Short and sweet.
I like how the different mechanics are introduced, and how each level flows into the next. I like how you foreshadow future hazards like the red fish that you see early on in an unreachable part of the level - very well done.
This reminds be of the balloon levels from Mappy.
Some critiques.
- The music is quite grating - this may just be a 'me problem', but if the game was longer than a couple minutes, I probably would have turned off the sound.
- In general, more sound effects would be nice. It would help sell the underwater vibe.
- I would like to see some more variety in movement, both in the player character, and the creatures/hazards around you. Adding some acceleration/momentum and some animations to the creatures' movement would go a long way.