October 23, 2012 — Silvery fish such as herring, sardine and sprat are "breaking" the basic physics law of reflection, according to a study from the University of Bristol published this week in Nature Photonics.
Reflective surfaces polarize light, but PhD student Tom Jordan and his supervisors Professor Julian Partridge and Dr Nicholas Roberts in Bristol's School of Biological Sciences have discovered that these silvery fish have defeated this basic law of reflection, which helps protect them from predators.
Until now, it was believed that the fish's skin, which contains "multilayer" arrangements of reflective guanine crystals, would fully polarize light when reflected, thereby reducing reflectivity and making them more visible to predators.
However, the Bristol researchers found that the skin of sardines and herring contain two types of guanine crystal instead of one – each with different optical properties. As these two types work together, the fish's skin does not polarize the reflected light and keeps its high reflectivity.