We used to buy bulk baitfish to give to my dad's Parana. Most of them they'd eat, but every so often we'd get one or two bluegill that just decided they were parana. They'd all move in a pack together, the bluegill would help the Parana hunt, it was crazy.

The wildest thing was eventually the mixed school would eventually start to turn on the smallest as the food fish dwindled. Straight canibalism on the part of the bluegill. Sometimes the bluegill would be too big for the school to finish, so they'd eat the back half and the front would still be swimming with the gang like it wasn't just yesterday's dinner.