Like mentioned above, from my experience, when crappie are suspended together, they look like thin, vertical footballs, and sometimes, when they're moving, they look slightly thicker, or can look a little broken up, like the signal has static. Garfish will look similar when facing you, but of course, once they turn sideways, they get much longer. Same thing with catfish; and I've noticed that the catfish I've caught when I thought I was looking at crappie, move much more in circles. Bluegill look almost round, and move a lot more than crappie do, too.