Its always a possibility, but as Mann points out, they aren't that big, and it would be a tiny little nip at best. Between my new kitten, and my tank full of Colombian's and Knight Goby's, I'd much rather get nipped by the fish anyday
. This is just one of those potential incidents when keeping any animal. But as others have said, so far, my fish just run away from my hand, as they are all quite skittish. Depends on the fish, and their own disposition I suppose. Everyone will have different experiences here.