Challenging, but fun.
Second boss could have some visuals, where it will spawn his ghost thingies (the ones he spawns randomly), cuz you can by accident swim into it and it will be kinda not your fault, because you weren't aware where it would spawn.
And third boss fight was a bit mess tbh, it felt like it spawns a lot of his stuff and it is hard to tell where is the safe spot, so I would add some color indicating for attacks there. For now for me it felt more like you survive on this boss not cuz of your skill, but cuz of random, but perhaps I didn't find the right strategy for it