Salmoninae in the context of Fish scale

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.

Oncorhynchus, from Ancient Greek ὄγκος (ónkos), meaning "bend", and ῥύγχος (rhúnkhos), meaning "snout", is a genus of ray-finned fish in the subfamily Salmoninae of the family Salmonidae, native to coldwater tributaries of the North Pacific basin. The genus contains sixteen extant species, namely six species of Pacific salmon and ten species of Pacific trout, all of which are migratory (either anadromous or potamodromous) mid-level predatory fish that display natal homing and semelparity.

The name of the genus is derived from Ancient Greek ὄγκος (ónkos), meaning "bend", and ῥύγχος (rhúnkhos), meaning "snout", in reference to the hooked secondary sexual characteristic — known as the kype — that the males develop on the lower jaw tip during mating season.

Trout (pl.: trout) is a generic common name for numerous species of carnivorous freshwater fishes belonging to the genera Oncorhynchus, Salmo, and Salvelinus, all of which are members of the subfamily Salmoninae in the family Salmonidae. The word trout is also used for some similar-shaped but non-salmonid fish, such as the spotted seatrout/speckled trout (Cynoscion nebulosus, which is actually a croaker).

Trout are closely related to salmon and have similar migratory life cycles. Most trout are strictly potamodromous, spending their entire lives exclusively in freshwater lakes, rivers and wetlands and migrating upstream to spawn in the shallow gravel beds of smaller headwater creeks. The hatched fry and juvenile trout, known as alevin and parr, will stay upstream growing for years before migrating down to larger waterbodies as maturing adults. There are some anadromous species of trout, such as the steelhead (a coastal subspecies of rainbow trout) and sea trout (the sea-run subspecies of brown trout), that can spend up to three years of their adult lives at sea before returning to freshwater streams for spawning, in the same fashion as a salmon run. Brook trout and three other extant species of North American trout, despite the names, are actually char (or charr), which are salmonids also closely related to trout and salmon.

The freshwater whitefish are fishes of the subfamily Coregoninae, which contains whitefishes (both freshwater and anadromous) and ciscoes, and is one of three subfamilies in the salmon family Salmonidae. Apart from the subfamily Coregoninae, the family Salmonidae includes the salmon, trout, and char species of the subfamily Salmoninae, and grayling species of the subfamily Thymallinae. Freshwater whitefish are distributed mainly in relatively cool waters throughout the northern parts of the Northern Hemisphere.

Hucho is a genus of large piscivorous salmonid fish known as taimens (from Finnish taimen, 'trout', through Russian: тайме́нь, romanized: taĭménʹ), and is closely related to Pacific trout and lenoks (all belonging to the same tribe in the subfamily Salmoninae). Native to the cold rivers and other freshwater habitats in Eurasia, they are threatened by overfishing and habitat loss.

The earliest fossil remains of this genus are known from the Late Oligocene to middle Miocene of the Vitim Plateau in Russia. Younger remains are also known from the Late Miocene of Ukraine and the Late Pleistocene of Germany. Fossil specimens of a Hucho-like salmonid have been recovered from the Clarkia fossil beds and other localities from the late Neogene of western North America, suggesting they may have potentially inhabited North America too.