Trout is the common name given to a number of species of freshwater fish belonging to the salmon family (Salmonidae).

All fish properly called trout are members of the subfamily Salmoninae, but the name is used for fish from all three genera in the subfamily: Salmo, which includes Atlantic species; Oncorhynchus, which includes Pacific species; and Salvelinus, which includes fish referred to as Char. Fish referred to as trout include:

  • Genus Salmo
    • Adriatic trout – Salmo obtusirostris
    • Brown Trout -Salmo trutta
    • Flathead trout – Salmo platycephalus
    • Ohrid trout – Salmo letnica
    • Sevan trout – Salmo ischchan
  • Genus Oncorhynchus
    • Apache trout
    • Cutthroat trout
    • Gila trout
    • Golden Trout
    • Rainbow trout
  • Genus Salvelinus (Char)
  • Brook Trout
  • Bull trout
  • Dolly Varden trout
  • Lake trout
  • Silver trout (extinct)

Trout are usually found in cool, clear streams and lakes, and are distributed throughout North America, northern Asia and Europe. Several species of trout were introduced to Australia and New Zealand by amateur fishing enthusiasts in the 19th century, which contributed to the displacement of several native freshwater fish to some extent.

Trout have no spines on the fins, and all of them have a small, adipose (fatty) fin along the back, near the tail. There are many species, and even more populations that are isolated from each other and morphologically different. However, many of these distinct appearing populations show no significant genetic differences, and therefore what appear to be a large number of species are considered a much smaller number of distinct species by most ichthyologists.

The trout found in the eastern United States are a good example of this. The brook trout, the aurora trout and the (extinct) silver trout all have physical characteristics and colorations that distinguish them apart from others. Genetic analysis shows however that they are one species, Salvelinus fontinalis.

Lake trout (Salvelinus namaycush), like brook trout, are actually a member of the char genus. It inhabits many of the larger lakes in North America and lives much longer than Rainbow trout which has an average maximum life span of 7 years. Lake trout can live many decades and can grow to more than 60 pounds.

Most trout are restricted to freshwater, but many, like the steelhead (Oncorhynchus mykiss) – which is the same species as the landlocked rainbow trout – spend their adult life in the ocean and then return to spawn in the streams in which they were hatched. This is called anadromous reproduction and is more often seen in salmon. Brook trout, Brown trout, Cutthroat trout, Bull trout, and Arctic char also have populations that run to salt water.

Trout generally feed on soft bodied aquatic invertebrates, such as Diptera, mayfly, caddis fly, and stonefly, although larger specimens of trout regularly feed on other fish.

As a group, trout are a somewhat bony fish, but the flesh is considered good eating. Additionally, they provide a good fight when caught with a hook and line, and are sought after recreationally. Because of their popularity, trout are often raised on fish farms and introduced into the streams that are most heavily fished. While they can be caught with a normal rod and reel, fly fishing is a distinctive method developed primarily for trout and now extended to other species. Farmed trout and char are also sold commercially.

The cutthroat trout has 14 recognized subspecies (depending on your sources), such as the Lahontan cutthroat trout Oncorhynchus clarki henshawi, Bonneville cutthroat trout Oncorhynchus clarki utah, Colorado River cutthroat trout, Yellowstone cutthroat trout.