A simple game that might have gotten tedious very quickly, but the elements you've added to include some variation helped spice things up a bit.
There's still a bit of tedium to it after 20 or so volleys; I would have liked to see some scaling of difficulty as the points got higher. Also would have liked to see some randomness in the AI bot's behaviour. At present, it merely acts as a wall, rather than a separate party with their own decisions to make.
I should add, the bizarre sharks and cannonballs and on-fire volleyballs really creates a joyful atmosphere that is well mirrored by the music. And the animations of the fish are beautiful.
Overall, a nice game. Well done.