Secret to Fish's Waterfall-Climbing Ability Found

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Wailua Falls, island of Kauai, Hawaii Photo by Alejandro Bárcenas (Wikimedia Commons)

Content provided by Charles Choi, LiveScience

A waterfall-climbing fish in Hawaii uses the same muscles to both rise and feed, researchers have discovered.

Scientists looked at the Nopoli rock-climbing goby (Sicyopterus stimpsoni), also known in Hawaiian as o'opu nopili.

This plant-eating fish is found throughout Hawaii, and was once greatly

relished as food, apparently being a favorite snack among priests.

Many gobies

can inch their way up waterfalls with the aid of a sucker on their

bellies formed from fused pelvic fins. The Nopoli rock-climbing goby, on

the other hand, can climb waterfalls as tall as 330 feet

(100 meters) with the aid of a second mouth sucker, which develops

after their mouthparts move from a forward-facing position to under the

body during a two-day-long metamorphosis into adulthood.

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"For a human to go the equivalent distance based on body size, it'd be

like doing a marathon, some 26 miles (42 kilometers) long, except

climbing up a vertical cliff-face against rushing water," researcher

Richard Blob, an evolutionary biomechanist at Clemson University in

South Carolina, told LiveScience. Indeed, an old Hawaiian saying is that

as the Nopili clings, so will luck.

The goby, which can grow up to 7 inches (18 centimeters) long as an

adult, feeds by cyclically sticking the tip of its upper jaw against

rock to scrape food off surfaces. This behavior is quite distinct from

other Hawaiian gobies, which feed by sucking in food from the water. Given the apparent similarity of the climbing and feeding behaviors of the S. stimpsoni species, researchers thought one might have developed from the other. (See Video of Waterfall-Climbing Fish)

"The fish gave us an opportunity to see how unusual behaviors evolved," Blob said.

To see if these behaviors really were as similar as they looked, the

scientists captured Nopoli rock-climbing gobies from a stream on the

island of Hawaii by net while snorkeling and kept them in aquaria. They

next filmed the gobies' jaw-muscle movements as the fish climbed and

ate, either scraping food off glass microscope slides or climbing up

angled plastic boards. They found that overall movements were indeed

similar during both activities.

It remains uncertain whether feeding movements were adapted for climbing, or vice versa.

"To understand the sequence of steps in the evolution of this extreme

behavior, we want to look at closely related species that do one of the

behaviors, but not the other," Blob said. "This fish has relatives in

many oceanic islands, such as the Caribbean."

The scientists detailed their findings online Jan. 4 in the journal PLOS ONE.

They will also present their findings Jan. 6 at the Society for

Integrative and Comparative Biology annual meeting in San Francisco.

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