brown trout

brown trout
Name	Brown trout
Taxon	Salmo trutta
Authority	Linnaeus, 1758
Range map caption	Native range (blue), introduced range (red)

Brown trout is a Eurasian species of salmonid fish that has been widely introduced globally. It is highly valued in recreational fishing and is known for its wariness and strength, making it a prized catch for anglers. The species exhibits considerable morphological variation across its range, leading to numerous described subspecies and forms, such as the migratory sea trout.

Description and taxonomy

The species was first formally described by Carl Linnaeus in his seminal work Systema Naturae. Its scientific name, Salmo trutta, places it within the genus Salmo, which it shares with the Atlantic salmon. Physical characteristics vary significantly; riverine forms, often called river trout, are typically more streamlined and darker, while lacustrine forms can grow larger and develop more pronounced kypes. Notable subspecies include the Adriatic trout of the Balkan Peninsula and the Aral Sea trout. The complex taxonomy has been clarified through modern genetic analysis, including studies of mitochondrial DNA.

Distribution and habitat

Native to Europe, western Asia, and northwestern Africa, the brown trout has been introduced to every continent except Antarctica. Successful introductions began in the 19th century, notably to New Zealand, Australia, South Africa, and the United States, including states like Montana and Argentina's Patagonia region. It thrives in cool, well-oxygenated waters, inhabiting diverse environments from small headwater streams and large rivers like the River Thames to deep, cold lakes such as Loch Ness and high-altitude alpine lakes. It is less tolerant of warm, silt-laden waters compared to some North American species.

Life cycle and behavior

The life history is flexible, with both resident and migratory populations. Migratory forms, known as sea trout, undertake journeys to marine environments, similar to the anadromous behavior of Atlantic salmon. Spawning occurs in gravel redds during autumn and winter, with females excavating nests in swift-flowing tributaries. After hatching, the alevin remain in the gravel before emerging as fry. Individuals can be highly territorial, especially in stream environments, often holding specific lies behind rocks or under undercut banks. Notable for their longevity, some individuals in lakes like Lake Windermere have been recorded living over 20 years.

Diet and feeding

As opportunistic predators, brown trout have a varied diet that shifts with age and habitat. Juveniles primarily consume aquatic insect larvae, such as those from the orders Ephemeroptera, Trichoptera, and Plecoptera. Larger adults are piscivorous, preying heavily on other fish like minnows, sculpin, and in introduced ranges, rainbow trout and salmon parr. They also consume terrestrial insects, amphipods, and even small mammals. Their feeding behavior is often studied in the context of optimal foraging theory, and they can significantly impact native fish communities in non-native ecosystems.

Relationship with humans

The brown trout is one of the world's most iconic game fish, central to the culture of fly fishing celebrated in works like those of Izaak Walton's The Compleat Angler. It supports substantial recreational fisheries in regions from the English Lake District to the Rocky Mountains. Commercially, it is raised in aquaculture facilities across Norway, Scotland, and Chile for both restocking and food. It holds a place in heraldry, featuring on the coats of arms for towns like Trutnov in the Czech Republic, and is the subject of conservation organizations like the Wild Trout Trust.

Conservation status

Globally, the species is listed as Least Concern on the IUCN Red List due to its extensive introduced range. However, many native populations face significant threats, including habitat degradation from agriculture, river engineering projects like those on the River Danube, competition and hybridization with introduced Atlantic salmon, and the impacts of climate change on water temperature. Conservation efforts are spearheaded by entities like the Environment Agency and involve habitat restoration, the creation of fish passages, and strict angling regulations regarding catch and release.

Category:Salmonidae Category:Fish of Europe Category:Game fish Category:Taxa named by Carl Linnaeus