Cool game! I really like the concept of the game, and it's awesome that you got co-op to work! I like the way you use a single resource to power the whole game: fish are the weapons, the healing, and the money generation mechanic. I kind of got the same feeling I get with Animal Crossing and a lot of other games of wanting to optimize my path. I wanted to catch as many fish as I could, but not too many (so I could go get upgrades and hopefully catch them even faster). I wanted to sell all the fish I could to get more money, but not all of them, since I needed to fight slimes. I think it was a cool way to punish being greedy with your fish :b
I think one thing that could be improved about the game is some of the controlling. The camera, for one, has a nice sliding effect, but allows you to move too far off center. I appreciated that you guys took the time to get a smooth camera follow, but the player should still be relatively centered, otherwise it's hard to see where you're going! Also, I thought the controls were a little unintuitive. I'm used to touch typing, so I have my index finger on J usually. It didn't make too much sense to me to have to hit H to attack. I think I would have preferred the buttons JKL; instead of HJKL. It also makes it easier for me because I can switch fish with N and M with my index finger while attacking with K, rather than trying to control H, N, and M all with my index finger.
Overall, great concept; I think y'all could go pretty far with this if you wanted to continue with it post-jam :]!