Abstract: The study was undertaken to illustrate the variation of eye size, its relative area in relation to the head and genetic variations of the isoenzymes of lactic dehydrogenase and glucose-6-phosphate dehydrogenase in three freshwater fishes. These are Bagrus bajad (Forsskål, 1775, order: Siluriformes and Family: Bagridae), Labeo niloticus (Forsskål, 1775, order: Cypriniformes and Family: Cyprinidae) and Lates niloticus (Linnaeus, 1758, order: Perciforms and Family: Centropomidae) were captured from River Nile of Egypt and investigated for position of eye and their surface area in relation to head region as well as investigated the retina iso-enzyme electrophoresis to predicted the activity and genetic variations. The study revealed that the average percentage of eye size was increased in Bagrus baja in comparison with Lates niloticus and Labeo niloticus. Bagrus bajad is nocturnal fish. The protrusion and localization of eye in the front of the head region reflected the accommodation to its carnivorous feeding. The isoenzyme fractions of lactic dehydrogenase and glucosde-6-phosphate dehydrogenase varied between the studied fishes. Finally the author concluded that the eye's size and position in the head region represented the habit of feeding and accommodation to the environment. Also, the expression of lactic dehydrogenase and glucose-6phosphate dehydrogenase retinal isoenzymes represented the genetic differences between the studied fishes.