الملخص

The present Study Conducted to investigate the morphological, anatomical and histological development photoreceptors development in viviparous teleost fish Xiphophorus maculates at the level of light microscope. The results showed the embryonic development of the photoreceptors in the retina started at early stage.The differentiation and development progressed to form aduplex retina which is avascular and including eight layers and two membranes at adult stage. The first signal of photoreceptors initiation as rods and cones nuclei appeared at the 3rd stage of development. Variations appeared in the rods development and differentiations in their partitions. In addition, the number of rods increased compared to that of cones, to reach the ratio of 4:1 in the adult stage. On the other hand, the cones developed into four main types and their partitions differentiated. The first two types differentiated were long single and twin cones.