I found the game to be largely confusing. Half of the UI was cut off at the top of the screen so it was hard to make out how much health I had. Though my health never went down at all until the very end when I sat back and just let the fish spawn for a minute without me doing anything. That was the only time I ever saw the poison clouds spawn, though I'm still not entirely sure what causes them to spawn. The models and textures are nice though for such a short period of time.
Viewing post in Dead Fish Cleanup Simulator jam comments
I added upgrades just before deadline. And upgrades are necessary, you can't continue without them. So, the balance is totally broken.
If you want, you can try again and pick only two upgrades: poison and size (or speed). Don't pick fish speed. In this case, the game is more looks like what it should be.