Ontogeny of the eye of Caspian kutum (Rutilus frisii kutum) from prehatch to final larval stage

The present study examines the developmental stages of the eye retina in Caspian kutum during the pre-hatch stage to end of the larval stage. Fertilized eggs of Caspian kutum were obtained from Shahid Ansari Center for Reproduction of teleost fish (Guilan province, Iran). Sampling was done for one month until the larval stage completed and the yolk sac completely depleted. Samples were studied by optical and electron microscopy. On day3 (68hpf) post fertilized embryo the primary optic structure was observed. The undifferentiated neural epithelium was placed around the lens placode originated from ectoderm. At (120hpf) 5dpf, the eye was spherical and the optic cup was formed. The first retinal stratification was initiated at the (216h.dpf) 9dpf and  cone cells appeared in the retina, while rod cells that only function in low light conditions, appeared after hatching at the fourth post hatching day. Cellular arrangement continued until several days after hatching. Along with the growth and development of the eye, the lens grew by addition of secondary lens fiber cells proliferated from lens epithelium cells. Also the primary lens fiber losing nuclei and other membranous intracellular organelles. The results obtained from the diameter of the lens and the cone density represented that visual acuity of Caspian kutum larvae increased at the end of larval stage.