Chum Bucket

Thrown into a pool it raises your fishing power, and the bonus lands at the very end of the calculation, so unlike your rod and gear it is not scaled down by time of day or weather. That makes it worth the most exactly when everything else is working against you. Three floating at once is the ceiling and a fourth does nothing.

Every time you pull the line back it burns a little life off every bucket in that body of liquid at once, whether or not you caught anything. Casually fishing over three of them wastes them fast. Pair with a Sonar Potion and only reel when the thing on the line is worth having.

Spawning. Chum on the surface pushes ocean floor shark and orca rates up sharply, and the game traces line of sight upward from the spawn point to the chum, so a sealed pool suspended above the ocean will not trigger it. Left alone without fishing, one throw lasts a long time, which makes this the cheapest shark farm available. Blood Moon fishing hands them over in bulk, so supply stops being a concern after one night.