Three common characteristics of all bony fish are that they have a bone skeleton, externally fertilize their eggs and have bony platelike scales. Bony fish are also known as Osteichthyes, and cover a diverse group of fish of over 20,000 species.
A key characteristic of these fish is their skeleton made of bones as opposed to cartilage. Bony fish can be broken into two key groups: lobe-finned fish and ray-finned fish. They can be found in freshwater and saltwater. Osteichthyes have a smooth mucus that covers their overlapping scales. Cartilaginous fish, like sharks, have a smooth skin as opposed to scales.