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Ecology and life history

        Clownfish are native to wide ranges of the warm waters of the Indian and Pacific oceans, including the Great Barrier Reef and the Red Sea. While most species have restricted distributions, others are widespread. They are generally highly host specific, and esecially the genera Heteractis and Stichodactyla, and the species Entacmaea quadricolor are frequent partners. The clownfish feeds on undigested matter which otherwise potentially could harm the sea anemone, and the faecal matter from the clownfish provides nutrient to the sea anemone. It has also been suggested that the activity of the clownfish results in greater water circulation around the sea anemone. In addition to providing food for the clownfish, the sea anemone also provides safety due to its poison.

        Clownfish and certain damselfish are the only species of fishes that can avoid the potent poison of a sea anemone. There are several theories about how this is accomplished:

• The mucous coating of the fish may be based on sugars rather than proteins. This would mean that anemones fail to recognize the fish as a potential food source and do not fire their nematocysts, or sting organelles.

• The co-evolution of certain species of clownfish with specific anemone host species and may have acquired an immunity to the nematocysts and toxins of their host anemone. Experimentation has shown that Amphiprion percula may develop resistance to the toxin from Heteractis magnifica, but it is not totally protected, since it was shown experimentally to die when its skin, devoid of mucus, was exposed to the nematocysts of its host.