Scientists have solved a longstanding mystery about how some fish seem to disappear from predators in the open waters of the ocean, a discovery that could help materials scientists and military technologists create more effective methods of ocean camouflage. In a paper published this week in Science, a team led by researchers at The University of Texas at Austin reports that certain fish use microscopic structures called platelets in their skin cells to reflect polarized light, which allows the fish to seemingly disappear from their predators. 

Polarized light is made up of light waves all traveling in the same plane, such as the bright glare you sometimes see when sunlight reflects off the surface of water.

Under the surface of the water, light tends to be polarized. Many fish--and sophisticated modern satellites--have the ability to detect variations in such polarized light.

"Fish have evolved the means to detect polarized light," said Molly Cummings, professor of integrative biology in the College of Natural Sciences. "Given that, we suggested they've probably evolved the means to hide in polarized light. If we can identify that process, then we can improve upon our own camouflage technology for that environment."

Whether it's a predator pursuing a fish or a satellite seeking an adversary, light patterns help with detection of targets in the the open ocean in three ways: through brightness contrast, color contrast and polarization contrast. Of the three, polarization contrast is considered most effective for detection in the open ocean. 

The U.S. Navy has sought for many years to learn how to hide in open water and supported the work of Cummings and her colleagues exploring how fish avoid detection in the open ocean. In a previous study, the researchers demonstrated in the lab that a fish called the lookdown was able to manipulate polarized light to its advantage. The new study--conducted in the actual ocean, not just in test environments--shows lookdowns and other fish that live in the open ocean camouflage themselves this way.