Retinal morphology and retinomotor response in Caspian kutum (Rutilus frisii subsp. kutum)

In this study, the morphology and organization of the retina of Caspian kutum and fish response to ambient light as retinomotor reaction was investigated. The Rutilus frisii subsp. kutum is an anadromous fish and important native fish specimen of Caspian Sea. The specimens were obtained from Shahid Ansari Teleost Reproduction and Culture center (Guilan province, Iran). For light and dark adaptation fish were left in dark and light at least 30 minute prior to death. The eye retina were dissected out and processed for histological and SEM studies. The eye retina of Caspian kutum like most vertebrates, was composed of ten layers. Two types of photoreceptor cells including rod and short single cone were identified. Sagittal and transverse retinal sections did not show any particular patterns of cone arrangement. The retinomotor response observed in adapted retina to light and dark conditions revealed that Caspian kutum strongly reacts to changing light conditions. A remarkable pigment index indicated kutum relied mostly on rod rather than cone vision. The movement of pigment granules and slight change of cone myoid showed that the fish could recognize colors.