Open-ocean fish have silvery scales for skin that re-flect light from above such that the reflected intensity is similar to the background intensity, rendering a fish invisible when looking up, as a predator would; except, many fish can detect polarization – the directional vibra-tion of light waves.
If fish scales acted as simple mirrors, they would im-part a polarization signature to the reflected light much different from the more random polarization of the back-ground light field. This signature would be apparent to a predator able to discriminate polarization. But fish scales scatter polarization, making the camouflage complete. Hence, fish scales render predation a more demanding task. Camouflage via properly polarized fish scales is an amazing evolutionary feat of molecular fine-tuning.