Salmo trutta 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Actinopterygii Salmoniformes Salmonidae

Scientific Name: Salmo trutta Linnaeus, 1758
Common Name(s):
English Brown Trout, Sea Trout
Taxonomic Notes: Genetic data indicate that S. trutta and some populations of hybrid origin are native in some rivers draining to the Mediterranean, the Black Sea (at least in upper Danube drainage) and the Caspian Sea (at least in upper Volga drainage). The present published data do not always enable to identify the head water populations of the different species on the basis of morphological characters (they may be distinguishable, but this simply has not been investigated).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2011
Date Assessed: 2010-03-05
Assessor(s): Freyhof, J.
Reviewer(s): Kottelat, M. & Smith, K.
Contributor(s): Kottelat, M.
A widespread species and overall Least Concern. However, anadromous part of populations (sea trout) and many lacustrine stocks have in many cases markedly declined because of pollution (and possibly from impacts from salmon farming). The phylogeographic structure is almost destroyed by stocking.

European Union 27 = LC. Same rationale as above.

Previously published Red List assessments:

Geographic Range [top]

Range Description:Atlantic, North, White and Baltic Sea basins, from Spain to Chosha Bay (Russia). Present in Iceland and in northernmost rivers of Great Britain and Scandinavia. In Rhône drainage, native only to Lake Geneva basin, which it entered after last glaciation. Native to upper Danube and Volga drainages. Introduced throughout Europe, North and South America, southern and montane eastern Africa, Pakistan, India, Nepal, Japan, New Zealand and Australia.
Countries occurrence:
Andorra; Austria; Belarus; Belgium; Croatia; Czech Republic; Denmark; Estonia; Faroe Islands; Finland; France; Germany; Guernsey; Hungary; Iceland; Ireland; Isle of Man; Jersey; Latvia; Liechtenstein; Lithuania; Luxembourg; Netherlands; Norway; Poland; Portugal; Romania; Russian Federation; Serbia; Slovakia; Slovenia; Spain; Sweden; Switzerland; Ukraine; United Kingdom
Additional data:
Range Map:Click here to open the map viewer and explore range.

Population [top]

Current Population Trend:Unknown
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:Habitat:
Cold streams, rivers and lakes. Spawns in rivers and streams with swift water. Lacustrine populations migrate to tributaries and lake outlets, rarely spawning on stone, wave-washed lake shores. Spawning sites usually characterised by downward movement of water into gravel. Sea and lake trouts forage in pelagic and littoral habitats, sea trouts mostly close to coast, not very far from estuary of natal river.

Anadromous, lacustrine and resident ecotypes. Spawns in couples between late October and March, usually in November-December. Females select spawning sites and deposit the redd. Males guard and defend females against other males. Eggs are covered with gravel by female. Both sexes usually survive spawning and anadromous trout migrate back to sea or lake in autumn or overwinter in rivers and migrate in spring (5-70 % repetitive spawners in Norway). Sea trouts generally feed in freshwater. Eggs are covered with 3-30 cm of gravel. Redd depth is positively related to female's size. Eggs in deep redds are less vulnerable to spates and wash-outs and more vulnerable to low oxygen concentrations and pollution. Fry usually emerge from gravel between March (Spain) and July (Finland). Parrs and resident trouts are territorial, feeding on drifting and benthic invertebrates. Success in finding and defending a feeding territory is positively correlated to size of fry and to mother's size. Being large is clearly advantageous at this stage of life cycle. Resident trouts usually spawn for the first time at 2-3 years and spawn 2-3 seasons. Smoltification usually complete at 2-3 years and 120-220 mm SL, but up to seven year old smolts are reported. Mean smolt age increases with latitude. All juveniles seem to have the genetic ability to smoltify and migrate; in some small, summer-dry streams all migrate. In other streams, almost none seem to migrate. Factors triggering the 'decision' of an individual to smoltify or not are not well understood. If migration is impossible, smolts may interrupt migration and become resident again. In most rivers, a greater proportion of females than males seems to migrate, apparently a response to a greater need for reproductive energy. Therefore, sex ratio is usually skewed towards females in smolts. Large anadromous females may spawn with small resident males (the reverse is not reported but is expected to be possible, too). Smolts start to migrate downstream in April-May when temperature increases from low winter level, reaching beyond 5-11°C; migration peaks at rising water levels with increased turbidity.

There is a great variability in life history details of lacustrine populations. In some lakes, fry may migrate to the lake and at least males may spawn for the first time at two years. In other lakes, parrs smoltify after spending 1-3 years in spawning streams and males feed 4-6, females 5-8 years before first reproduction. At sea and in lakes, trouts feed on small fish and large crustaceans. In lakes, aquatic and terrestrial insects may form an important part of the diet. After at least 18 month at sea, sea trouts start to return to rivers to spawn. The pattern and timing of upstream migrations depends on particular river, sex and age. Homing accuracy is not as high as in S. salar. After spending one summer at sea, whitling start to migrate in July-September to lower reaches of rivers to overwinter or mature and migrate to spawning sites. Anadromous adults migrate in May and enter rivers until late October. Most maturing whitlings are males and the proportion of whitlings might be up to 30 % among spawners. Whitlings usually sneak in to spawn in redds of large couples, as resident males do, too. Large males attack, injure and often kill sneakers. After one spawning season as whitling or resident male, individual trouts may spawn again as large sea trout. The factors triggering the 'choice' to reproduce as whitling or as large male seems to be related to body size of young parrs since larger parrs more frequently develop the whitling tactic and smaller parrs the large male tactic. During upriver migrations, the silvery colour evolves into a dark breeding colour, the skull of males enlarges and the lower jaw develops a kype. Sometimes hybridises with S. salar.
Movement patterns:Full Migrant

Use and Trade [top]

Use and Trade: It is harvested for human consumption, and for sport fishing.

Threats [top]

Major Threat(s): Locally threatened by water pollution and impacts from salmon farming (sea lice etc.)

Conservation Actions [top]

Conservation Actions: No information available.

Classifications [top]

5. Wetlands (inland) -> 5.1. Wetlands (inland) - Permanent Rivers/Streams/Creeks (includes waterfalls)
suitability:Suitable  major importance:Yes
5. Wetlands (inland) -> 5.5. Wetlands (inland) - Permanent Freshwater Lakes (over 8ha)
9. Marine Neritic -> 9.1. Marine Neritic - Pelagic
9. Marine Neritic -> 9.10. Marine Neritic - Estuaries

In-Place Research, Monitoring and Planning
In-Place Land/Water Protection and Management
In-Place Species Management
In-Place Education
8. Invasive and other problematic species, genes & diseases -> 8.1. Invasive non-native/alien species/diseases -> 8.1.1. Unspecified species
♦ timing:Ongoing    
→ Stresses
  • 2. Species Stresses -> 2.1. Species mortality

♦  Food - human
 Local : ✓   National : ✓ 

♦  Sport hunting/specimen collecting
 National : ✓  International : ✓ 

Bibliography [top]

Bernatchez, L. 2001. The evolutionary history of brown trout (Salmo trutta L.) inferred from phylogeographic, nested clade, and mismatch analyses of mitochondrial DNA variation..

Elliot, J.M. 1994. Quantitative ecology and the brown trout. Oxford University Press, Oxford.

IUCN. 2008. IUCN Red List of Threatened Species. Available at: (Accessed: 5 October 2008).

IUCN. 2011. IUCN Red List of Threatened Species (ver. 2011.1). Available at: (Accessed: 30 June 2017).

Klemetsen, A., Amundsen, P.-A., Dempson, J.B., Jonsson, B., Jonsson, N., O'Connell, M.F. and Mortensen, E. 2003. Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories.

Kottelat, M. and Freyhof, J. 2007. Handbook of European Freshwater Fishes. Publications Kottelat, Cornol, Switzerland.

Citation: Freyhof, J. 2011. Salmo trutta. The IUCN Red List of Threatened Species 2011: e.T19861A9050312. . Downloaded on 22 June 2018.
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