[Feathers]

Well, with my mollies, once they got settled was when they started nipping around to establish their hierarchies. I'm not terribly familiar with Tetras, but it might be possible that's a little bit of the same thing? I've read that Danios will nip at fins as a behavior that they're under stress.

I'm not too sure though! Maybe someone who knows more about the little fishies will come help you out. I'm still learning about them, myself!