I think this is a good start, but it needs a lot of work. A LOT of work..
First of all, animate the fish. Add some style to your work, don't settle for what's easy to render. Go the extra mile in character design. The second I saw all of the fish, in their flat colors and static animations, I got extremely bored.
I would reconsider the background track you use, or at least give players the option of changing the music. That song became annoying in about 3 seconds.
I would also add more to the game play. For example, add some powerups, items, different kinds of enemies. There should also be a level progression.
Like I said before, this is a good start! It just needs a LOT of work.
Good luck! :)