Changeable Coloration of the Fish Eyes:
Corneal Spectacles

S.L. Kondrashev, O.Yu. Orlov

Institute of Marine Biology, Russian Academy of Sciences,
Far East Division, 690041 Vladivostok, Russia
Institute for Problems of Information Transmission,
Russian Academy of Sciences, 127994, Moscow, Russia


Yellow or orange coloration of the ocular media in fish has been reported by a great number of investigators. In some species the pattern of this coloration could be rather curious - see fig.1 (20K) and fig.2 (26K). The fish, masked greenling Hexagrammos octogrammus (see left picture), inhabiting boreal West Pacific shallow waters was the first in which the phenomenon of the changeable corneal coloration was discovered and investigated in many details (Orlov and Gamburtzeva, 1976). It was found that corneal coloration change reversibly follows the changes of the ambient illumination: from intensely colored in the bright light to colorless in the dark. The process of full de- and re-coloration lasts appr. 1-1.5 hours.

Since that time, we searched for other fish possessing the same striking characteristic during expeditions in the Sea of Japan, Okhotsk Sea, South China Sea, Black Sea, White Sea and Baikal Lake. Some specimens were collected by US colleagues in Friday Harbour and in freshwater streams in States of Oregon and NY. It was found that greenlings were not the only example and many representatives of the fish class are shown below in the LIST. We put on the list also some species which had been earlier reported to have corneal coloration, but no indication had been given of its changeability (Muntz, 1973; Lythgoe, 1975). We have no reason to doubt its rightfulness since the ability of the corneas to change coloration has been proved significantly for other fish from the same genera and families.


Dark adapted cornea of Hexagrammos octogrammus
Changeable coloration results from the presence in the cornea of specialized chromatophores (corneal staining cells) the bodies of which are localized at the periphery and single processes of the cells reach for the pupil zone. As it is seen from the montage of the cornea images in the dark adaptated state at left, the number of cells in the dorsal part of the cornea is usually greater than in the ventral region. In big eyes and corneas this single cell process can reach up to 1 cm long - see fig.3 (56K). It is interesting to note, that such unusual chromatophores were, obviously, described for the first time in fish, Cottus bairdi, by G.L.Walls, but without touching their sophisticated light-shading functions. This classic of visual science compared the pattern of the “very long heavily pigmented” cell processes with an effect of “yellow waterfall” (Walls, Judd, 1933).

It is the reversible movement of carothenoid pigments in yellow or orange cells from the body to the process that is responsible for recoloring of the cornea when illumination is altered. Hundreds and thousands processes coming from the corneal margins (right picture) make a colored film. In most of species the coloration is uniform, but in one species - Irish lord, Hemilepidotus gilberti (Cottidae) it appears that in the light adapted state all the pigment from the body “leaks” into some lacunes at the tips of the cell processes, thus making a fascinating “patch”-pattern over the whole cornea - see fig.4 (99K), resembling a dotted pattern of a constant corneal coloration in Labrid fishes Crenilabrus sp. from the Black Sea (see fig.1).


The development of corneal staining cells (CSCs) and changeable light filter formed by CSCs was studied in the sculpin Porocottus allisi (Cottidae). First CSCs appear in the dorsal hemicornea when the operculum covers the first gill arch, which we consider a sign of an early stage of larval development (several days after hatching). The development begins with the stage of drop-like chromatophore; on day 1 of development, these 0.018-mm cells are irregularly shaped and are filled with bright orange opaque granules - see fig.5 (28K). Later on, the number of cells increases, first small processes are formed accompanied by granular structure appearance in the cytoplasm - see fig.6 (42K). In subsequent development, the cell becomes rounded and lanceolate forming a single process extended towards the pupillary zone. On day 3 of development, the process is relatively short and wide. Beginning from this moment, the cell responds to illumination changes. The process of light filter formation starts in the dorsonasal cornea expanding dorsally and finishing in the ventral cornea 6 days after the beginning. The development of the whole system of CSCs completes within 9-11 days and coincides with the metamorphosis of larvae (Gnyubkina, Kondrashev, 2001).

of fishes with changeable corneal coloration


We give our sincere thanks to our colleagues, V.P.Gnyubkina, T.N.Manchenko, A.V.Levin, A.S.Sokolovskii, D.L.Pitruk and S.Sh.Dautov (all at the Institute of Marine Biology, Vladivostok) who helped much to catch fish, Prof. Neil Bourne (Nanaimo Bilogical Station, Canada) and Dr. R. Daniels (N.Y. State Education Department, Albany, NY, USA) who helped to get some of the fish specimens, Igor I. Sheremetjev (Kiev, Ukraine) who provided us with a valuable information about tropical aquarium fishes, and also to Dr. V.V.Maximov (IPIT RAS, Moscow) who stimulated us to use the advantages of the Internet.


Appleby S.J., Muntz W.R.A, Occlusable yellow corneas in Tetraodontidae, J.Exp.Biol., 1979, v. 83, pp. 249-259.

Gamburtzeva A.G., Svitkina T.M., Tint I.S., Kondrashev S.L., Sakharov V.B., Pecularities of the chromatophore surface structure in the fish cornea with changeable coloration, Tsitologiya, 1993, v. 35, pp. 49-53 (in Russian).

Gnyubkina V.P., Kondrashev S.L. The development of specialized chromatophores and a changeable light filter in the cornea of the sculpin, Porocottus allisi. Russian Journal of Marine Biology, 2001, v. 27, N 1, pp. 31-35.

Kondrashev S.L., Gamburtzeva A.G., Gnyubkina V.P., Orlov O.Yu., Pham Thi My, Coloration of corneas in fish. A list of species, Vision Res., 1986,v. 26,pp. 287-290.

Lythgoe J.N., The structure and function of iridescent corneas in teleost fishes, Proc. Roy.Soc. London, 1975, B188, pp. 437-457.

Moreland J.D., Lythgoe J.N., Yellow corneas in fishes, Vision Res., 1968, v. 8, pp. 1377-1380.

Muntz W.R.A., Yellow filters and the absorption of light by the visual pigments of some Amazonian fishes, Vision. Res., 1973, v. 12, pp. 2235-2254.

Orlov O.Yu., Gamburtzeva A.G., Changeable coloration of cornea in the fish Hexagrammos octogrammus, Nature, 1976, vol. 263, pp. 405-406.

Walls G.L., Judd, H.D., The intraocular colour filters of vertebrates, Br. J. Ophthal., 1933, v. 17, pp. 641-675, 705-725.

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