[Photoreceptors and visual pigments of Black Sea elasmobranchs]

The retina of rays Dasyatis pastinaca and Raja clavata, as well as the dogfish Squalus acanthias was studied by electron microscopy, light colour differentiation technique and by electrophysiological methods. The retina of D. pastinaca contains about one cone per four rods. Cone and rod outer segments exhibit the ultrastructure typical of those cells in higher vertebrates. After treatment by Hartwig's method [5], cone outer segments are stained by thiasine red, rod outer segments sorbed the water-blue dye. The retina possesses both the scotopic and photopic systems, the latter reveals colour vision. With the method based on the registration of the early receptor potential it has been shown that D. pastinaca has three visual pigments with the absorption maxima near 540, 502 and 476 nm. The retina of R. clavata and S. acanthias contains only rhodopsin with lambda max= =495--497 nm. Photoreceptors of these animals are typical rods. Literature data on the Cyclostomes and results obtained for Elasmobranchs indicate that the photopic vision is phylogenetically more ancient than the scotopic system.