finding nemo’s secret

Don’t tell the children, but Nemo may be a potential transsexual. To ensure harmony in its tight-knit fishy community, it appears that the colorful clownfish can adjust its sex, size, and growth rate, Peter Buston reports in the July 10 Nature. (This is in contrast to most other animals living in social groups, who keep the peace by simply adjusting their behavior.) While at Cornell University, Buston studied almost 100 groups of aquarium-dwelling clownfish. Each group is made up of a breeding pair and up to four non-breeders, and its social hierarchy is rigidly defined by size. At the top of the heap is the largest fish, the breeding female. Fish number two is the breeding male, who is second largest. Then the nonbreeders follow, their size determining their rank. Buston found that if the top-ranking female was removed from the tank, the breeding male changes sex and gets bigger to assume the vacancy, the largest nonbreeder becomes a bigger breeding male, and so on down the line, all the fish changing size to assume their new ranks. Buston wrote that he believes the strategy evolved to prevent violent conflict within the group, so that “subordinates do not become a threat to their dominants.”

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 7/15/2003.