Salmonidae in the context of Chalk stream

Salmon (/ˈsæmən/; pl.: salmon) are any of several commercially important species of euryhaline ray-finned fish from the genera Salmo and Oncorhynchus of the family Salmonidae, native to tributaries of the North Atlantic (Salmo) and North Pacific (Oncorhynchus) basins. Salmon is a colloquial or common name used for fish in this group, but is not a scientific name. Other closely related fish in the same family include trout, char, grayling, whitefish, lenok and taimen, all coldwater fish of the subarctic and cooler temperate regions with some sporadic endorheic populations in Central Asia.

Salmon are typically anadromous: they hatch in the shallow gravel beds of freshwater headstreams and spend their juvenile years in rivers, lakes and freshwater wetlands, migrate to the ocean as adults and live like sea fish, then return to their freshwater birthplace to reproduce. However, populations of several species are restricted to fresh waters (i.e. landlocked) throughout their lives. Folklore has it that the fish return to the exact stream where they themselves hatched to spawn, and tracking studies have shown this to be mostly true. A portion of a returning salmon run may stray and spawn in different freshwater systems; the percent of straying depends on the species of salmon. Homing behavior has been shown to depend on olfactory memory.

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.

Salvelinus is a genus of salmonid fish often called char or charr; some species are called "trout". Salvelinus is a member of the subfamily Salmoninae within the family Salmonidae. The genus has a northern circumpolar distribution, and most of its members are typically cold-water fish that primarily inhabit fresh waters. Many species also migrate to the sea.

Most char may be identified by light-cream, pink, or red spots over a darker body. Scales tend to be small, with 115–200 along the lateral line. The pectoral, pelvic, anal, and the lower aspect of caudal fins are trimmed in snow white or cream leading edges.

Thymallus, commonly known as graylings, is a genus of freshwater ray-finned fish and the only genus within the subfamily Thymallinae of the family Salmonidae. Although all Thymallus species can be generically called graylings, without specific qualification the term "grayling" typically refers to the type species Thymallus thymallus, the European grayling.

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.

Micropterus is a genus of North American freshwater fish collectively known as the black bass, which belong to the sunfish family Centrarchidae of order Centrarchiformes. They are sometimes erroneously called "black trout", but the name trout more correctly refers to certain potamodromous members of the family Salmonidae (order Salmoniformes).

Micropterus are widely distributed east of the Rocky Mountains, from the Hudson Bay basin in Canada to northeastern Mexico. Several species, notably the largemouth and smallmouth bass, have been very widely introduced throughout the world, and are now considered cosmopolitan. All black bass species are highly sought-after game fish and well known as strong fighters when hooked, and bass fishing is an extremely popular outdoor sport throughout their native range. Their meat is quite edible and firm, although they are not regarded as commercial food fish.

The Atlantic salmon (Salmo salar) is a species of ray-finned fish in the family Salmonidae. It is the third largest of the Salmonidae, behind Siberian taimen and Pacific Chinook salmon, growing up to 1 m (3.3 ft) in length. Atlantic salmon are found in the northern Atlantic Ocean and in rivers that flow into it. Most populations are anadromous, hatching in streams and rivers but moving out to sea as they grow where they mature, after which the adults seasonally move upstream again to spawn.

When the mature fish re-enter rivers to spawn, they change in colour and appearance. Some populations of this fish only migrate to large lakes, and are "landlocked", spending their entire lives in freshwater. Such populations are found throughout the range of the species. Unlike Pacific species of salmon, S. salar is iteroparous, which means it can survive spawning and return to sea to repeat the process again in another year with 5–10% returning to the sea to spawn again. Such individuals can grow to extremely large sizes, although they are rare. The different life stages of the fish are known by several different names in English; alevin, fry, parr and smolt.

Salvethymus svetovidovi, also called the long-finned charr, is a species of salmonid fish. It is endemic to Elgygytgyn Lake in Chukotka, Far East of Russia, together with two other species, the small-mouth char Salvelinus elgyticus, and the Boganid char, Salvelinus boganidae.

A kype is a hook-like secondary sex characteristic which develops at the distal tip of the lower jaw in some male salmonids prior to the spawning season. The structure usually develops in the weeks prior to, and during, migration to the spawning grounds. In addition to the development of the kype, a large depression forms in the two halves of the premaxilla in the upper jaw, allowing the kype to fit into the premaxilla when the mouth is closed.

The kype functions as a secondary sexual characteristic and influences the formation of dominance hierarchies at the spawning grounds. The size of the kype is believed to determine male spawning frequency.

Spotted seatrout (Cynoscion nebulosus), also known as speckled trout, is a common estuarine fish found in the southern United States along coasts of Gulf of Mexico and the coastal Atlantic Ocean from Maryland to Florida. While most of these fish are caught on shallow, grassy flats, spotted seatrout reside in virtually any inshore waters, from the surf of outside islands to far up coastal rivers, where they often come for shelter during cold weather. Contrary to its name, the spotted seatrout is not a member of the trout family (Salmonidae), but of the drum family (Sciaenidae). It is popular for commercial and especially recreational fishing in coastal waters of the southeastern United States. Adults reach 19–37 inches in length and 3–17 pounds in weight.

The brook trout (Salvelinus fontinalis) is a species of freshwater fish in the char genus Salvelinus of the salmon family Salmonidae native to Eastern North America in the United States and Canada. Two ecological forms of brook trout have been recognized by the US Forest Service. One ecological form is long-lived potamodromous populations in Lake Superior known as coaster trout or coasters. The second ecological form is the short-living predaceous anadromous populations which are found in northern lakes and coastal rivers from Long Island to Hudson Bay, which are referred to as salters. In parts of its range, it is also known as the eastern brook trout, speckled trout, brook char (or charr), squaretail, brookie, or mud trout, among others. Adult coaster brook trout are capable of reaching sizes over 2 feet in length and weigh up to 6.8 kg (15 lb), whereas adult salters average between 6 and 15 inches in length and weigh between 0.5 and 2.3 kg (1 and 5 lb). The brook trout is characterized by its distinctive olive-green body with yellow and blue-rimmed red spots, white and black edged orange fins, and dorsal vermiculation. The diet of the brook trout is restrictive to the season and location of the fish, but will typically consist of terrestrial and aquatic insects, fry, crustaceans, zooplankton, and worms.

Throughout history, non-native brook trout have been transplanted beyond its native borders, where it has spread across North America and much of the world. These brook trout have been introduced since the 1800s by means of artificial propagation and aquaculture in hope of promoting fishery resources. Through this transplantation, brook trout have been observed to affect native populations by outcompeting, preying upon, and hybridizing with many native aquatic species. This invasive nature via human-mediated introductory has led to their classification in the list of the top 100 globally invasive species.

Thymallus thymallus, the grayling or European grayling, is a species of freshwater fish in the salmon family Salmonidae. It is the only species of the genus Thymallus (the graylings) native to Europe, where it is widespread from the United Kingdom and France to the Ural Mountains in Russia, and Balkans on the south-east, but does not occur in the southern parts of the continent. It was introduced to Morocco in 1948, but it does not appear to have become established there.