Meet the Clownfish

Most clownfish species are ideal for aquarists: they are hardy and tolerant of less-than-perfect water conditions, feed readily in captivity, and don’t require a great deal of space. They’re also intelligent and entertaining to watch in a home aquarium.

Clownfish live in the south, central, and western parts of the Pacific and Indian oceans. Some species, such as the Madagascar clownfish, appear in small, discrete areas within this range, while others, like the ocellaris clownfish, exist over a broader geographic range.

Clownfish are also known as anemonefish because of their unusual relationship with sea anemones—invertebrates with tubular bodies and soft tentacles that capture prey like fish and other invertebrates with stinging cells called nematocysts. Clownfish are relatively poor swimmers that are unable to evade most predators when pursued, but unlike other fish, they are immune to the sea anemone’s stinging cells and consequently live, hide, and seek protection in anemone tentacles.

In the wild, a sea anemone serves as the center of a clownfish community. A few weeks after hatching, a young clownfish seeks a home in the tentacles of an anemone. (If a clownfish doesn’t find an anemone, a larger fish will almost certainly eat it.) Once the fish has found an anemone, it’s likely to spend the rest of its life inside and near its new home, rarely straying very far from its shelter.

When a clownfish settles on an anemone that’s already occupied by other clownfish, the new fish assumes the lowest position in the community’s existing social hierarchy. However, if a clownfish settles on an unoccupied anemone, it establishes its own household and grows rapidly into a mature male. When another clownfish of the same species arrives, the dominant male transforms into a female (clownfish are hermaphroditic), the new fish matures into a male, and the two fish mate for life and remain at the top of their community hierarchy until they die.

Although clownfish can’t survive in the wild without the protection offered by sea anemones, pet clownfish can live quite well in an aquarium without an anemone host—and because anemones are especially difficult to care for (and can be dangerous to other types of fish), they aren’t recommended for novice aquarists. Once you have an established aquar­ium, you can add an anemone or a surrogate (anemone-like invertebrate) such as leather and colt corals, elegance coral, or a mushroom anemone, if you choose to do so.

If you plan to include a sea anemone in your clownfish aquarium, research each type carefully to determine its lighting, water-quality, and dietary requirements, and make sure that it’s the appropriate type for the species of clownfish you own. (Each of the clownfish species will only associate with certain anemone species.) Also, purchase a sturdy, healthy specimen—an ailing anemone isn’t likely to recover to full health even with proper care.

There are several different species of clownfish, many of which are commonly available as pets. These species differ in coloration but are fairly similar in terms of size and overall care requirements.

Clownfish of different species that are especially similar are grouped into complexes, of which there are six: the percula, tomato, clarkii, skunk, saddleback, and maroon complexes. (For more information about the different types of clownfish, see Clownfish Varieties.)