Popularized by the movie "Finding Nemo," clownfish in the wild live most of their lives in partnership with anemones. Immune to anemones' stings, clownfish lure other species of fish to become the anemones' lunch, cleaning up the leftovers. Specialized body parts -- such as skin, reproductive organs and sensory organs -- not only help clownfish thrive, but make them fascinating aquarium pets.
A Thick Skin
A clownfish's thick skin has pored scales and clear mucus designed to protect him from anemone stings. The tentative relationship begins with the clownfish lightly touching the anemone with his spined dorsal fin and other parts of his body as he swims in a dancing fashion. A clownfish and an anemone become used to one another; you'll see your clownfish snuggle deep within the anemone's tentacles. The relationship depends on the fish maintaining a proper balance of mucus on his skin. If he loses it, too many anemone stings could cause his death.
Going Through the Change
Clownfish all begin life as males, so don't worry about gender when adding a group of juvenile fish to your tank. One fish will become larger than the rest, changing to female sex. Once female, the clownfish can't return to being male and will be the sole breeding female of the group. The female will mate only with the largest male in the tank, and he'll guard the eggs until the fry hatch. Should the female die, the largest male evolves into a breeding female, and the next largest fish in the tank becomes the breeding male.
During breeding, the male cleans debris and creates a dished nesting area with his mouth. After spawning, he'll remove any dead eggs with his mouth as well as use his teeth to deter any predators. Clownfish use their mouths to communicate, raising their heads and moving the bones in their mouths, or snapping their jaws shut. The result is a sound of pops and chirps the fish use as warnings, or a creaky-door sound used to attract mates.
If you want to talk to your clownfish, they'll probably hear you. Bones in their ears known as otoliths help them hear frequencies between 75 Hertz and 900 Hz. The human voice falls well within this range, at 125 Hz to 300 Hz. In their natural habitat, the wide range of hearing helps the fish locate prey, avoid predators and find their way home. Clownfish also sense electrical currents and movement along their lateral line, which runs from gills to tail. They can also sense changes in pressure made by sound and movement in air-filled sacs known as swim bladders, which can also produce sound.