I had them breeding at about 2 inches. Believe me if you have a male and female you will know when it is breeding time, lol. Their first brood was actually very successful. Good parents and I hope that there aren't other fish in the tank. They can be nasty devils when guarding fry. They use to come up and bite my hand when I would do something in the tank. It never hurt but always scared the @#!@ out of me. Fun little fish though, good luck!!