I think it is hit or miss will. I kept trying to keep a pair, but one kept killing off the other. I found out that two males don't tend to tolerate each other and the only way to keep more than one was to keep a group. and/or figure out a way to tell the females and the males apart. (BTW, the last one I thought was dead, he was living in my overflow for over 3 weeks, so you gotta figure he was living with little food and seemed healthy, if not beat up. I have since moved him to lisa's tank.