What is an Anemonefish?

G. Wiesen

An anemonefish is one of several different species of fish that are noted for their typically bright coloration and other unusual traits. These fish gain their name from the fact that they live within or around sea anemones, which have highly poisonous tendrils they use to paralyze and eat other types of fish. The bright colors and stripes often seen on these fish allow them to hide among the tendrils of an anemone. They form a symbiotic bond with these anemones, living together in small groups within one. Anemonefish are also quite remarkable for the fact that they are all born male, and are able to permanently change to female for mating.

The clownfish is immune to sea anemone poison and feeds on the crumbs of its host anemone's meals.
The clownfish is immune to sea anemone poison and feeds on the crumbs of its host anemone's meals.

Also known as clown fish, an anemonefish is often recognizable due to its bright coloration and stripes. They come in a fairly wide array of colors, but since most belong to the genus Amphiprion, they tend to be bright orange, red, or pink in color. Anemonefish also usually have several vertical bands of white or black on them, which allows them to more easily hide within a host anemone to avoid predators.

Anemonefish take advantage of the anemone's poisonous tentacles.
Anemonefish take advantage of the anemone's poisonous tentacles.

The way in which an anemonefish is able to live within an anemone, without being killed and eaten by the anemone, is still not fully understood, though there are a few theories. One of the prevailing theories has to do with the mucus layer found on the scales of these clown fish. The mucus layer does not have some of the proteins found in the layers of other fish, which may make these clown fish not appear as prey to the tendrils of the anemone. It is also possible that this layer somehow physically protects the fish from the anemone’s toxins as well.

Once an anemonefish establishes an anemone as a home, however, it will form a symbiotic bond with the anemone. The fish will keep the anemone free of parasites and may also scare away other creatures that feed on anemones, while the waste from the clown fish provides additional nutrients for the anemone. On the other hand, the anemone provides protection for the fish, since most predators will not approach the dangerous tendrils of an anemone, and scraps of fish eaten by the anemone can serve as food for the clown fish.

All anemonefish are born male, but have both sets of sexual organs and are therefore hermaphroditic, though their male organs are dominant. They live in small communities with a single female and a breeding male, with several smaller males that do not mate with the female. When the female dies, the breeding male changes to become female, and then one of the smaller males becomes a larger breeding male. Eggs are laid within or near the host anemone and are usually protected by the large male and may be cared for by the female as well.

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