Hoping to fill your tank with a small school of chromis, cardinalfish, or damsels? Well, good luck, because chances are that it won’t pan out like you had hoped. In nature, fish shoal together in small groups around prominent structures on the reef in order to avoid predation and participate in some sort of social structure (e.g. harems). In the aquarium, these fish will huddle together for the most part, but due to limited space and the absence of several other key factors, these groups quickly dwindle down to a lone individual. More often than not, the fish are picked off one by one by the more dominant or aggressive members, and if the bullying doesn’t get them, stresses from shipping probably will.
In order to actually create a thriving community, we’re told that the key factors are large, well-fed aquariums and groups with massive numbers of fish. Groups of five or six fish don’t seem to cut it, but larger groups seem to do far better. The reasons could be assumed on any number of levels, but the moral of the story is to either avoid creating small schools of fish because they just don’t stay that way long-term.