Stenodus leucichthys

Stenodus leucichthys, also known as the inconnu, sheefish, ak balyk, or beloribitsa, is a species of large, anadromous, freshwater whitefish in the family Salmonidae. In the strict sense its natural distribution is restricted to the Caspian Sea basin. It was formerly considered extinct in the wild, but survives in cultured stocks. The nelma (Stenodus nelma), a more widespread species of Eurasia and North America, is sometimes considered its subspecies.