The Skeptical Aquarist

Alternately, begin with a specific environment. The other way to organize your community is as an "ecotope," in which you recreate a very specific environment and populate it with two or three compatible species that characterize that environment.

Why do I want to call these "ecotopes" rather than "biotopes"?

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.

Our usual mixed community aquarium isn't really much more than a menagerie, a random assemblage of fishes. The first signs that you're moving beyond the "box of fishes on dialysis" phase of "fish-only" fishkeeping are some new questions that start to occur about keeping one species of fish with another, about special requirements fish may have, beyond their temperature ranges and pH preferences. Soon you begin to feel that concerns like "Will my angels eat my neons?" (answer: "Not this week") are resulting in a menagerie rather than a community.