Researchers with the University of Texas at Austin have published a paper in Science that says certain fishes use platelets in their skin cells to reflect polarized light, effectively acting as a camouflage that enables the fish to “disappear” in waters in which their predators are lurking or their prey is swimming.
“Fish have evolved the means to detect polarized light,” said Molly Cummings, professor of integrative biology at the university’s 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.”
Previous studies at the university with the lookdown (Selene vomer) fish showed that it had the capability to change how light reflected on it in a lab setting. This study was conducted in part in the ocean and showed that the look down and other fish can camouflage themselves to deter predation.
The researchers used a device called a video polarimeter, which records polarized light in real time. This enabled the researchers to view polarized light as the fish do. They then worked with scientists from other universities to build an automated rotating platform that kept the fish in place while the video polarimeter took measurements. More than 1,500 measurements were taken and combined with data such as angle of the sun and position of the fish, the researchers were able to determine that the look down and the big eye scad had better camouflage in polarized light than a mirror. These two species also blended better than two reef species and surface skimming fish, which live in areas of the ocean where polarized light is not important to their survival. They also determined that the look down and the big eye scad were better hidden in what the scientists called chase angles, or the position the fish take when either being hunted by a predator or chasing prey.
The capability to camouflage themselves in polarized light is due to the structure of platelets in the fishes skin cells. These platelets scatter polarized light depending on the angle of the light coming down on the fish.
The research was funded by the U.S. Navy, the National Science Foundation, and a College of Natural Sciences Catalyst Grant. The researchers will try and determine if the fish can manipulate the capability to camouflage by changing the angle in which they swim or if they can manipulate the platelets in their skin.