Some species of fish have a neat trick: They can seem to disappear, leaving predators thinking, "Whuzzuh?? Where'd my next meal go?" How they do this has been a bit of a mystery, but now scientists think they know the answer.
Researchers from The University of Texas at Austin suggest, in a new study just published in the journal Science, that the disappearing act is the work of microscopic structures in fish skin cells called platelets, which reflect polarized light to make the crafty swimmers look, well, "not there."
Polarized light -- light waves all moving in the same plane, like sunlight glare bouncing off water -- typically permeates the scenery underwater, and many fish are able to detect variations in it, using a heightened perception of contrast to help them spot prey.
"Fish have evolved the means to detect polarized light," said Molly Cummings, professor of integrative biology at UT Austin, in a statement. "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."
Cummings and her team studied five species of fish, using special video equipment in an open ocean setting to record each fish's efficacy at hiding itself in the ocean light.
Two fish -- a lookout and a bigeye scad -- were especially adept at camouflage, saving their best hiding skills for when they were viewed from key predator "chase angles": vectors going out in 45 degrees, in all directions, from the fish's head or tail.
Then came the "how." What allowed their skilled deception to take place? Lab study of the disappearing fish revealed platelets in their skin cells that scattered polarized light to varying degrees, depending on the angle.
The researchers' next line of inquiry will be to see if the fish are able to actively use the ability -- perhaps by adjusting the platelets on the fly (or the swim) or by changing to the "correct" swimming angle for hiding whenever predators lurk.
The findings may one day have applications for the military. The U.S. Navy, for obvious reasons, has long been on the lookout for ways to hide in open water, and it was among the supporters of the research.
"I think it's a great example of how human applications can take advantage of evolutionary solutions and the value of evolutionary biology," said Cummings. "It's important for people to recognize that we take advantage of evolutionary processes and solutions all the time and that even our military does."