I've gotten 6 new fish just yesterday, 4 gold and 2 black. They were eating and swimming fine, until one of the black ones decided to chase the other gold ones around. It looks very stressful for the fish and me, as i don't want either of them to be chewed up or dead. The black one seems to just be chasing after the other golden ones, especially the one that doesn't seem to be swimming that fast. And I don't mean that it is chasing from a distance away. The black one is literally sticking to the butts of the other fish. If I'm not wrong, there seems to be nipping involved, but most of the times I'd say it's biting/pecking, as it's not a gentle nip. Could it be bullying? Not enough food? But if it was the latter, shouldn't it go after the other black fish, too? I'd like to know if I should separate them or not, appreciate any and all help.