Damselfish and Clownfish (Family Pomacentridae)
Individuals of the more than 325 species that comprise this large family of fish are among the most numerous and conspicuous fish on many coral reefs. Members of this family are found throughout the world's tropical and semitropical seas, with the greatest diversity occurring in Australian waters and the lowest in the Atlantic and East Pacific oceans. They occupy a startling variety of habitats, with many species restricted to specific depths or specific areas of wave action.
Anemone fish, or clownfish, are well-known for living in close association with marine invertebrates known as sea anemones (see color insert for photo). Usually home to just one pair of clownfish, the host anemone forms the basis of their territory, and they rarely stray far from it. Long thought to be immune to the anemone's stinging tentacles, the clownfish is now known to secrete mucus that mimics that covering the tentacles of the anemone. This mucus inhibits the tentacles from stinging one another and, in essence, prevents the anemone from recognizing the clownfish as prey. The clownfish thus derives protection from the anemone and returns the favor by chasing off fish that might prey on its host.
Why do many species of damselfish so zealously guard their territory?
One explanation is that they are protecting their food source, algae. The thick mats of this favorite food often grow within well-guarded territories but they are absent outside these territories due to a large number of other animals that eat algae.
Damselfish are generally small, brilliantly colored, and in almost constant motion. These characteristics render them quite popular with aquarists. The speed at which they move and their eagerness to feed allows them to survive in aquariums with much larger fish. Be aware, however, that they can be quite aggressive toward their own and similar species.
A true darling of the aquarium world, the percula is one of the most widely recognized marine fish in the world. Its brilliant coloration and “comic” mode of swimming endears it to all. Hailing from the Indo-Pacific region, this clown-fish reaches a length of 3.2 inches. The percula is quite protective of the anemone in which it lives, and generally only one pair per tank can be maintained. It accepts a wide variety of dried and frozen foods. If you are considering a percula clownfish, be sure to select a captive-bred animal, which is readily available. Also, remember that they are best displayed with a living anemone, and that the keeping of anemones is a separate discipline. Carefully read the section on anemones in Chapter 10 before deciding to purchase one.
The relationship between the clownfish and their hosts might best be described as “commensal,” in that they seem to derive benefit from living in close association with each other, but are not strictly limited to that situation. The vast majority of anemones live without clownfish. Clownfish, however, seem more dependent upon the relationship. While they will live well alone in the aquarium, experiments in the wild have shown that clownfish without anemone hosts are quickly eaten by larger fish.