|Researched by||Ruby Nash||Refereed by||This information is not refereed|
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Salmo trutta are commonly 30 cm to 50 cm in length and can weigh up to 50 kg. It is a very diverse species and has many variants including the riverine trout, lacustrine trout and sea trout. Its body colour depends greatly on its habitat. River variants have brown to yellowish sides and sea variants have silverish sides. The belly is white and dark spots surrounded by a pale halo can be seen above and below the lateral line. There are few scales and the upper part of its jaw extends beyond the eye. Its caudal fin is square-shaped with few to no dark spots.
Salmo trutta is recorded around the coasts of the British Isles.
Salmo trutta is cosmopolitan and recorded in Europe, Asia, Australasia, Africa and the Americas.
The brown trout is found in streams, ponds, rivers, lakes and saline coastal waters. Anadromous populations, commonly referred to as sea trout, spend their adult life at sea in coastal areas and return to freshwater to spawn in Autumn. The freshwater juveniles then undergo physiological changes as they migrate to salt water (smoltification).
Salmo trutta is native to Europe, North Africa and western Asia however, it is now distributed globally. Its expansion is thought to be a result of fish stocking programmes that were encouraged due to its economic and recreational value in the angling community (Burrill, 2014). As a result, Salmo trutta is considered an invasive species with major threats in the United States and New Zealand. For instance, brown trout are vectors for parasites, have displaced native fish species and have altered primary and secondary production rates (Jones & Closs, 2017; Budy & Gaeta, 2017).Its global success has been attributed to its phenotypic plasticity and capability to withstand environmental disturbances. For example, research suggests when Salmo trutta is reared in high levels of water velocity it can cause morphological changes to make it more streamlined. This change in the body is not seen when Salmo trutta is reared in low water velocity (Pakkasmaa & Piironen, 2000). This indicated that Salmo trutta had an adaptive response early in life that may be beneficial for the survival of the species in the future (Sommer, 2020).
Adam, P., James, C. & Speas, C., 2008. Brown trout (Salmo trutta) Species and Conservation Assessment. Grand Mesa, Uncompahgre and Gunnison National Forests.
Freyhof, J. 2011. Salmo trutta. The IUCN Red List of Threatened Species 2011: e.T19861A9050312. https://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T19861A9050312.en. Downloaded on 09 February 2021.
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Last Updated: 16/02/2021