never bred them, have had 2 in a 40B with my darters and neither of them are fin nippers in my experience, at all. my mosquitofish was a bigger bully than them. Sorry I don't have breeding info, but I can tell you they tend to stay motionless in the water column or on the bottom most of the time, so if you are seeing some type of behavior different than that between several of them, you either have a territorial dispute or breeding posture lol.