Air Date: Week of July 25, 2003

Living on Earth’s Cynthia Graber reports on a new discovery about why clownfish sometimes change their size and sex.

Transcript

ROSS: Coming up: a journey to the bottom of the Black Sea. First, this Note on Emerging Science from Cynthia Graber.

[EMERGING SCIENCE NOTE THEME]

GRABER: If the animated film character Nemo were a real fish, he might not stay a boy forever. That’s because Nemo is a clownfish, and clownfish can change sex at different points in their lives. Scientists have been on to this phenomenon for years. They also knew that clownfish can change size, even after reaching adulthood – but they didn’t know why. Now one scientist says he has an answer.

Peter Buston of Cornell University spent a year in Papua New Guinea, diving four to six hours a day tracking clownfish. Buston noticed that within each group of fish that live together in a sea anemone, there are two breeders, the female being slightly larger than the male. Then there are three or four non-breeding clownfish, each getting progressively smaller down the hierarchical line. Buston discovered that when one of the breeders dies, each fish moves up the ladder. If the female dies, the breeding male grows larger and becomes a breeding female. Then the largest non-breeder morphs into a breeding male.

Buston says the little clownfish stay little because if they grew large, the breeders might see them as a threat and force them out of the protective anemone. So, as far as clownfish go - sometimes it’s better to be a small fish in a big pond.

That’s this week’s Note on Emerging Science, I’m Cynthia Graber.

ROSS: And you're listening to Living on Earth.

[MUSIC: Wes Montgomery “Movin’ Wes’, Pt. 1” Compact JazzPolygram (1987)]