Brown trout (Salmo trutta)

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help



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.

Recorded distribution in Britain and Ireland

Salmo trutta is recorded around the coasts of the British Isles.

Global distribution

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).

Depth range

0-190 m

Identifying features

  • Brown, yellow or silver sides with a white belly.
  • Dark spots with light halos appear above and below the lateral line.
  • Few scales.
  • Upper maxilla extends beyond the eye
  • Square like caudal fin without a noticeable wrist.
  • Very few dark spots on caudal fin.

Additional information

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).


  1. Adam, P., James, C. & Speas, C., 2008. Brown trout (Salmo trutta) Species and Conservation Assessment. Grand Mesa, Uncompahgre and Gunnison National Forests.

  2. Freyhof, J. 2011. Salmo trutta. The IUCN Red List of Threatened Species 2011: e.T19861A9050312. Downloaded on 09 February 2021.

  3. Budy, P. & Gaeta, J.W., 2017. Brown Trout as an invader: A Synthesis of Problems and Perspectives in North America. In Lobón‐Cerviá, J. and Sanz, N. (eds.). Brown Trout: Biology, Ecology and Management, New Jersey, USA: John Wiley & Sons, Ltd., pp. 523-543.
  4. Budy, P., Thiede, G.P., Lobón-Cerviá, J., Fernandez, G.G., McHugh, P., McIntosh, A., Vøllestad, L.A., Becares, E. & Jellyman, P., 2013. Limitation and facilitation of one of the world's most invasive fish: an intercontinental comparison. Ecology, 94 (2), 356-367. DOI
  5. Burrill, A., 2014. Brown Trout; and their Ecological Impacts as an Invasive Species. In Invasive Species of the Pacific Northwest: University of Washington.
  6. Froese, R. & Pauly, D. (ed.), 2019. Species summary for Salmo trutta, sea trout. Available from:
  7. Jones, P. & Closs, G., 2017. The Introduction of Brown Trout to New Zealand and their Impact on Native Fish Communities. In Lobón‐Cerviá, J. and Sanz, N. (eds.). Brown Trout: Biology, Ecology and Management, New Jersey, USA: John Wiley & Sons, Ltd., pp. 545-567.
  8. Pakkasmaa, S. & Piironen, J., 2000. Water velocity shapes juvenile salmonids. Evolutionary Ecology, 14 (8), 721-730. DOI
  9. Sommer, R.J., 2020. Phenotypic Plasticity: From Theory and Genetics to Current and Future Challenges. Genetics, 215 (1), 1-13. DOI
  10. Thorstad, E.B., Todd, C.D., Uglem, I., Bjørn, P.A., Gargan, P.G., Vollset, K.W., Halttunen, E., Kålås, S., Berg, M. & Finstad, B., 2016. Marine life of the sea trout. Marine Biology, 163 (3). DOI
  11. Vandeputte, M. & Labbé, L., 2012. Cultured Aquatic Species Information Programme. Salmo trutta. Cultured Aquatic Species Information Programme. [on-line]. Rome, Italy: FAO Fisheries Division. 2021[cited 03 February]. Available from:
  12. Vehanen, T. & Huusko, A., 2011. Brown trout Salmo trutta express different morphometrics due to divergence in the rearing environment. Journal of Fish Biology, 79 (5), 1167-1181. DOI


  1. NBN (National Biodiversity Network) Atlas. Available from:

  2. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2024-05-28


This review can be cited as:

Nash, R.A., 2021. Salmo trutta Brown trout. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 28-05-2024]. Available from:

Last Updated: 16/02/2021