DEAL-FISH, the name applied to marine fishes of the genus Trachypterus, which, together with the oar-fish (q.v.), comprises the family Trachypteridae, or ribbon-fish. Deal-fish inhabit the middle waters, probably not below 200 fathoms, and are charac terized by their long, laterally compressed bodies, short head, narrow mouth and feeble dentition. The dorsal fin extends the length of the back, the anal is absent, and the caudal, when present, is reduced. The pectoral fins are small. In young deal fish some of the fin-rays are prolonged in an extraordinary way. Deal-fish may reach a length of eight feet. They have a world wide distribution. All the specimens found at the surface of the sea have been more or less mutilated by the release from the enormous pressure under which they are accustomed to live. The commonest species is T. arcticus.