any of several deep-sea fishes, family Alepocephalidae (order Salmoniformes), found in almost all oceans at depths up to 5,500 m (17,800 feet) or more. Slickheads are dark, soft, and herringlike; species vary greatly in structure, and a few possess light-producing organs. Some common features of the family are absence of a swim bladder, presence of a lateral line, and position of the dorsal fin far back and above the anal fin.