Silvery Fish Elude Predators With Sleight of Reflection Jeffrey L. Rotman/Getty Images Silver fishes' skin reflects light at multiple layers without polarization. Silvery fish like sardines and Atlantic herring are masters of camouflage. A new study explains how the fish use their silvery skin to stay invisible to predators from nearly every angle. "What these fish do is get around a fundamental law of reflection," said Nicholas Roberts, a biologist at the University of Bristol and one of the study's authors. Typically, when light is reflected from different surfaces, any light that comes off the path of that reflection becomes polarized. That's why fishermen wear polarized sunglasses. Silver fish avoid this problem because of the unique makeup of their skin, which has alternating layers of cytoplasm, as well as two types of guanine crystals (which refract light). The two types of crystals have different refractive indexes that create a unique reflective property. "The polarization happens over a range of angles instead of one, and the end product of having all the layers together is that it creates a polarization-neutral reflector," Dr. Roberts said. Over time, the fish have evolved to have the perfect ratio of the two types of guanine, and as a result have a near-constant reflectivity, providing them an invisibility cloak from all angles, Dr. Roberts said. The mechanism is common to all silvery fish, he said. He and his colleagues report their findings in the current issue of the journal Nature Photonics. A report in the Observatory column on Tuesday about the light-bending properties of the skin of silvery fish misidentified the item that fishermen wear to offset the polarization of light coming off the water. They wear polarized sunglasses, not polarized vests.