The sterlet (Acipenser ruthenus) is a relatively small species of sturgeon native to the Black Sea, Azov Sea, and Caspian Sea, as well as rivers in Siberia.
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. Restocking projects are ongoing, and it has been introduced to some regions outside its native range, but the latter have generally not become self-sustaining. Today, the majority of the international trade involves sterlets from aquaculture.