The sterlet (Acipenser ruthenus) is a relatively small species of sturgeon from Eurasia native to large rivers that flow into the Black Sea, Azov Sea, and Caspian Sea, as well as rivers in Siberia as far east as Yenisei. Populations migrating between fresh and salt water (anadromous) have been extirpated.Due to overfishing (for its flesh, caviar, and isinglass), pollution, and dams, the sterlet has declined throughout its native range and is considered vulnerable by the IUCN.