Sea trout is a close relative of the salmon, and is a migratory form of the common brown trout. They are originally from Europe where they live in lakes and then migrate to sea.
The sea trout is considered a delicacy in Europe, and are sometimes called a salmon trout. They are not the same as the American Sea trout. In mid-Atlantic States, the Weakfish is called a sea trout, but they are not closely related because it comes from the family Sciaenidae, and not the trouts family of Salmonidae.