Changeable coloration of cornea in the fish Hexagrammos octogrammus

ALTHOUGH fish are considered ‘lower’ vertebrates, the visual apparatus of some species has a high degree of adaptability unparallelled in other vertebrates. For example, members of the Hexagrammidae can change their cornea rapidly from colourless in the dark, to deep red in bright light1,2. We have studied this ability in Hexagrammos octogrammus Pallas, a common shallow-water fish of the Japan Sea, and found that it is caused by the effects of illumination on the distribution of coloured cytoplasm in the corneal chromatophores.