trout species


SEA TROUT [Salmo trutta.]

Sea Trout were originally a European species but have been introduced to environments all over the world to the extent that they are now considered to be a worldwide species. A migratory (anadromous) species, there is no genetic difference between Sea Trout and the freshwater Brown Trout – they are the same fish. The difference comes from the fact that all trout hatch in freshwater. Some trout migrate to the sea and may live there for years (being classed as ‘Sea Trout’). Trout found in the sea are almost certain to be female. After a while they will return to up rivers to freshwater to find the males and reproduce.


Sea Trout are easily distinguished from Brown Trout by their silvery bodies with small black spots. They have a straight-edged caudal fin and after they have been in the river for some weeks, or even months, before spawning, they become darker and blacker or redder.


Sea Trout are found in all rivers which are fast flowing and clean enough for them to breed and migrate. In the seas, Sea Trout don’t make the same long journeys as salmon but stay within a general area (up to 125 miles) of their home river. Young Sea Trout have been found to be guided back to their natal  stream by scent, but older fish are guided back by sight and experience. Even if they are captured and released outside their home range, will be unable to find their way back.


Sexually mature when three to four years old, they generally begin their upstream migration in summer and spawn in the upper reaches of rivers and streams from October to January. They excavate nests in the river bed in a similar way to the Brown Trout. The fry and the parr develop in fresh water and then from about two years old make their way gradually down to the sea. They remain inshore for between one and three years, feeding and growing, and after attaining sexual maturity they migrate upstream again back to their spawning grounds.

Part of the migrating population (chiefly the males) dies after each spawning, largely as a result of exhaustion, since the fish do not feed while migrating.


During their stay in the sea they feed on sand eels, sprats, other small fish and crustaceans. There has been some controversy as to whether or not Sea Trout feed in the rivers on the way up to their spawning grounds. There is little doubt that they do, however, in many cases not enough, as they continue to lose weight until spawning, as do salmon.


A Guide: Freshwater Fish of Britain, Ireland and Europe

Trout Unlimited Stream Explorers
Canal & River Trust
British Trout Association
The Wild Trout Trust

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