These fishes are strains of the same species. The sea trout adopts a lifestyle similar to salmon by migrating to sea to enjoy rich feeding and grow larger. The brown trout remains in freshwater throughout its life.
Some brown trout in the larger lochs change their feeding habits and prey on other fish, especially charr and this rich diet means that they may grow big, to over 20lbs. These record sized trout, known as ferrox, swim deep and are mostly caught by trolling.