One BIG problem.
Collisions are detected for the player's fish and the enemy fish when their bounding boxes (rectangles which fully contain their respective sprites in their dimensions) touch. This results in the player's fish being able to eat fish that are several pixels away from the actual sprite (and conversely, be eaten by larger fish that seemed far enough away). That big bug is enough to drag your score down.
But I'm not totally heartless. I think this game has great potential. The graphics and sound are very well done, and the idea of making the fish robotic was very creative. In fact, if you fix that bug, I'll be willing to give you a review of 10 for your game. Alert me via e-mail if you get around to it, and I'll look at the new and improved version.