I have a 5 1/2" African Brown Knife. He is special needs though. He came with a fish tank that I bought off of CL and is surely stunted. He had been housed with 3 Red Devils (10", 8", & 7") and a 8" Green Terror for about a year in a 100 gal tank. He now lives in a 125 gal with a Polleni, a Nicaraguanese, a Robertsoni, 2 Sevs, and a Chocolate Pleco. He has his own pvc pipe that he sleeps in. He comes out quite often during the day but is very active at night. He eats earthworm bits from Kensfish.com as well as frozen blood worms (he may eat some of the other stuff I put in for the other fish, but I have seen him eat those).