It's much easier to do around the time of the spawn. Males will have an "ear tab" that is as long as it is tall. A female's ear tab will be taller than it is long and appear more as a thin crescent. Males breast color is more rusty-red, while the females will be a breast color of yellow, orangy-yellow or just pale. Bigger fish are easier to identify as well. Even trained biologists are not always correct in their gender assessment, but the more you've done it the better you'll get.

Holding a redear sunfish is like running with scissors.