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Clown Fish

 

Clownfish and Damselfish are the only species which can avoid the stings of an anemone, which can be quite potent. The exact mechanism by which this is accomplished is the subject of debate, and there are several theories which may all be partly responsible. The details of these theories are complex, but they fall into two major categories.

One theory is that their slime coating is based on sugar rather than proteins so anemones fail to recognize the fish as food and do not fire their nematocysts, or sting organelles. A similar theory is that the mucous coating mimicks the anemone's own coating, a theory that is bolstered by the fact that it takes several days for a Clownfish to adapt to a new species of anemone. There is no acclimation period when a Clownfish is moved to another anemone of the same species. It is interesting to note that not all anemones make suitable hosts--many can and will sting and eat Clownfish. Also, particular species of clownfish will only use particular species of host anemones in nature. In captivity, certain Clownfish species will adapt to certain other anemone species, but not many. Another likely possibility is that their unique movements, which are unlike any other fish, let the anemone know that they are not food. This theory is bolstered by the fact that juvenile Clownfish, which have no coating, will immediately seek refuge in any compatible anemone and will not be stung. Juvenile clownfish will not survive for long without the protection of an anemone, and few actually find one before being eaten.

Clownfish live in small groups inhabiting a single anemone. The group consists of a breeding pair, which cohabit with a few non-reproductive, "pre-pubescent", and smaller male clownfish. When the female dies, the dominant male changes sex and becomes the female. This life history strategy is known as sequential hermaphroditism. Because clownfish are all born as males, they are protandrous hermaphrodites (pro=first; androus=male)  This is in contrast with another form of hermaphroditism, known as protogyny, in which all fish are born as females but can change to males later. Clownfish lay eggs on any flat surface close to their host anemones. In the wild, clownfish spawn around the time of the full moon and the male parent guards them until they hatch about 6 to 10 days later, typically 2 hours after dusk.

Clownfish are omnivorous: in the wild they eat live food such as algae, plankton, molluscs, and crustacea; in captivity they can survive on live food, fish flakes, and fish pellets. They feed mostly on copepods and mysids, and undigested food from their host anemones.  Depending on the species, clownfish can lay hundreds or thousands of eggs. Clownfish were the first type of marine ornamental fish to be successfully bred in captivity on a large scale. It is one of a handful of marine ornamentals whose complete life cycle has been successfully completed in captivity.