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.