Fisheries management in my college days...though I never finished my degree. You could also assume any fish over a certain size is female as well, especially in warmer fertile waters. 3 lbs. isn't really big enough to make that assumption, especially in SC. I've often read that you can vent sex them, but I have never been able to tell the difference. I will also say, males create nests. When spawning is over, the female leaves. They often find another male to spawn with. They do get damaged tail fins, but it isn't from fanning. It is from the male nipping during the spawning fervor. Males remain locked on the nest to fan the eggs with their pectoral fins, not their caudal (tail) fin. From all this evidence, it sounds like you saw a 3 lb. male creating a nest.