GRAYLING (Thymallus)  , fishes belonging to the family Salmonidae . The best known are the " poisson bleu " of the Canadian voyageurs, and the European species, Thymallus vulgaris (the Asch or Asche of Germany, ombre of France, and temola of Upper Italy) . This latter species is esteemed on account of its agreeable colours (especially of the dorsal fin), its well-flavoured flesh, and the sport it affords to anglers . The grayling differ from the genus Salmo in the smaller mouth with comparatively feeble dentition, in the larger scales, and especially in the much greater development of the dorsal fin, which contains 20 to 24 rays . These beautiful fishes, of which five or six species are known, inhabit the fresh waters of Europe, Siberia and the northern parts of North America . The European species, T. vulgaris or vexillifer, attains, though rarely, a length of 2 ft . The colours during life are remarkably changeable and iridescent; small dark spots are sometimes present on the body; the very high dorsal fin is beautifully marked with purplish bands and ocelli . In England and Scotland the grayling appears to have had originally a rather irregular distribution, but it has now been introduced into a great number of rivers; it is not found in Ireland . It is more generally distributed in Scandinavia and Russia, and the mountain streams of central Europe southwards to the Alpine water of Upper Italy . Specimens attaining to a weight of 4 lb are very scarce .