No Nemo: Anemones, Not Parents, Protect Clownfish

By John Roach
for National Geographic News
June 5, 2003

In the hit movie Finding Nemo an overprotective clownfish named Marlin searches for his son Nemo who is swiped from the Great Barrier Reef and plopped into a fish tank at a dentist's office in Sydney, Australia.

The true protectors of clownfish in the ocean, however, are not parents but rather prickly, stinging sea anemones that live on reefs.

"There is no bond between a fish and its parents," said Daphne Fautin, an invertebrate zoologist at the University of Kansas in Lawrence and an expert on the relationship between clownfish and sea anemones.

Clownfish, which are also called anemonefish, are relatively small. The largest of them grow not much longer than 5 inches (13 centimeters) and they are prone to being devoured by any larger fish-eating fish such as grouper, said Fautin.

For protection, clownfish seek refuge amongst the tentacles of sea anemones. The tentacles contain harpoon-like stinging capsules called nematocysts that the anemones employ to capture prey and ward off predators.

In a yet-to-be resolved biological mystery, clownfish have mucus on their skin that somehow protects them against the sting of their host anemone. As a result, the clownfish are able to stick near their host which is avoided by most other fish in the sea.

"The clownfish gets protection by hiding sting-free among the tentacles. If you remove the clownfish, large butterfly fishes will eat the anemone," said John Randall, an ichthyologist at the University of Hawaii at Manoa.

Butterfly fish are predators of the sea anemone. In certain areas of the tropics where clownfish, sea anemone, and butterfly fish exist, clownfish scare off butterflyfish from their host anemone. Research has shown that if the clownfish are removed from the anemone, butterfly fish will move in and devour the anemone. So, the protection of the anemone afforded by the clownfish is part of the mutual relationship.

In addition to scaring off predators, some scientists speculate that clownfish waste may serve as a nutrient for the anemones. In certain cases, however, sea anemones appear to derive no apparent benefit from the clownfish, said Fautin.

Clownfish Hierarchy

There are more than 1,000 species of sea anemones found throughout the world's oceans. Only ten of these species share their niche with clownfish, which thrive in the tropical waters of the Indian and Pacific oceans.

Each individual host anemone is home to one group of clownfish, which contain a dominant breeding pair and up to four smaller, subordinate fish. There are 28 known species of clownfish, so more than one species of clownfish may take to any given species of anemone.

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