I'd like to see the fish changed into a mouse-follower. Or at least add some friction to it's speed.
You could make the enemy-movement more diverse. (and maybe slower, this looks a bit unnatural)

Other than that it looks great and it could be a very addictive game.
(Allthough it's just as creative nowadays to make a fishgame like this as making pong or breakout back in the days.)