Reminds me of E.V.O.: The Search for Eden.
I really like the expressions of the fish and the backgrounds "near" tiles (ie. the back of the cave wall and seaweed). However, the yellow walls just look ugly to me, and the far background doesn't look very underwaterish due to the orange. Some shafts of light might help to symbolize the underwaterness of it all. The desaturated orange makes me think the fish are in some kind of toxic water or something. I do like the yellow hilights on the back wall, though. There's something about the jellyfish that I don't like, but I don't know what it is. Maybe it's the lack of a definitive hilight.
Anyway, this is lookin' cool, and I would like to play a game like this.