cusk, (Brosme brosme), long-bodied food fish of the cod family, Gadidae, found along the ocean bottom in deep offshore waters on either side of the North Atlantic. The cusk is a small-scaled fish with a large mouth and a barbel on its chin. It has one dorsal and one anal fin, both long and both connected, though only at the base, to the rounded tail. The cusk may grow about 90 to 110 cm (3 to 3.5 feet) long. It varies from yellowish or brownish to a slaty colour and when young may be vertically barred with yellow.