When I had my all male hap tank, there was some mild aggression but nothing that really got out of hand. Overcrowding them reduced that aggression alot but there was usually still a fish that really didn't like one other fish and the occasional chase occurred. Introducing a female into there would be a big no no unless you wanted to witness some carnage. LOL. If there was sufficient overcrowding, the female might go unnoticed. My tank was never that overstocked to that degree. I've seen some tanks where it was just a huge mix of both M and F African cichlids and there was little aggression due to the sheer numbers. However, all fish are different so you just never know.