I have one right now in a 120 gallon with 2 clown loaches and 2 red-tailed botia, he is about 6" and currently only bothers a rainbow shark. When I first added him he chased everything, now he has a hard time eating since the others destroy the food before he can get to it. Some past experiences with black sharks, do not put any slow moving fish or amphibians with it, they have a tendency of eating on other animals that wont get away fast enough, ex. rope fish, polypterus, gars, paddletail newt, notice that these animals wont fight back either.