It's a nice relaxing puzzle game. It's not difficult by any means as the player can impose their own level of difficulty. One player may want to reach the meet-up spot at the same time, while another one can be happy to trap a fish at the end, then move the other fish. The music helps to add to this relaxing atmosphere.
I think grid based movement might be something to consider for this game. On one hand it'd add to the puzzle element and make the game feel like movement has to be more thought out. On the other hand it might detract from the relaxing feel of the game since movement would be jumpy rather than smooth. It'd be up to what aspect of the game you want to focus on more.
Great job, it gives the feeling of watching a koi pond!