الفهرس 
Chapter I Introduction & Aim Of The WorkOnly 14 pages are availabe for public view
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Abstract
Vision varied between fishes depend on living at water depths and nocturnal and diurnal condition. The anatomical structure of retina reflecting the visual acuity of freshwater fishes paid attention of many workers to study the teleost retina. Three kinds of freshwater fishes; Bagrus bajad, Labeo niloticus and Lates niloticus were collected from River Nile at Mansoura Governorate. The fishes were sacrificed and ocular regions were separated and dissected for separating the retina. The retinas were subjected for light and transmission electron microscopy, biochemical analysis (dopamine, serotonin, ATPase, LDH and G6PDH), immunohistochemistry (PCNA and synaptophysin) and isoenzyme electrophoresis of LDH and G6PDH. In the studied teleost fishes, the retinal pigment epithelium (RPE) is consisted of a single layer of closely packed polygonal cells. These cells have large basal vesicular nuclei, well developed smooth endoplasmic reticulum, mitochondria and melanosomes. The melanosomes are more abundant in Bagrus bajad and Labeo niloticus and less distributed in Lates niloticus. Retinal pigment epithelium lied in between the photoreceptors and the choroid with characteristic blood capillaries forming the blood-retinal barrier. Their apical villous structures become in contact with the photoreceptor outer segment. The cytoplasm of Bagrus bajad possessed phagocytized detached parts of the outer segments. Investigating the photoreceptors, revealed that the fishes possessed radially arranged photoreceptors. In Bagrus bajad, the photoreceptors are composed mainly of radially oriented elongated slender rods infiltrated by melanosomes. The thickness of each rod reached 3 µm thick and is traversed by finely arranged stacked lamellar membranes. However, in Labeo niloticus and Lates niloticus, the retinal photoreceptors are consisted mainly of cones with average thickness of 5.5-6 µm. The cones are composed of an inner (ellipsoid) segment containing electron-dense mitochondria, which are arranged along the long axis of the inner segment. The outer segment composed of regular stacked disc of concentric membranes of light and dense zones. The basal margin of both cones and rods are interdigitated with Muller cells. The inner segment appeared in the proximal end of photoreceptor outer segment. The outer lining layer is the ganglion cells which become more dense and of varying sizes in Labeo niloticus in comparison with the other studied fishes. The ganglion layer showed abundant neuronal processes and nerve fiber in the studied fishes. LDH isoenzymes showed a close similarities of the studied species and composed of three isoenzyme fractions. The first and second isoenzyme fractions are similar in the studied fishes. However, fraction three showed high flow rate in Labeo niloticus and decreased flow rate in Lates niloticus in comparison with Bagrus bajad . On the other hand, G-6PDH expressed four isoenzyme fractions with nearly similar intensities and distribution in the studied fishes.