Clownfish and Sea Anemone Behavior

Probably the most famous example of a symbiotic (“living together”) relationship on the coral reef — if not in the entire animal kingdom — is the remarkable relationship between clownfish and anemones.

How important is this relationship to the partner organisms?

It seems that both organisms benefit considerably from the arrangement, but while only about 1% of all anemones host fish in this way, all species of clownfish in the wild are compelled to seek out an anemone. By living among an anemone's tentacles, the fish gain a protective refuge from predators, which are reluctant to expose themselves to a battery of stinging nematocysts. Clownfish are relatively poor swimmers and without the anemone will become the prey of larger fish sooner or later. The relationship is perhaps less important to the anemones, although some, like the bulb tentacle anemone (Entacmaea quadricolor) cannot live without co-habiting fish in the wild. The clownfish provide protection for their anemones, driving off possible predators, such as butterflyfish.

What other benefits do clownfish provide for their anemones?

Aquarists occasionally report instances where clownfish seem to feed their anemones, but it seems unlikely that this happens in nature, where the diet of clownfish is less likely to consist of large, messy chunks of food that might fall into the anemone's eager tentacles. The fish may, however, benefit their host by fanning them with water and keeping them free of parasites.

Can all clownfishes live with all anemones?

There are approximately 27 species of clownfish, but not all of these are able to live with the 11 anemones (out of around 1,000 species worldwide) that host fish. In fact, only the yellowtail clownfish (Amphiprion clarkii) is thought to occur naturally with all host anemones, while some clownfish are only found in the wild with one anemone species. There are even a few other species of fish and inverts that live with anemones to a greater or lesser extent, including the blunt-headed wrasse (Thalassoma amblycephalum) and the porcelain anemone crab (Neopetrolisthes ohshimai).

How are clownfish protected from the stinging cells of their host anemones?

Clownfish are protected from the stinging cells of their host anemone by a coating of protective mucus over their bodies. The fish are actually vulnerable to the anemone's toxins, but the mucus prevents the stinging cells from firing. However, whereas the yellowtail clownfish seems to have developed more or less permanent, general protection, most clownfish species have to acclimatize to a new anemone.

During this process, the fish start off by touching their ventral fins and belly area to the stinging tentacles of the anemone — and are stung in the process. Over a period of several hours, the fish become immune to the stings and can venture deeper into the anemone. Whether the protective mucus is produced by the fish itself, or is gathered from the anemone, or both, is unclear, but it works by preventing the anemone from recognizing the fish as a threat. In effect, the fish chemically mimics the anemone – and thus stops the stinging nematocysts from firing.

How do clownfish choose their anemones?

Al If a fish chooses the wrong species of anemone when it settles, it could easily be killed. Juvenile clownfish are able to locate their anemones using chemical recognition of particular host species. Clownfish eggs are laid in close proximity to their host anemone and it seems likely that during this developmental stage, the embryonic fish may be imprinted with chemical cues from the anemone.Thus, when they select an anemone in later life, they choose the same species that their parents occupied.

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