smelt, common name for a small, slender fish of the family Osmeridae, closely allied to the grayling of the family Salmonidae (salmon family). Most species are marine, but some ascend freshwater streams to spawn and others are landlocked in lakes. The American smelt (or icefish), Osmerus mordax, averages 10 in. (25 cm) in length and 1 lb (.45 kg) in weight. It is valued for its delicious, fragrant flesh, although its feeding habits are destructive and sometimes cannibalistic. The candlefish (or eulachon), a smelt found from Oregon to Alaska, is named for the fact that it is so fat at spawning time that when dried and strung on a wick it can be burned as a primitive candle. In Alaska and NE Asia are found the northwestern smelt (or rainbow herring) and the pond smelt. The top smelt, Atherinops affinis, and jack smelt are Pacific silversides of the family Atherinidae, which belong to a different order. The deep-sea smelts, family Bathylagidae, are closely related to the true smelts. Deep-sea and true smelts are classified in the phylum Chordata, subphylum Vertebrata, class Osteichthyes, order Clupeiformes, families Bathylagidae and Osmeridae, respectively.

Any of certain slender, silvery, carnivorous, food fishes (family Osmeridae) having a small fleshy fin. Smelts live in cold northern seas, and most species spawn a short distance upstream. The American smelt (Osmerus mordax), introduced from the Atlantic to the Great Lakes, is the largest smelt, about 15 in. (38 cm) long. The European smelt (O. eperlanus) is similar. Among Pacific species are the rainbow herring, capelin, and eulachon, or candlefish, which is so oily at spawning time that it can be dried and burned as a candle. Silversides (see grunion) and other unrelated fishes are sometimes called smelts.

Learn more about smelt with a free trial on Britannica.com.