Yay, finally I've been "lucKey" enough to test the game! Liked the graphics a lot, but can't hear any sound or music. Maybe I'm missing something since I cannot make my fish swim at a good pace. Anyway I tried until eating all the shrimps, but nothing more happened? Is there an ending condition? The mood is great, overall, and plenty of open-source tools used. Nice job.
Since sound is currently the main thing through which you get feedback on the accuracy of your timing, playing without makes it harder to win.
The best moment to hit a key is when you are about 3/4 on the way to a square, once for each sqaure that you move. The swimming animation will more clearly hint at this moment in future versions.