I have a 6 inch Blue Dempsey and a 9 inch Blue Dempsey. Both are males. They co exist pretty well together. From my experience keeping them, they only show aggression if kept with other cichlids and if they're the dominant fish. If they aren't the dominant fish they become very passive. Almost to the point of not defending themselves. I've also kept them with non cichlids with no problems at all. They should really only be kept with mildly aggressive cichlids. They're just not as tuff as the regular Dempsey. They do grow slow and are very delicate under 4 inches as posted earlier.