About 14,400 species--or about three-fifths of all known fish--live in the ocean. These saltwater, or marine, fish live in an almost endless variety of ocean environments. Most of them are suited to a particular type of environment and cannot survive in one much different from that type. Water temperature is one of the chief factors in determining where a fish can live. Water temperatures at the surface range from freezing in polar regions to about 86 °F (30 °C) in the tropics.
Many saltwater species live where the water is always warm. The warmest parts of the ocean are the shallow tropical waters around coral reefs. More than a third of all known saltwater species live around coral reefs in the Indian and Pacific oceans. Many other species live around reefs in the West Indies. Coral reefs swarm with angelfish, butterflyfish, parrotfish, and thousands of other species with fantastic shapes and brilliant colors. Barracudas, groupers, moray eels, and sharks prowl the clear coral waters in search of prey.
Many kinds of fish also live in ocean waters that are neither very warm nor very cold. Such temperate waters occur north and south of the tropics. They make excellent fishing grounds, especially off the western coasts of continents. In these areas, nutrient-rich water comes up from the depths and supports the plankton that, in turn, supports enormous quantities of anchovies, herrings, sardines, and other food fish.
The cold waters of the Arctic and Antarctic oceans have fewer kinds of fish than do tropical and temperate waters. Arctic fish include bullheads, eelpouts, sculpins, skates, and a jellylike, scaleless fish called a sea snail. Fish of the Antarctic Ocean include the small, perchlike Antarctic cod, eelpouts, and the icefish, whose blood is nearly transparent rather than red.
This entire section is a direct quote taken from DiscoverySchool.com
John E. McCosker, "Fish," Discovery Channel School, original content provided by World Book Online, http://www.discoveryschool.com/homeworkhelp/worldbook/atozscience/f/ 198340.html, July 17, 2001.
Fish of coral reefs
Fish of coastal regions