Every fish in the ocean may be happy, but not you, you're not happy.
The concept alone was enough to keep me entertained for a while. xD
A couple issues though:
The visuals look great; the fish textures in particular are a great piece of work for a weekend. Did you make them from photos or something? The depth of field really contributes to the sense of scale and oppressive atmosphere.
I found the controls difficult to use, and the camera is way too sensitive. This, combined with the lack of feedback about where you're actually aiming, made it hard to hit anything, and I kept being swarmed and dying.