Bony FishGrouper, sea horses and eels are a few examples of the more than 30,000 species of bony fish.
The skeletons of these animals (Class Osteichthyes) are composed of bone. All bony fish have gills, which are essential for breathing in most species. They also possess a swim bladder, which helps manage neutral balance so the fish neither sinks nor floats. These fish need not continuously swim to breathe.
Cartilaginous FishSharks, rays, skates and chimaera are cartilaginous fish.
The skeletons of these animals (Class Chondrichthyes) are composed of cartilage instead of bone. Their bodies are covered with dermal denticles, providing a smooth appearance. Depending on species, they will have 5-7 gills for breathing. Many must continuously swim to breathe.