The Skeptical Aquarist

The prime positive criteria in setting up a genuine community aquarium all tend to resolve into questions of ecological niches. Appropriate tankmates won't be in direct competition. Good planning before you even begin to lay gravel into a new tank can increase the number of territorial niches made available in it, and they will increase your opportunities for keeping more species of fishes healthy and content enough to be displaying at least some aspects of their natural behavior. Besides the territory they inhabit, some other niches help define a fishes' relation to its ecosystem. What are the criteria for territorial and other niches that would shape a genuine, thriving fish community, within the aquarium's miniature, and simplified habitat?

Living space. As I mentioned, one clear series of niches is defined by the physical spaces you can arrange in your aquarium. Topdwellers, open midwater shoaling swimmers, temporary station keepers or more permanent territory holders--— both the shy lurkers and the lurk-and-pounce carnivores--— bottom-dwellers, root- and cave-dwellers: each life-style has specific requirements for the aquarium's spaces. Some combinations of species will keep so consistently to their stations that they scarcely interact with one another. Merely adding a few floating plants to an aquarium can provide a new living space for surface-dwellers that need a sense of security.

Nutrition. Another clear series of niches is defined by what these fishes need to eat. Carnivore, omnivore, herbivore, detritivore ("scavenger") are familiar feeding categories, but fishes are adaptible opportunists. Modern teleost fishes have been so successful partly because they are able to divide up resources among them and specialize. There's usually some overlap in feeding categories: the algae-eater working over the green film is ingesting many minute animals, while the carnivore eating that frozen brine shrimp is improvising this time as a detritivore.

Time-based niches. When they are living free in their natural habitats, fish species further divide up their living space according the times of day they are active. An old English music-hall comedy routine called "Cox and Box" involved a boardinghouse landlady who rented the same room twice over, to Cox, who worked all day, and to Box, who worked all night. Fishes may be diurnal like Cox, or nocturnal like Box--— or they may be "crespuscular," doing most of their foraging and feeding in the half-light of twilight and pre-dawn. What efficiently divides up the territory in nature often turns into a "Cox-and-Box routine" in the narrow confines of a tank, and daytime fishes may be terminally stressed by sharing a tight space with an inquisitive or aggressive nocturnal catfish, such as some Synodontis species.

Social niches. Shoals and schools, jealous loners, pecking orders: there are many ways fishes define their social space. In all but the very largest tank, one school of fish will constantly break up the schooling patterns of a second school. "One school to an aquarium" is a good rule-of-thumb.

Thinking in terms of niches. So, instead of the aquarium communities that aren't much more than ordinary menageries and cockpits, what if you were to think of an aquarium as a microcosm of a natural community? A microcosm that functions as a representation of some simplified part of an ecological "community." If a genuine community is something you're striving for, I think you'll get more satisfaction if you think in terms of niches. In terms of niches, you can put together a perfectly authentic community of fishes, even though the actual species you combine come from similar waters in widely separated parts of the world, if you'll begin with one species of fish and build a niche-defined community around that species. That would create an extended "Species Aquarium"

Or you can take the extra step of limiting your species to a very narrowly defined part of the world, an ecotope. The result would be an "Ecotope Aquarium."

The next two pages expand on these two kinds of communities.