i have 5 cucban cichlids between 1.25" - 2" in a 55g grow out. one of the biggest has turned really dark around the face and belly area. its also the most aggressive. is this a male thing or female? i looked at alot of adult cubans and it seems to me that the females are the darker ones. all the other ones are still grayish white. what do ya'll think this is due to?