Depends on the temperment of the wolf, who came first, and obviously size. when i first got my wolf at 4 inches i added him to a tank with 2 2" convicts a 2.5" firemouth and a 3.5" jack dempsey. all was well he took a few days to establish a territory and then he tolorated everybody else. i then moved the cichilids to another tank and added a 6.5" Ghost Knife. still no problems. tank i moved the cichilids to sprung a leak had to move them back with the wolf (who had the tank mostly to himself for 2 months) he then TERRORIZED them relentlessly at the time he was 5.5" so needless to say a Dominant wolf with Territory doesnt like change. but later i "gradually added" a 3.5" peru wolf i used a tank divider whenever i was away for about a week. and he doesnt mind the second wolf. but no matter what cover seems to be a must with wolves.