grayling, common name for a brilliantly colored fish belonging to the genus Thymallus, of the family Salmonidae (salmon family), and closely allied to the smelt. Graylings are found chiefly in clear, cold, fresh waters of the Northern Hemisphere. They average 1 ft (30 cm) in length and 1 lb (.45 kg) in weight and exhibit hues of silver, gold, violet, blue, and olive brown. The American species include the arctic grayling, said to reach 4 lb (1.8 kg), the now scarce Michigan grayling, and the Montana grayling, found in the tributaries of the Missouri. The genus name, Thymallus, refers to the odor of wild thyme characteristic of the delicious flesh of fresh specimens. Graylings are classified in the phylum Chordata, subphylum Vertebrata, class Osteichthyes, order Clupeiformes, family Salmonidae.

Any of several game fishes (genus Thymallus), similar to trout, that are found in cold, clear streams of Eurasia and northern North America. Graylings are silvery purple and reach a length of about 16 in. (40 cm). They have relatively large scales, a small mouth with weak teeth, and a sail-like, brightly coloured dorsal fin. They feed primarily on insects and spawn in shallow water in the spring. Pollution of streams has reduced the numbers of this excellent food fish.

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