Easy to Moderate - Dietary needs more specific. Needs a well established aquarium. Requires a small degree of experience in the hobby.

Moderate - Requires a more stable environment. Water quality tolerance is more strict. Dietary needs somewhat specific.

Difficult - Same as 3 above. However, may require more fish keeping experience than 3. Requires an environment similar to their natural habitat.

Very Difficult - Difficult to maintain in captivity. Requires a specific diet such as in nature. Requires a knowledge of natural environmental elements. Strict water quality parameters necessary.

Extremely Difficult- Mostly impossible to maintain in captivity. Most are specialized feeders, e.g. coral polyps, sponges, etc.