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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 sub-family: Salmo, which includes Atlantic species; Oncorhynchus, which includes Pacific species; and Salvelinus, which includes fish referred to as char or charr.


 

Trout are usually found in cool, clear streams and lakes, and are distributed naturally 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, effectively displacing several upland native fish species.


Trout have fins entirely without spines, 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 populations show no significant genetic differences, and therefore what may appear to be a large number of species is 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 colourations that distinguish them, yet genetic analysis shows that they are one species, Salvelinus fontinalis.


Lake trout (Salvelinus namaycush), like brook trout, actually belong to the char genus. Lake trout inhabit many of the larger lakes in North America and live much longer than rainbow trout which have an average maximum life span of 7 years. Lake trout can live many decades and can grow to more than 60 pounds (27 kg).

Most trout are restricted to fresh water, but many 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 somewhat bony, but the flesh is generally considered to be tasty. 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 planted into heavily fished waters in an effort to mask the effects of overfishing. 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 as food fish.

Trout that live in different environments can have dramatically different colorations and patterns. Mostly, these colors and patterns form as camouflage, based on the surroundings, and will change as the fish moves to different habitats. Trout in, or newly returned from the sea, can look very silvery, while the same "genetic" fish living in a small stream or in an alpine lake could have pronounced greenish speckles with far more coloration. It is virtually impossible to define a particular color pattern as belonging to a specific breed, however, in general, wild fish are claimed to have more vivid colors and patterns.

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 Kingdom: Animalia

 Phylum: Chordata

 Class: Actinopterygii

 Superorder: Protacanthopterygii

 Order: Salmoniformes

 Family: Salmonidae