When to Change Sex
A handy guide from biologists
By Susan Milius
Hollywood does sensationalize, so the unnatural sex-role behavior in last summer’s cartoon hit Finding Nemo shouldn’t have surprised fish biologists. In the movie, a male clownfish loses his mate and most of their offspring in an attack on their home within an anemone, but—here’s the extraordinary part—that older male fish continues to act as a father, and the surviving youngster behaves as a son. To be fair, human children seeing the movie have not seemed greatly traumatized by the anomaly. One can only hope that saltwater aquarium hobbyists keep tanks with juvenile clownfish far from the DVD player.
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While the movie was still in theaters, a study detailing more appropriate behavior for a clownfish appeared in the July 10, 2003 Nature. It reported that clownfish in Papua New Guinea do live as mom-and-dad pairs defending an anemone home. A couple of younger clownfish, often offspring, typically live there too, but they rank lower in the hierarchy, says Peter Buston of the University of California, Santa Barbara. However, his experiments with clownfish clusters in lab tanks showed that when that top female disappears, the surviving fish each put on a growth spurt and rise to the next rung in their hierarchy.