more than likely the only fish they will bully will be fish of their same shape or close to it and/or anything that may try to creep into their cave-space. That goes for bala's, rainbow sharks, abino rainbow sharks, probably most other sharks as well as most sport that torpedo shape. Anything else, they tend to leave alone. You might buy 2 and think they are fine and they will be for a little while but as they mature, so does their sense of territoy and with it is their aggression. The more mature, the higher the aggression. The sharks will kill to be the ruler of the floor if left long enolugh so it's advised against more than one.