A "supercharged" ability to see infrared light helps freshwater fish and amphibians switch between navigating terrestrial and marine environments.

Salmon migrate from the open ocean to murky streams to spawn, and for almost a century scientists have been wondering how these types of fish and some amphibians can shift their vision to see in varied environments, Washington University School of Medicine reported. New research suggests they accomplish the feat by boosting their ability to see infrared light, an ability that humans have never evolved. In open waters the light is blue-green, but when mud blocks the Sun out the light environment shifts to the red and infrared end of the spectrum.

"We've discovered an enzyme that switches the visual systems of some fish and amphibians and supercharges their ability to see infrared light," said senior author Joseph Corbo, associate professor of pathology and immunology. "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."
The incredible enzyme called Cyp27c1 is closely linked to vitamin A, a vitamin known to enhance vision. The enzyme works by converting vitamin A1 to vitamin A2, which can increase the animal's ability to see longer wavelengths.

The new findings could have valuable applications in biomedical research and optogenetics. Scientists could use the newly-discovered enzyme to activate photosensitive neurons with infrared light.

"Just as the enzyme helps fish peer into murky water, it could help us peer deeper into the brain," Corbo said.

The findings were published in a recent edition of the journal Current Biology.