Generally around sexual maturity. Plus depends on personality, tankmates, temperature, and if your trying to pair. My previous experience with festae was at 5-6" the sub-dominent male kept to himself and out of. The others way. The dominent male didn't pay attention to any fish in the tank except for the females. The females would. Chase but not beat up everything in the tank they only fought eachother to impress the male. They were in a 180 with some gt's, Texas,and convict.