Fish is one of the important protein foods. The term is usually applied to all kinds of water animals used for food. They may be classified as follows:

In the white-fleshed fish the fat is found principally in the liver. This is the only class usually considered in the cookery for the sick.

In the dark-fleshed fish the fat is found distributed throughout the body. A considerable amount of the protein of fish is in the form of gelatin. Fish is less rich in extractives, and hence less stimulating than meat.

Digestibility

The digestibility of scaly fish depends upon the quantity of fat present and the coarseness of the fiber.

The white-fleshed fish are less nutritious and stimulating than the dark-fleshed fish as they contain less fat and extractives and more water. They are consequently more easily digested. "With the exception of cod, white fish is useful for a convalescent diet, for those of sedentary habits, for children, and others for whom the stimulating extractives of meat are not desirable.

Oily fish should not be eaten by those of weak digestion or given to the sick. In some cases they may be served during advanced convalescence.

Salt fish is not as easily digested as fresh fish, as the fibers are apt to be hardened in the process of salting. Salt codfish is an exception, for if finely divided and served in an appetizing manner it is a valuable and inexpensive form of protein food. As a rule, dried, smoked or pickled fish should not be given to the sick.

By some persons, fish cannot be eaten without causing indigestion or biliousness. A complete diet of fish is said to cause an affection of the skin. The fat sometimes disagrees, causing acidity and eructations of the stomach.

Composition

In composition fish is similar to meat, containing proteins, extractives, fats, salts and water. As a rule, fish contains more water and less fat than meat, therefore it is more easily digested; and it is due to this, its easy digestibility, that white fish by some is considered a brain food, and not, as is popularly supposed, to the amount of phosphorus it contains; in fact, fish does not contain as much phosphorus as some meat. Fish contains less extractives than meat and it is due to this that people tire more quickly of it than of meat.

Lemon juice and vinegar are desirable condiments to serve with fish. The acid is a desirable neutralizing agency, as the juice of fish, especially shellfish, is of an alkaline nature.

Nutritive Value

The chief nutritive constituents of fish, as of meat, are their proteins and fats. Their energy value depends largely on the amount of fat they contain.