I have one red tailed black shark, along with two rainbow sharks, and a blue botia (which has a similar temperament). They're in with much smaller tiger barbs and get along fine. They are territorial and I have plenty of caves and nooks for them to stake out... The sharks only chase each other out of their defined territory and leave everyone else alone. In my opinion, get one shark or more than four or five. They're beautiful, active, and fun to watch