I think it depends on how big your bgk is and what its personality is like. My bgk is very peaceful and it hasn't harmed any of my fish that weren't dieing. I have reason to believe he may have eaten my oto one night but the oto was dieing. If any of my fish swam into his cave he would nudge it with his nose and the fish would leave. I think he will eat ghost shrimp but other than that he hasn't harmed my other fish. I've read on the internet that some are agressive but mine isn't. I have had guppies, swordtails and fish about that size with him but now harm came to them. If yopu look at my signature you will see what I have with mine now.