Anemonefish, also called clownfish, live nestled among the tentacles of stinging anemones. Scientists have found that these fish have a special layer of mucus that keeps the anemones from stinging them.
Anemonefishes need the protection they find in their anemones: the anemones' stings keep fish predators at bay, and an anemonefish never lives without its host anemone. The partnership may benefit the anemones, as well. They get scraps of food dropped by the anemonefishes as they eat. And the aggressive and territorial anemonefishes may defend their anemones by driving away butterflyfishes and other anemone-eating fishes.
In places, unscrupulous collectors use cyanide, bleach and other chemicals to catch coral reef fishes for the pet trade. Applying the chemicals stuns the fishes and makes them easy to collect. But these poisons can also kill fishes, corals and other reef life. If you have a home aquarium, buy fishes raised in captivity, not ones collected from the wild.
All anemonefishes start life as males. As they grow, a male may change to become a female.
Before a clownfish can call an anemone home, it has to get comfortable. The fish gently touches the anemone's tentacles over a period of several hours or days, until the fish forms a layer of mucus that's resistant to the stings.
Living with a fish in your tentacles has its good points. Clownfish are very protective of their anemone homes, and chase away other fish, and even divers. Anemones also get food out of the deal—scraps that are dropped by the clownfish—as well as fish poop.