Stenodus leucichthys, also known as the inconnu, sheefish, ak balyk, or beloribitsa, is a species of large, anadromous, freshwater whitefish in the family Salmonidae.

Stenodus leucichthys is an anadromous fish, meaning it migrates up stream into fresh waters from the sea in order to spawn and reproduce externally.

Migrations can last up to or exceeding a year long, this is partially owing to the slow development of their gonads which can require up to 8 months spent in the river to fully mature, just in time for their spawning season.

However, 30-day old fingerlings stomach contents have been observed to contain the larvae and juveniles of smaller fish species, indicating that this predatory transition occurs during very early life stages.

As an adult, its primary food source, comprising over 90% of its diet, is small pelagic fish which mainly consisted of native kilka and silverside, with less reliance on Caspian roach and gobiids, prior to its extirpation.

[12] Alternatively, the closely related nelma has a broad, arctic and sub-arctic distribution extending from northern Eurasia to north-west North America.

[2][9] It is euryhaline given its anadromous spawning migration, allowing them to survive in fresh and brackish waters with increased salinity tolerances developing in fingerlings around the age of 30 to 50 days.

While this ban was lifted in the 1980s due to artificial reproduction efforts, it was reestablished because of continued population decline from illegal fishing, river contamination, and hatcheries releasing fewer fingerlings.

[2] The widespread, closely related Stenodus nelma is a historically important subsistence food for Native Alaskans in the Yukon and Mackenzie River basins.