ABSTRACT
The outer skin or epidermis of a fish secretes a large amount of mucus which serves partly to reduce the frictional resistance of the water and partly as a barrier to parasites. There are about 20,000 different living species of fish in the world, but we will consider in this chapter only those of economic importance. They are found in the group of bony fishes such as the herring-like fish, cod group fish, mackerel family fish, and flat fish. The body of a bony fish is covered more or less completely by scales. The distribution and possible existence of the scales should be considered because the scales can give the same effect as a mirror. In several species of the tuna group, only the breast region has an armor of large scales, while the rest of the body and the tail are naked. Fish flesh has a relatively poor supply of blood and is usually white.
