The majority of fish in the world are classified as bony fish, including nearly all commercial and sport fishes. Bony fish are classified by their skeletons that are made, at least partially, of true bone rather than cartilage. Most bony fish also have a swim bladder, covered gill chambers, bony scales, external egg fertilization and a skull with sutures. Other fish, cartilaginous fish, have skeletons made from cartilage.
Bony fish inhabit waters all over the world. They come from shallow streams to deep seas, and from cold to warm temperatures. Their diet depends entirely on the species, but crustaceans, plankton, invertebrates and other fish are the most common prey.
Some species that are considered to be bony fish are tuna, Atlantic cod, marlin, sunfish, swordfish and seahorses. The first creatures that were similar to fish appeared over 500 million years ago, according to scientist and naturalist Jennifer Kennedy at About.com. Bony fish and cartilaginous fish separated approximately 420 million years ago.
The ocean sunfish is believed to be the largest out of all bony fish, reaching sizes of up to 11 feet and 5,000 pounds. The dwarf pygmy goby is considered the smallest, growing to roughly 1/3 of an inch.