My friend had a male betta with danios and they nipped the betta's fins so she had to seperate the Betta, but other people have no problems. My danios are a bit nippy so I dont keep them with fish that have long fins. I heard with nippy fish like danios or barbs, it is best to keep them in a school of 6+ and they dont tend to nip other fish. I had 6 tiger barbs who are apparently notorious nippers and I never had a problem