Over the last few years we have had several bettas and there is about a 50/50 chance that if 2 females are kept together there will be aggression. I have also seen aggression more frequently when it has been a male and female as the male gets mating "ideas" and often becomes very aggressive and relentless presues and nips at the female and I have seen death on several occations. With more than one female then like I said you have a 50/50 chance of aggressive behavior. I guess it just depend on the individual fish. That is my experience with them anyway.