Structure and arrangement of photoreceptors in the retina of Alosa braschnikowi (Borodin, 1904)

Document Type : Research Paper


1 Department of Marine Biology, University of Gonbadkavoos, Iran

2 Department of Biology, University of Guilan, Iran

3 Department of Biology, University of Gonbadkavoos, Iran

4 Department of Biology, University of Gonbadkavoos, Iran.


In order to identify the visual characteristics of pelagic fish eye  and their eye relationship with feeding and living environment, Alosa braschnikowi in the west part of north of Caspian Sea was investigated. The eye of male fishes with the average weight of 338±10g were prepared for histological and SEM studies. Three types of light receiving cells including rod, short single cone and twin cone were identified. Tangential retinal sections showed that the diameter of cone cells decreased from periphery to the center. The density of twin cone cells from the ventro-temporal quadrant to dorso-temporal quadrant decreased clockwise orderly and the average of cells' diameter increased in the mentioned sections of retina. The arrangement of cells in dorsal quadrants and in the periphery ventral quadrants followed row mosaic pattern whereas in the central parts of ventral quadrants they were arranged in square mosaic pattern. According to the previous studies, the presence of the square pattern assisted visual acuity, identifying the polarized light and hunting skills. Thus Alosa braschnikowi possess remarkable sight to the up, front and rear orientations. Moreover dorsal quadrants would increase the light sensitivity of fish eye in low light illumination of deeper waters.