- any fish of the class Chondrichthyes, including the sharks, skates, and rays, having a skeleton composed entirely of cartilage
- Any of various fishes of the class Selachii (or Chondrichthyes), having a skeleton that is made of cartilage. Cartilaginous fishes breathe through gill slits, of which there are usually five, and their toothlike or platelike scales (called denticles) are made of dentine and enamel. Sharks, rays, skates, sawfish, and chimaeras are cartilaginous fishes. Compare bony fish jawless fish.