Best neighbors under the sea

Education | Ocean Park 20 Apr 2021

No story about the clownfish would be complete without including their neighbor, or rather, their host - sea anemones.

Mostly found in the shallow waters of the Indian Ocean, the Red Sea and the western Pacific, clownfish take residence among anemones in sheltered reefs.

Also referred as anemonefish, they have brightly colored bodies in orange, red and yellow, with vivid black and white stripes.

This cheerful palette resembling a clown's face paint gives the fish their common name and a picture-perfect contrast with anemones swaying in the background.

Yet the story of the clownfish and anemones goes much deeper than an exterior setting. The pretty anemones have a fatal sting that can kill fish for prey - but not the clownfish, which produce mucous around its body to shield itself from the stinging cells of the particular anemone it is nesting with.

Of the 1,000 species of anemone out there, only 10 can play host to clownfish.

Choosing the right host is elevated to a delicate art here. The clownfish performs a dance with the anemone it is considering moving in with, and then gently touches the anemone's tentacles with different parts of its body. In this way, it becomes acclimated to the host anemone and is able to produce the special mucous needed. Once the clownfish has chosen its host, it rarely leaves, except for short trips to hunt floating plankton.

The partnership is truly symbiotic. The clownfish finds protection by living in the anemone. It also feeds on food scraps left by its host. In return, the clownfish offers first-class service: it consumes parasites on its host and chases away animals preying on it. Its bright colors help to attract fish to come close to the anemone and become its prey. They also produce feces to help fertilize the anemone.

Another interesting fact is that all clownfish are born as males. As they become older, they join small groups of clownfish living together in an anemone.

The largest clownfish in the group is the only female. She mates with the largest male in the group to form a breeding pair. Should anything happen to the female, the largest male will change its gender to become the dominant female and carry on the bloodline.

The female can lay thousands of eggs each time, which the breeding male will then fertilize. Most of the hatched larvae are carried away by ocean currents and perish.

Those that survive use chemical signals in the water to detect suitable anemones for their new homes.

These signals also ensure that the clownfish do not come back to their birthplace to avoid inbreeding.

Both clownfish and anemones inhabit coral reefs - a fragile ecosystem now under serious threat globally. Ocean acidification, warmer sea waters and coastal developments add to their peril. Because of their appealing looks, clownfish are a favorite among coral reef fish collectors.

In case you are planning to keep clownfish at your home, please only buy those raised in captivity and not the ones collected from the wild.

Come visit the adorable clownfish in The Grand Aquarium of Ocean Park. See if you could spot them among the colorful sea anemones.

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May 2021

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