I have my BGK with danios as well. Very small danios. So far, he has yet to even bother a single fish in my tank, though when any of them goes inside his hollow stump, they get kicked out promptly. He even does this rather gently. He doesn't even bite them or anything, just pushes them out with his head. He has done this to all my catfish, (banjos, cories and a synodontis). I keep him well fed on tubifex worms and other foodstuffs, so that might have something to do with it. That and he's only about 5 in long.