Yeah, that's why it's nice to get pregnant females and let them drop some fry from whatever males were in the tank with them at the store. As to males, watch the tank and, excuse my terms, pick the horniest male out of the whole tank, he'll be the one who will not leave any of the females alone. As to inbreeding, it can be prevented but it takes a few tanks to do it, unless of course you have some bigger fish who wouldn't mind a snack when you need to get rid of some...