Visual Adaptations of the <i>Dicentrarchus punctatus</i> : New Insights Into Its Retina Adaptations With Transmission Electron Microscopy Analysis

This study was designed to illustrate the light and electron microscopic characterisations of the eye of Dicentrarchus punctatus with new insight into transmission electron microscopic features of the retina. The eye is composed of three layers: the external sclera-cornea layer, the middle layer, and the internal layer. The cornea has three laminae: stratified epithelial cuboidal cells anteriorly, Bowman (middle), and the dermato-stromal lamina posteriorly. The mucoidal lamina was observed between the cranial part of the sclera-corneal and the derma-stromal, and established by the fibre bundles of the collagen implanted in the loose connective tissue, while the iridescent lamina was found between the cranial and the caudal sclera-stromal lamina. SEM observation revealed that the cornea consisted of rounded or ovoid-shaped cells that were joined to each other by microridges. The retina is consisted of ten layers. The retina had two regions: nervous and non-nervous. The retina had both rods and cones (single, double, and triple) photoreceptor cells. The inner segment of the rod had numerous large, round mitochondria with electron-dense granules and melanin pigment extended between the ellipsoid units, while the outer segment had stacks of discs. The cone's inner segments had ellipsoids that showed mitochondria with electron-dense granules and melanin pigment extended between the ellipsoid units, in addition to disintegrated cristae. Finally, the double and triple cone cells with ellipsoids played a key role in extending the light's accessible absorption area.