Nemo Sniffs His Way Home

Aug. 29, 2008 -- Tiny orange clownfish, made famous by the Disney character Nemo, use the smell of leaves and anemones in the water to find their way home on the coral reef.

That's the finding of a new study using a clever apparatus to measure the fishes' preference for water carrying different odors.

A team led by Geoffrey Jones of James Cook University in Townsville, Australia surveyed waters around Papua New Guinea for clownfish populations.

"The boat captain said, 'If you want to find the orange clownfish, you have to find islands. The fish need to see trees,'" said study lead author Danielle Dixson. The survey confirmed this observation: "There's a huge statistical difference [in the numbers of clownfish] between where there are islands and where there are not islands."

For reasons that are unknown, the two types of anemones that the region's clownfish call home only live near islands with trees and beaches and are not found on "islands" made only of reefs.

But the fish have to search for these anemones, because after eggs hatch near the parents' home anemone, the larvae are carried away by ocean currents. About 11 days later, the juvenile fish settle back into a new anemone, somehow having found their way to their favored abodes.

The researchers set out to figure out how.

They used a chamber with two sources of water flowing side by side. At the top, a wall divides the chamber, separating the water sources. Lower down, the wall disappears, but the water remains unmixed, with the two types of water flowing parallel to each other.

The researchers introduced clownfish into the chambers and measured how much time they spent on either side. This allowed the researchers to test the fishes' preference for water from different sources.

First they compared beach water from near vegetated islands with water from reef islands.