most people tell by the body shape and fins. males tend to have bulky body structure as well as long top fin. females tend to have a bit more rounder top fin. another way you can tell is flip the fish upside down and look at the anal gland. correct me if im wrong but females have a U shaped anal gland and makes have a V shape. and most female fh's do not grow humps on their head. or if they do then it wont be as large as the males.