Salmo is a genus of ray-finned fish from the subfamily Salmoninae of family Salmonidae, and is part of the tribe Salmonini along with the sister genera Salvelinus and Salvethymus. Almost all Salmo species are native only in the Old World (including most of Europe, coastal North Africa and part of West Asia around the Black Sea), the only exception being the Atlantic salmon (Salmo salar), which is also naturally found across the North Atlantic in eastern North America.

The number of distinct species and subspecies in Salmo is a debated issue. The Atlantic salmon and brown trout (Salmo trutta) are widespread species and have been introduced worldwide as farmed food fish or recreational game fish, while most of the other Salmo species are narrowly distributed forms endemic to single watersheds.

The name Salmo derives from the Latin salmō, meaning salmon. The vast majority of the Salmo species are actually trout, except the Atlantic salmon, which along with six Pacific species from the genus Oncorhynchus (also from the subfamily Salmoninae, but of a different tribe) constitute the only seven officially recognized species of salmon.

Only two fossil species are known: †Salmo immigratus Gorjanovic-Kramberger, 1891 from the Miocene of Croatia, and †Salmo derzhavini Vladimirov, 1946 from the late Pliocene of Armenia. S. immigratus was initially dated to the Late Miocene, though more recent analyses suggest that it may date to the Middle Miocene, or the regional Sarmatian stage. S. immigratus appears to be a basal member of the genus, while S. derzhavini represents the earliest known occurrence of the brown trout species complex.

...