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Corneas in different species of the greenling family Hexagrammidae can change coloration depending on the level of ambient illumination. This process is based on redistribution of carotenoid pigments in specialized chromatophores. The spectral properties of corneas and the absorbance spectra of the visual pigments in the retinal photoreceptors were measured in four species and in one inter-species hybrid of greenlings. The modifying effect of the colored corneal filters on the cone absorbance was evaluated. A positive correlation was found between the degree of the long-wave sensitivity of cones and the maximal optical density of the cornea at the same wavelengths. Comparison of the literature data on the spectral properties of photoreceptors and peculiarities of the cornea organization with the daily, seasonal, and other behavioral activities of greenlings allowed us to confirm the earlier proposal of an important light-protective role of the changeable cornea in greenlings.

The spectral sensitivity and complement of the retinal photoreceptors of the Asiatic smelt from the Sea of Japan were studied by microspectrophotometry and light microscopy. Apart from rods, one type of single cones and one type of unequal double cones were found in major parts of the retina. The dominant type of the cone pattern (mosaic) is a row pattern consisting of various linear arrangements of separate single and double cones. The absorbance maxima of rods and a majority of singe cones and double cones equaled 516, 425 and 514/565 nm, respectively. It has been established that all of the pigments are based on retinal. The findings are compared with data on the osmerid retina from the literature and discussed with respect to the adaptations to light conditions, peculiarities of behavior, and seasonal migrations of smelts.

This study revealed additional data concerning the spawning period of the Japanese anchovy Engraulis japonicus Temminck et Schlegel, 1846 in Vostok Bay (Peter the Great Bay, Sea of Japan). The spawning of E. japonicus in this area ends in September at a water temperature of 17.5 ± 3°C. Some important peculiarities of the embryonic and postembryonic development of E. japonicus in the natural environment are described. The anchovy larvae have characteristic upper and lower rows of melanophores and subcaudal paired rows of melanophores on the trunk. Regular alternating rows of long and short cones were found in the retina of the early larval stages (TL 5.5 ± 0.1 mm). The planes of the photoreceptive lamellae in the outer segments of the short cones are oriented parallel to the long cell axis, which evidently provides sensitivity to polarized light.

A full-length complementary (c)DNA encoding ultraviolet (UV)-sensitive opsin (sws1) was isolated from the retina of the Japanese sardine Sardinops melanostictus. The sws1 phylogenetic tree showed a sister group relationship with the Cypriniformes, following the ray-finned fish phylogeny. By expressing reconstituted opsin in vitro, it was determined that the maximum absorbance spectrum (λ

This study examines some peculiarities of the eye organization and spectral properties of retinal photoreceptors of the Pacific saury Cololabis saira. The saury has relatively large eyes with a developed accomodation apparatus and an area of enhanced visual acuity (the fovea) in the retina. A specialized pigmented septum is observed in the vitreal cavity, which is supposed to function as a light-shading screen. The retina contains numerous rods and single and double cones arranged in a square mosaic pattern. Microspectrophotometric measurements indicated that their max occurs at 502 (rods), 380 (single cones), and 478/565 (double cones) nm. Such properties can provide color vision in a broad spectral range, including UV light. The peripheral visual apparatus of the Pacific saury is typical of active diurnal predatory fish that inhabit shallow and upper pelagic water layers.

The spectral sensitivity of the retinal photoreceptors in 31 fish species belonging to five families from the Sea of Japan was studied by microspectrophotometry. All species inhabit the subtidal zone, often occurring at shallow depths. The photoreceptors of more than half the species had porphyropsin, which makes the retina more sensitive to long-wave light. Some species displayed a remarkable shift of spectral sensitivity to the long-wave end, which is correlated with life in shallow waters and with the presence of optically dense orange corneal filters. The results further support the notion that the presence of porphyropsin in the retina is necessary for not only freshwater fishes.

The retina of anchovies is characterized by an unusual arrangement and ultrastructure of cones. In the retina of Japanese anchovies, Engraulis japonicus, three types of cones are distributed into rows. The nasal, central, temporal, and ventro-temporal regions of the retina were occupied exclusively by the long and short cones. Triple cones, made up of two lateral components and one smaller central component, were found only in the dorsal and ventro-nasal retinal regions. In the outer segments of all short and long cones from the ventro-temporal region, the lamellae were oriented along the cell axis and were perpendicular to the lamellae in the long cones, providing a morphological basis for the detection of polarization. This lamellar orientation is unique to all vertebrates. The cones were examined with respect to regional differentiation in their size and spectral properties via light microscopy, transmission electron microscopy, and microspectrophotometry. Various dimensions of cones were measured in preparations of isolated cells. The cones from the ventro-temporal region had different dimensions than cones of the same type located in other retinal regions. Triple cones from the dorsal region were significantly larger than triple cones from the ventro-nasal region. The spectral absorbance of the lateral components of triple cones in the ventro-nasal retina was identical to the absorbance of all long and short cones from the ventro-temporal region. These are shifted to shorter wavelengths relative to the absorbance of the lateral components of the triple cones located in the dorsal retina. Thus, the retina of the Japanese anchovy shows some features of regional specialization common in other fishes that improves spatial resolution for the upwards and forwards visual axis and provides spectral tuning in downwelling light environment. That results from the differentiation of cone types by size and by different spectral sensitivity of various retinal areas.

The development of corneal staining cells (CSCs) and a changeable light filter made of CSCs was studied in the sculpin Porocottus allisi(Cottidae). It is shown that CSC development is complete within 9 days, and the whole changeable light filter system, within 11 days. The development begins with the droplike chromatophore stage. Later on, numerous processes and a projection towards the pupillary zone are formed, accompanied by the appearance of granular structures in the cytoplasm. In subsequent development, the cell becomes round. Later on, it becomes 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 changes in illumination. Light filter formation starts in the dorsonasal cornea and expands dorsally, ending in the ventral cornea 6 days after beginning. The end of light filter development coincides with the metamorphosis of the larvae, which is consistent with the peculiarities of their ecology.

It is shown, for the first time, that in both migratory salmon fry Oncorhynchus masou, and in dwarf form of this species retina reaction changes after experimental geomagnetic field (GMF) compensation, and these changes were different in migratory salmon fry and in dwarfs. The reaction of various types of retina photoreceptors in migratory salmon fry to GMF compensation differs: if the rods and double cones perceive GMF compensation as an approach of darkness (scotopic reaction), single (as a rule, blue-sensitive) cones react to GMF compensation as a presentation of dark blue or (very seldom) of ultra-violet radiation. The retina of dwarf form of salmon reacts to GMF compensation as follows: the rods demonstrate light (photopic) reaction, and double (red-green-sensitive) cones--dark (scotopic) reaction. Single (dark blue-sensitive) cones react to GMF compensation as to bright dark blue light. Thus, the morphological picture of dwarf form of salmon retina under the given experimental conditions corresponds to perception of dark blue light. The initial conditions were different and corresponded to usual scattered day time light with illumination of about 7.5 luxes. GMF compensation does not seem to influence rods, while double, red-green cones react to it as to darkness, that is the fish does not perceive red and green light of a visible spectrum, and perceives only dark blue and, probably, ultraviolet by means of central dark blue-sensitive and additional cones. Thus, it is shown, that under conditions of usual day-time illumination salmon retina photoreceptors react to change of GMF, i.e. they play a role of magnetoreceptors.

The studies reported here provide the first demonstration that retinal responses in both the fry of the migratory salmon trout Oncorhynchus masou and the dwarf form of this species changed in conditions of experimental neutralization of the geomagnetic field (GMF); migratory salmon trout fry and dwarves showed different changes. The responses of different types of retinal photoreceptor in migratory salmon trout fry to neutralization of the GMF differed: while rods and double cones perceived neutralization of the GMF as the onset of darkness (the scotopic reaction), single (generally blue-sensitive) cones responded to neutralization of the GMF both as presentation of blue light or (very rarely) ultraviolet irradiation. The retina of dwarf male salmon trout responded to neutralization of the GMF with a double response: rods showed a light (photopic) response, while double (red/green-sensitive) cones produced dark (scotopic) responses. Single (blue-sensitive) cones responded to neutralization of the GMF as bright blue light. Thus, the morphological picture of the retina in dwarf male salmon trout in these experimental conditions corresponds to the perception of blue light. The initial conditions were different — normal diffuse daylight with a brightness of about 7.5 Lx. It is likely that neutralization of the magnetic field had no effect on rods, while double, red-green, cones responded as to darkness, i.e., the fish did not perceive red or green light in the visible spectrum, but perceived only blue and, possibly, ultraviolet light by means of central blue-sensitive and accessory cones. Thus, these experiments demonstrated that in conditions of normal daylight illumination, retinal photoreceptors in salmon fry respond to changes in the earth’s magnetic field, i.e., objectively function as magnetoreceptors.

Under the conditions of behavioural experiment capacity of grey toads for constant perception of an object colour was studied. It is shown that irrespective of the spectral composition of light source toad males are able to recomgnize blue colorations among the other ones (green and grey of various gradations).

Colour vision and constancy of colour perception in Bufo bufo L, were examined by means of unconditioned reaction of choosing moving and stationary models of females by males during breeding season. The males chose blue and dark blue models. Control of the choice of blue models presented in pairs with models of different shades of grey proves the existence of colour vision in Bufo bufo L. The choice of blue models has been observed under significantly varying conditions: both with artificial illumination and in sunlight. This attests the capacity of toads for constant colour perception. When a model was presented against a saturated red background, colour contrast was observed: under such conditions the toads chose the grey models which evoked no reactions when presented against white background.