Love it. Very satisfying when you slap the ball over to the opponent's side and finally get to watch the them struggle a bit. I can totally see how it would be a blast multiplayer (if only I had any friends).
Remappable controls would be really nice, but is admittedly a big ask for a jam game. If you have plans to work on this more, both that and controller support I think would really make things pop.
Overall, however, I find the difficult controls and the silly physics very charming. Really gives the game a good goofy vibe. It's not always the case with game jam submissions, but with this one I could totally see a full game where you just flop and flip fish around in a pointless attempt at a legitimate volleyball game, haha.