The fish is a little hard to control. I thought the clunkiness of the controls where it doesn't immediately turn diagonally was because of a tank control scheme initially, so I was surprised to hit the A key and see it go straight left. The rocks were also a bit annoying, since the fish easily gets caught on them and it forces a direction change, and there are also places where the gap is too narrow to pass. I enjoyed the game regardless, because it was fun to evade the enemies. And it was clearly worth it because of the weird fish mating ritual, of course.
Minor note, I don't think the continue button on level 4 works (it's grayed out) so I wasn't completely sure whether to play level 5 or not from the menu, since it was accessible there.