Clownfish (also called Anemonefish)


Photo (taken 3/29/99) shows female captive-bred Solomon Island black percula clownfish (Amphiprion percula) together with a host anemone (Macrodactyla doreensis) in our seagrass aquarium (her smaller mate can be seen in the distance near top-right of photo). In nature, this anemone species naturally hosts clownfish, but not this species of clownfish (Photos of this clownfish pair with eggs, August 2000)

About clownfish


Clownfish are members of the same family as the damselfish (family Pomacentridae, which includes green chromis and many other species), but are distinguished from the damselfish by the tight, lifelong associations they form with various species of anemones (one species of damselfish also associates with anemones, but only when young). Though the various species of damselfish are found in coral reefs and some other habitats around the globe, clownfish occur only in the tropical Western, Central, and South Pacific, the Indian Ocean, and the Red Sea.
Most clownfish species are brightly colored, generally with bold patterns including various combinations of orange, red, yellow, black, brown, or white (and in a few species pale blue), depending on species. The function of this conspicuous coloration is not known for certain, but one hypothesis is that it serves as a warning to potential predators that "if you try to catch me, you'll end up with your face in a mass of stinging anemone tentacles!" Though the fish themselves are not toxic, this could be viewed as a variation on the widespread strategy of aposematic coloration (warning coloration) used by many brightly-colored organisms that are toxic or otherwise noxious, including monarch butterflies, coral snakes, toxic nudibranchs (sea slugs), toxic sponges, and countless others.

Clownfish - anemone mutualisms:


Anemones have stinging cells in their tentacles that are avoided by most fish, but clownfish develop a protective body mucus that allows them to swim among the tentacles without being stung. Clownfish derive protection from predators from this association. In turn, the clownfish protect their host anemone from butterfly fish and other predators that eat anemones, and they keep the anemone free of dirt and debris. Clownfish with a host anemone spend most of their time in contact with or in close proximity to the anemone, making short forays away from the anemone to snatch passing plankton, but retreating to the safety of the tentacles at the first sign of danger. They even sleep nestled in their anemone, and they lay their eggs on a rock surface at the base of their host anemone. Though it is dangerous to assign human emotions to non-humans, a clownfish wallowing among the tentacles of its host anemone looks contented indeed!

In nature, the 28 species of clownfish associate with only10 species of anemones out of the 1000 or so known species of true anemones (true anemones being members of the Anthozoan Order Actinaria. See Overview of Cnidarian Diversity). In the wild, some species of clownfish associate with just one anemone species, others associate with several, and one clownfish species naturally associates with any of the 10 host anemone species. In captivity, clownfish, depending on the species, will sometimes form associations with host anemones they would not normally be found with in nature, or even with anemones that don't naturally serve as hosts for any clownfish species (including Condylactis anemones from the Caribbean).

Though clownfish are always found with host anemones in the wild, they do perfectly well in captivity without them. In clownfish, the instinctual urge to associate with an anemone is strong, however, and sometimes captive clownfish lacking an anemone will adopt other sessile invertebrates as surrogate hosts. Our pair of percula clowns, for example, currently lives in our reef tank where it lacks an anemone host. This pair spends nearly all of its time among the long polyps of a large Xenia elongata soft coral colony on the right side of the reef tank, and every few weeks they lay a clutch of eggs on the rocks near the bases of the Xenia stalks.


Sex change in clownfish


In addition to the mutualistic relationship between clownfish and anemones described above, clownfish are also interesting in that they change sex as they mature. Normally, all clownfish start out as males and only change into females when they reach larger sizes. In the wild, a host anemone will typically be occupied by a large female, a smaller male, and one or more genderless juveniles. A pecking order is established in which the female is dominant, the male is subordinate to the female, and the juveniles are subordinate to the male and to larger juveniles. The male and female form a monogamous pair bond that lasts until one member of the pair dies. If the female dies first, the male rapidly changes into a female, and the largest, most dominant juvenile becomes a male that pairs up with the newly transformed female. (also see: The strange sex lives of reef fishes)


Host anemones in captivity

Most of the ten different clownfish-hosting anemone species are very difficult to maintain long-term in captivity (much more difficult than most species of stony corals). Though some aquarists have had long-term success with a variety of host anemone species, the majority of clownfish hosting anemones in captivity die within a year or so. Indeed, even though the purple Macrodactyla doreensis anemone pictured here is one of the hardier species, we failed with this anemone (for undetermined reasons) after having it for just over a year. This is a shame, since barring accidents, other disasters, or predation, most anemones are essentially immortal; though not all anemones in the wild live to old ages, the ages of individuals of some species in the wild have been estimated at hundreds of years. Clearly, most clownfish-hosting anemones are better left in the wild. Though some species (such as Macrodactyla doreensis) are reported to be quite abundant in the regions where they occur in the wild (and according to some sources not currently in danger of depletion by collectors for the aquarium trade), we should be concerned about overcollection and depletion of wild host anemones in general, for wild clownfish are completely dependent upon their host anemones for protection from predators.

One host anemone species (the bubble-tip anemone, Entacmea quadricolor) has a better track record in captivity, often even reproducing through division in home reef aquaria. This anemone apparently is also abundant over a wide geographic range in the wild and is accepted by many clownfish species. For all of these reasons, this species is considered by many experts to be the best host anemone species to keep in captivity.

Though the idea of setting up a clownfish-anemone mutualism is very appealing to many marine aquarists, beginners should refrain from purchasing host anemones until they are skilled with the maintenance of reef tanks with live corals, and even then, only the hardier species of host anemones should be chosen. Unlike the anemones, however, clownfish are very hardy, typically living and even spawning for many years in captivity (and remember: clownfish do NOT require host anemones in captivity, though various hardy soft corals or long-tentacled stony corals can sometimes serve as surrogates).


Captive-bred Clownfish

Clownfish were among the first reef fish species bred successfully in captivity, and most clownfish species are now commercially available as captive-bred fish. For most clownfish species, there is now no good reason to buy fish captured from the wild. Captive-bred clownfish are generally hardier, more disease free, and in general better adjusted to life in aquaria than are their wild-collected cousins, and when fed properly they are just as colorful. Also, the buying of captive-bred rather than wild-collected clownfish prevents wild host anemones from having their clownfish removed from them (remember that the host anemones depend on their clownfish symbionts for protection from anemone predators). Furthermore, buying captive-bred clownfish supports the breeders who are tackling the often formidable challenges of developing captive-propagation techniques for a variety of other ornamental marine fish species as well.


A wonderful book describing all of the above (and much more) is:
Clownfishes: A Guide to Their Captive Care, Breeding, and Natural History, by Joyce D. Wilkerson. Microcosm Ltd. Shelburne, VT. USA. 1998.
Also see: