Guys, he wants a datnoid. While I agree that a 155 isn't large enough to hold one of the larger datnoid species, the American/Silver Datnoid is about the only species that a 155 can hold for life and likely only up to two or three. The silver dat maxes out at 12 inches and since the rule of thumb is to get one datnoid or 4 or more, I think the best option is to get one silver dat and a similar-sized, mildly aggressive cichlid like a severum. Putting four 12-inch fish in a 155 for life with silver dollars and a BGK is crowded. I'd say just get one silver dat, one severum or similar sized cichild with the same temperament (avoid oscars or anything more aggressive than oscars), 4-5 silver dollars and a BGK. I don't know if I would trust any spiney eel save a fire eel or tire track eel with a datnoid. Smaller eels like the peacock may end up as lunch one day while both the fire eel and tire track eels will get to 3 feet. A 155 is too small for one of the larger eels as well. Come to think of it, there is a smaller spiney eel that grows to 28 inches and resembles a tire track eel. That's big enough to live with the datnoid. Maybe that can be an alternative to the BGK if the thread starter wants to consider something else.