They are native to Europe, western Asia, and the extreme northeastern edge of Africa and have been introduced to many waters suited to them around the globe. Although all brown trout are categorized as a single species, the fish themselves may show wide variation in color and spotting patterns, habitual foods, and behavior. Any angler who fishes a variety of rivers may eventually encounter brown trout that somehow look different from those he's used to catching and may even encounter two different-looking brown trout in the same stream. There are usually greater amounts of an overall yellow tint along the flanks.
Black spots are present on the back and in diminishing numbers down the sides.
Bright red spots are found in lesser numbers along the sides. There are few, if any, spots on the tail in contrast with rainbow, the tails of which are heavily spotted. Unlike brook trout, brown trout have no vermiculations, or wavy lines on their backs and have teeth along the full length of the vomerine bone on the roof of their mouths. Brown-trout coloration is much subdued in hatchery fish, but often assume the brighter colors of wild fish after several months in the stream. Brown trout are also unique in that they are able to change their color quite rapidly as a means of concealment.