PARIS: Silvery fish have found a smart way to get around the laws of physics so that they maintain their reflective camouflage in open water, biologists reported on Sunday.
Sprats, sardines and herrings have a skin that neutralizes the polarization of light, enabling them to keep their protective silver cloak, they found. Polarisation describes how light waves travel. Light that is reflected becomes horizontally polarized, meaning that the waves are all oscillating horizontally.
Under a law called the “Brewster window effect,” polarisation leads to a drop in the amount of light that is reflected. This in theory should pose a problem for shoal fish which swim in the mid-water zone, where they have to reflect light from the sky so that they meld into the background and thwart predators.
Reporting in the journal Nature Photonics, British researchers found that underneath the scales of these fish lies a remarkable layer of skin called the stratum argenteum. It comprises alternating layers of proteins, one called guanine crystals that highly refract light, and another, called a cytoplasm, which has a low index for refracting light.
