Aggression is relative. It depends on what you are trying to keep the fish with, and the dimensions of the aquarium. Do you wish to keep a group of demasoni, or a single one in a mixed Malawi tank?
In groups, it is recommended to keep at least 12 to start, preferrably more, as they are quite aggressive towards each other. Typically, they aren't that bad to other non demasoni species, though there are exceptions.