Three species of silvery fish seem to have found a way around a law of physics that governs the reflection of light.
The skin of the Atlantic herring (Clupea harengus), European sardine (Sardina pilchardus; pictured) and sprat (Spratus spratus) is made up of alternating layers of cytoplasm and highly reflective crystals of guanine — a molecule that is also found in DNA and RNA. Nicholas Roberts and his colleagues at the University of Bristol, UK, report that the fishes' skin can reflect light without polarizing it, even when the light hits the reflectors at angles that would normally result in fully polarized reflections. The skin contains a mixture of two types of guanine crystal with different optical properties — when the two are present in a specific ratio, this mixture prevents polarization and maintains high reflectivity.
These reflectors help the fish to camouflage themselves by matching the light environment of the open ocean, say the authors. Moreover, the principles at work in these fish could have applications in optical devices such as light-emitting diodes.
Nature Photon. http://dx.doi.org/10.1038/nphoton.2012.260 (2012)
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