Freshwater fish, amphibians supercharge their infrared vision

ST. LOUIS, Nov. 6 (UPI) -- Researchers have discovered how migrating fish and amphibians successfully adjust their vision as they move from the land or sea to inland freshwater.

Terrestrial and open ocean environs feature a mostly blue-green spectrum. But particles in freshwater habitats filter out the blues and greens, leaving mostly light on the red or infrared end of the spectrum.

Fish that move from sea to stream must adjust. So do amphibians, as they move from the banks to the stream bed. Scientists at the University of Washington, St. Louis have identified the enzyme that allows these fish and amphibians to supercharge their infrared vision.

"For example, when salmon migrate from the ocean to inland streams, they turn on this enzyme, activating a chemical reaction that shifts the visual system, helping the fish peer more deeply into murky water," Joseph Corbo, associate professor of pathology and immunology, explained in a press release.

The enzyme, called Cyp27c1, is linked with vitamin A, the vitamin long known to be vital to human vision. The enzyme converts vitamin A1 to vitamin A2, enabling the eyes of fish and amphibians to better absorb longer wavelength light.

Scientists found the enzyme in the eyes of zebra fish and also in the top half of the eyes of bull frogs. Bull frogs use half their eye for peering down into water and the other half to look up at the sky.

Researchers say their findings could have a unique application in light-based neurological therapies. Optogenetics is burgeoning field in which light is used to manipulate neurons. Right now, only visible light is used. Visible light can only penetrate the upper layers of the brain. The enzyme could be used to make neurons sensitive to infrared light, and allow optogenetic therapies to penetrate deeper into the brain.

Scientists published their new findings in the journal Current Biology.