The ocean is an important source of food supply. All of the great groups of animal kingdom contribute to the food supply from the sea. Even though the marine animal kingdom comprises the invertebrates, fishes, reptiles, birds and mammals, by far the most important are the fishes.
Some of these live near the surface such as, mackerel and herring, tuna and anchovies. They belong to the pelagic class of fish. The basis for the existence of the pelagic animal life is the abundant plant life, the microscopic algae. Another type is called the demersal fish.
They are found on or near the sea bed of the continental shelves. They are found up to a depth of 200 meters. Demersal fish comprise cod, had lock, halibut which live in temperate regions. In the tropical waters are found group and snapper.
The third type is called anadromous fish which are migratory in character. This type of fish lives in the sea but swims in the fresh waters of the coastal rivers. Salmon is the most important species of this type. Remember that the open ocean is not an important source of food fish.