TROUT (Salmo trutta), a fish closely related to the salmon, but with a larger mouth, the maxillary extending to below the posterior edge of the eye in fish 6 in. long well beyond the eye in larger ones, and with the caudal fin less emarginate. In the sea the trout ranges from Iceland and northern Europe to the Bay of Biscay, but as a fresh-water fish occurs in the countries north of the Mediterranean eastwards to Greece, and in Corsica, Sar dinia and Algeria : a trout from the mountains of south-east Morocco has been described by Pellegrin as Salmo pallaryii (Bull. Mus., Paris 1922). The trout of the Black, Caspian and Aral seas and their tributaries have smaller scales. The sea trout is silvery, with X-shaped blackish spots; it ascends rivers to breed and forms fresh-water colonies in every river and lake that it enters; the presence of trout in the Mediterranean coun tries indicates that in glacial times sea-trout frequented the Mediterranean. The river and lake trout show great differences in size and coloration and many specific names have been given; but it seems clear that all are but varieties of the one main species. In large lakes a weight of so lb. may be attained, whereas
in some small mountain streams a fish of 4 oz. is exceptional ; the coloration varies from silvery white to blackish, with spots that may be few or many, stellate or rounded, black, brown or red.
In eastern North America the name trout is given to a char (Salvelinus fontinalis) and in the west this name is given to the steelhead (S. gairdneri) of the Pacific coast and its numerous fresh-water derivatives, which exhibit just as much diversity in coloration as the trout of Europe and have received even more specific names; the best known is the rainbow trout (S. irideus). These trout of the Pacific slope have the caudal fin spotted, and often a red band along the side of the body; their relationship to the trout of Europe is not very close, their nearest allies being the various other Pacific species of Salmo, which are generally termed salmon.