Stenodus nelma has previously been considered a subspecies of Stenodus leucichthys (S. leucichthys nelma).

The typical Stenodus leucichthys (beloribitsa) is a landlocked Eurasian species restricted to the Caspian Sea basin, and now extinct in the wild.
Stenodus nelma has previously been considered a subspecies of Stenodus leucichthys (S. leucichthys nelma). 
The typical Stenodus leucichthys (beloribitsa) is a landlocked Eurasian species restricted to the Caspian Sea basin, and now extinct in the wild.
Nelma