I've seen pickerel attack fish that were on the line (or attack just after the fish came unhooked), and I've had bass and pike come up and look the fish over while I was bringing it in, but I never caught one that way.
There's a place where I fish in the springtime where I see BIG bass chasing bluegills in the outflow from a culvert. I haven't tried to tie a bluegill fly yet, but I know bluegills are near the top of the menu for bass. I've caught lots of bass (even small ones) that had bluegill tails hanging out of their gullets.
Anyone got a good bluegill pattern?