Salmo trutta

The brown trout (Salmo trutta) is a species of carnivorous ray-finned fish and the most widely distributed species of the salmonid genus Salmo, endemic to most of Europe, West Asia and parts of North Africa, and has been widely introduced globally as a game fish, even becoming one of the world's worst invasive species outside of its native range.

Brown trout are highly adaptable and have evolved numerous ecotypes/subspecies. These include three main ecotypes: a riverine ecotype S. trutta morpha fario, commonly called river trout; a lacustrine ecotype S. trutta morpha lacustris, also called the lake trout (not to be confused with the lake trout in North America, which is a species of char); and an euryhaline ecotype S. trutta morpha trutta, also known as the sea trout. Sea trout in Ireland and Great Britain have many regional names: sewin in Wales, finnock in Scotland, peal in the West Country, mort in North West England, and white trout in Ireland.