Abstract
The nervous system and its development play a crucial role in fish survival, locomotion and adaptation. Rutilus frisii kutum is one of the ecologically and economically important fish species of the Caspian Sea which is annually cultured and released in the Caspian Sea as millions of fingerlings. In order to investigate the nervous system structure of the Caspian Kutum, Rutilus frisii kutum, fingerlings were studied through histology technique. Results showed that the nervous system of the fingerlings is well developed, and composed of central (brain and spinal cord) and peripheral (nerves and ganglia) nervous tissue. The brain showed the normal structure of a ray-finned bony fish as in other teleosts, which shows that the fingerlings have the complete nervous system for facing and adapting to the new environment after release to the sea.