For some reason my browser doesn't want correctly focus on the game, meaning that spacebar scrolls the page which makes the game unplayable for me. I don't know why this is, so far your game is the first where I have this happen.
(And no, I didn't rate your game that would be kind of unfair.)
edit: pressing `F` will get it into fullscreen mode. HOORAY! I CAN PLAY!
So, feedback time:
First, what I think is a bug: when in this mode the character jitters A LOT.
I like the visuals, music and sound effects. I am not sure of the theme though. The idea is fun and all but in a way the fish is just a normal thing to avoid. Replace the sprite for something that is normally bad and you have a game that works exactly the same but doesn't follow the theme.