FISH

FISH

 Fish account for more than half of all the vertebrate species known in the world, with more than 24.000 species identified so far. They are found in almos every watery habitat-salt, fresh, or brackish from large puddles to polar seas. They range in size from gobies, less than an inch long, to whale sharks, 59 feet long. Fish come in all colors and in thousands of patterns, but some are colored drably to blend in with their surroundings.Fish fall into three main groups: jaw less, cartilaginous, and bony. The category of jawless fish includes hag- fish and lampreys; the category of cartilaginous fish includes sharks and rays; and the category of bony fish, to which the largest number of fish belong, includes both the lobe-finned and the ray-finned fish species.

Most fish have scales that pro tect their bodies. Nearly all fish have fins, used for swimming. Flying fish can launch themselves into the air for brief periods, and some fish, such as walking catfish, use their fins to drag themselves along on land/

Most fish reproduce by means of eggs laid by the female and fertilizedby the male, outside the female's body. Many sharks, however, reproduce by internal fertilization and live birth from the mother's body.

Many fish eat algae or insect lar vae and other small animals, but some, such as sharks, are tireless predators that hunt even large sea mammals.

Fish frequently travel in large groups called schools or shoals. Using low-frequency sonar, researchers de tected a shoal of some 20 million fish.