson lake into a potion supply. Heartreach is the reason to bother: it drags hearts toward you from across the screen, which quietly solves the problem of a dropped heart landing in lava or behind a wall in the middle of a boss fight. Melee players standing in the enemy notice it least. Anyone kiting at range notices it a lot.

Crimson water is easy to fish once you have cut a hole down from the surface, and the bite rate is generous enough that one evening covers an entire boss run. Bank the spares, since the same fish also goes into the big cooked meal.