Trout is a group name for fishes belonging in the family Salmonidae. Trout are characterized by being very sensitive to environmental disruption, and are often used as indicator species to monitor rivers and lakes. Most trout are freshwater fish, although some venture out to sea for part of their life cycle. In addition to being found wild in many parts of the world, trout are also commercially farmed for sport fishing and human consumption.

Trout have been eaten for hundreds of years in a wide variety of ways, and the sweet white flesh of the fish is prized for saute especially. Trout can also be eaten very simply, with a simple sprinkling of lemon and salt, because the flesh is usually flavorful enough on its own.

Trout have elongated bodies, and a small adipose fin which grows between the dorsal and tail fins. Trout have large mouths which are carried forward, rather than lower on the head like some river fish, and can be speckled, striped, or blotched in a rainbow of colors, depending upon the species. Like most fish, trout are more pale on the underside.

Trout are often confused with their close relatives, salmon, and in fact the two fish share many similar characteristics. Even experienced anglers have been known to mistake younger representatives of both types of fish for each other. Inspecting the anal fin of the fish, located on the underside of the body before the tail fin, can be one way to tell the difference: trout have 12 or fewer rays. In addition, many trout including the steelhead have dark mouths, rather than the silver mouths of salmon, although it may be too late for the fish by the time this has been detected.

Trout require clean, free flowing water with plenty of oxygenation. In areas which have been disturbed by humans, the habitat requirements of trout are often not met and the fish begin to suffer. As a result, many environmental organizations monitor trout populations to ensure that rivers and streams are healthy, because while some trout spend part of their lives at sea, all trout return to the river to spawn in the spring.

Some trout have taken well to commercial farming, and are farmed to take the stress off wild populations. Farmed trout are also sometimes released to replenish wild populations, and numerous sport fishing organizations sponsor this so that sport fishermen can continue to pursue trout. Trout fishing is usually done with flies, and is considered by some to be an excellent way of whiling away a day at the river.