The Structural Basis for Iridescent Colour Changes in Dermal and Corneal Iridophores In Fish

ABSTRACT The reflectance from the iridophores in the skin of the neon tetra Paracheirodon innesi (Myers) and the iridophores in the cornea of the sand goby Pomatoschistus minutus (Pallas) changes in response to light. In both cases the reflectance comes from the constructive interference of alternating plates of material of high and low refractive index. In the neon tetra the high refractive index plates are mainly guanine, and the low refractive index plates are cytoplasm. In the goby cornea the plates are made of intercellular matrix and cytoplasm, but it is not known which has the higher refractive index. In neon tetra dermal iridophores, the response to light is a shift to longer wavelength reflection without an accompanying increase in the amplitude of reflectance. In goby cornea, light can induce an increase in the amplitude of reflectance without a shift in wavelength. It is suggested that the wavelength shift is produced by an inflow of material into the iridophore and that the change in amplitude, without a shift in wavelength, is produced by a transfer of material, such as water, between the high and low refractive index layers of the multilayer stack.