They range from 15 mm to 21 m in length and from five gm. to 25 tons. Fishes may be found in all the shapes, man can think of. They are aquatic and found in fresh brackish waters. They have a very wide range of temperature tolerance and, therefore, may be found at poles as well as in hot springs.

The association of man with fish is as old as the history of man itself but its importance as food has increased many folds because of immense population growth and health hazards. Fish meat is cholesterol free and is good for health. It also reduces pressure on livestock by providing an alternate source of meat.