Magazine article Science News

Guys Roll Eyes: Fish Show Some Eyeball to Their Rivals

Magazine article Science News

Guys Roll Eyes: Fish Show Some Eyeball to Their Rivals

Article excerpt

Male fish in the Colorado River roll their eyes to flash a novel "Back off, punk" signal at other males, researchers say.

The razorback suckers' gesture--dipping the eyeball to expose its upper third--ranks as the first documented eye roll among territorial signals, says vision specialist Inigo Novales Flamarique of Simon Fraser University in Burnaby, British Columbia. What makes the communication even more unusual, he says, is that it gets much of its punch from ultraviolet (UV) light.

People don't see UV wavelengths, but biologists have in recent years found that certain fish, birds, and other animals do.

Flamarique had puzzled over the UV vision in a razorback relative, a white sucker that spends most of its life in water too deep for the UV wavelengths of sunlight to reach. Then Flamarique got an e-mail from Gordon Mueller of the U.S. Geological Survey in Denver that described another deep-dwelling fish, the razorback sucker (Xyrauchen texanus), that swims to the shallows to breed. Mueller had noticed bright flashes from the eyes of males staking out breeding territories.

Flamarique says, "All of a sudden, I connected the dots" He hypothesized that those flashes included a UV signal that fish detected in shallow waters.

In lab tests, Flamarique and his colleagues confirmed that razorbacks have UV receptors. They're located where the retina receives light from below and would pick up a signal as one fish swam above another.

During razorback's breeding season, the researchers visited one of the few remaining populations in the Colorado River in Arizona. …

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