Comparative histological study of eye cornea in three fresh water bone fishes

Abstract<br /> The present study carried out to investigate the comparative histological structure of the eye cornea for three species of fresh water teleosts fishes at the level of light microscope. The three species belong to two different families .The species studied were Garra lamta, Acanthobrama marmid and Mastacembelus simach. These species live in different photic aquatic environments, as well as differ in feeding nature.<br /> The results reveald that the cornea, of the three species, comprises two different structural regions: the peripheral and the central. Generally the histological structure of the cornea include a layer of non-keratinized stratified squamous epithelium. The epithelium was settled on a thin membrane called Bowman's membrane. Alternative to Bowman's membrane the corneal stroma, which differs in number, nature and thickness of the collagenous fibres among the three species and intraocularly.The stroma settled on a thin Descemet membrane which lining with a single layer of endothelium.<br /> The peripheral cornea reveald wide different structural specializations among the three species and also differ in various ocular regions in the same species. The first specialization was the appearance of mucous (goblet) cells which presents in the corneal epithelium of G. lamta and A. marmid only .The second specialization was the annular ligament which appeared in the three species and differ in shape, thickness and stain among the three species as well as intraocularly. On the other hand, the annular ligament may be reduced or absent. The annular ligament of the M. Simach only comprise the blood capillaries.<br /> The third specialization was the appearance of autochthonous layer in the cornea of A. marmid only, which differ in the thickness and stain in the different regions of the eye ball.<br /> <br /> *البحث مستل من رسالة ماجستیر للباحث الثانی وبإشراف الباحث الأول. <br /> The stroma showed wide variations in it'sthickness and components among the three species and in the eye ball of the same species. The stroma of G. lamta was composed of dermal and scleral portions. The scleral one more dense in staining than the dermal. In the A. Marmid the stroma very thick and the scleral portion more lucident. The stroma of A. marmid showed atransverse sutures in the dermal and in some parts of scleral. In M. simach, there were wider variations in the inner layers of peripheral cornea. The dorsotemporal region was very thickness and consists of additional layers, in that the sclera composed of dermal portion and the scleral stoma was divided into posterior and anterior portions. In addition mucoid lucident layer and iridescent layer added in the dorsotemporal region as well as a melanophores (colour filter) and a muscle inserted in the iris root. One of the most important specializations were the presence of primary spectacles in M. simach and secondary spectacles in the A. marmid but not in G. lamta.