I've noticed something about sunfish. If you have a sunfish on a hook, it freaks out and dashes around. If you put your hand around it, keeping it in the water, it tries to get away. It does the same if you take it out of the water. But if you hold a sunfish underwater, tilted considerably to the side or held on its side, it flares its fins out and goes perfectly still. Out of 15 bluegill and longear sunfish I caught during one session (two people with fishing poles and one trap in the water), about 10 of them had to be handled for some reason. All of them showed the same behavior when gently tilted to one side. I didn't need to apply much pressure, I just had to gently cradle the fish about an inch below the water's surface, using my fingers as a bit of a cage to keep it from righting itself. Aside from tentative little tail movements in an effort to get right-side-up, the sunfish didn't fight.
I tried that on a big shiner I'd caught on a hook, and it didn't help much. The shiner kept flipping out.
Do sunfish just get disoriented if you tip them sideways, or what? Is it a mouse-like "OMG, I'm caught, must play dead in order to not be interesting" reaction?