September 1, 2008
Clown Fish Sniff Their Way Home
Sniffing its way through a vast ocean to find its home on the coral reef is a real life reality for the tiny, orange clownfish, better known as the fictional character Nemo in the famous Disney cartoon.
That's the finding of a new study led by Australian researchers who used a clever apparatus to measure the fishes' preference for water with 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."
Researchers found 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.
However, the bright, orange fish must search for these anemones. After clownfish eggs hatch near the parents' home anemone, the larvae are carried away by ocean currents.
Researchers wanted to find out how in just eleven days, younger fish settle back into a new anemone, somehow having found their way to their favored abodes.
The study used a chamber with two sources of water flowing side by side. It's important to note the water remains unmixed, with the two types of water flowing parallel to each other.
Researchers introduced clownfish into the chambers and measured how much time they spent on either side.
This process allowed researchers to test the fishes' preference for water from different sources.
Researchers first compared beach water from near vegetated islands with water from reef islands.
"It was ridiculously high how attracted they were to the beach water," said Dixson. The fish spent more than 99 percent of their time on the side of the chamber with beach water flowing by.
"The next step was to figure out what is in the beach water that is making them able to discriminate beach water from the other," she said.
Researchers wondered what cues in the water could draw the fish back to the islands.
"The islands are loaded with trees," Dixson explained, and the water nearby has large numbers of leaves floating on the surface. So, the team exposed ocean water to five different kinds of leaves from the islands, and to a mixture of the leaves, and compared those to ocean water with no leaf exposure. "They were attracted to all of them."
The study found clownfish were not attracted to the tea tree plant, which grows in swamps nowhere near the islands. Scientists determined the fish have specific preferences for the "right" kind of trees.
Research noted that fish bred in aquariums in synthetic seawater were attracted to beach water and to anemone and leaf cues. They surmised this meant the attraction is innate in this species.
"The results are just spectacular," said Jelle Atema of Boston University who developed the testing chamber for his own research and shared one with the Jones group.
"As humans we don't take very seriously the notion of odor in water. It's very foreign to people: How can you smell in water?"
Scientists believe the research has a broad message.
"It shows that there is a connection between the marine and the terrestrial environment," Dixson said. "It shows that the two can't be treated separately, especially in terms of management."
"If you're trying to protect the reef, but you're not protecting the shoreline that calls these 'Nemos' home, it's not going to work," she said.
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