Interesting game
The upgrade system gives some depth. and the fight with the fish feels satisfying. For game jam time frame it's quite nice, but just a little more upgrades would make the game even more fun.
Also, please, make the fish follow you better when you are far from them (especially in the first wave) or just limit the player movement space, since at the beginning I lost the fish and got softlocked and if not for the comments about the game, I would've left it there unsatisfied.
Overall, the game felt really nice.