Silvery fish skin as an example of a chaotic reflector

The silvery reflectance in fish skin is studied using an idealized model of the two op­tical components, guanine and cytoplasm. A structure in which the thickness of both components are randomized over an interval gives a calculated reflectance in good agreement with the measured reflectance of two species in the family Trichiuridae, including the behaviour in the infrared. Existing ideas based on quarter-wave stacks, either tuned to different wavelengths or with a progression of optical thickness with depth, have been shown to be unsatisfactory. The random or ‘chaotic’ structure is confirmed by electron microscopy of cross sections of fish skin. The random structure is an example of the phenomenon of optical localization in a biological system.