They are native to the northern hemisphere. Trout have thick bodies and blunt heads, and vary in colour. Salmo trutta is widely distributed in Europe, occurring in British fresh and coastal waters.
Sea trout are generally silvery and river trout olive-brown, both with spotted fins and sides.
In the USA, the name 'trout' is given to various species, notably to the rainbow trout S. gairdneri , which has been naturalized in many other countries. Biologists in New Zealand identified in 1997 magnetite containing nerve cells in the nose of rainbow trout that are triggered in the presence of a magnetic field, thus aiding navigation.