When judged by its composition, the place of fish in the diet is the same as that of meat; that is, it is supplementary to cereals and other vegetables, most of which, as wheat, rye, maize, rice, potatoes, etc., are rich in carbohydrates, which are not present in appreciable amounts in the flesh of fish. Preserved fish, as a rule, show a small percentage of refuse, with the exception of a few kinds which are preserved whole. The percentage of actual nutrients is much larger than in the corresponding fresh fish, owing to the removal of a large part of the refuse and more or less water. The gain in nutrients is mostly represented by protein, which is the most valuable nutrient. Canned fish, which is in effect cooked fish, compares favorably as regards composition with the fresh material. Generally speaking, the amount of refuse is small, since the portions commonly rejected in preparation for the table have been removed before canning. Shellfish resemble meat and food fishes in general composition. They contain, however, an appreciable amount of carbohydrates. Judging by the relative amount consumed, oysters are the most important of the shellfish. Speaking roughly, a quart of oysters contains on an average about the same quantity of actual nutritive substances as a quart of milk, or three-fourths of a pound of beef, or two pounds of fresh codfish, or a pound of bread.
A number of experiments have been made with man to learn how thoroughly fish is digested and to compare it in this respect with other foods. It has been found that fish and lean beef are about equally digestible. In each case about 95 per cent. of the total dry matter, 97 per cent. of the protein, and about 95 per cent. of the fat were retained by the body. Other experiments of the same character indicate that salt fish is less thoroughly digested than fresh fish. The nutritive value of shellfish, as of other fish, depends to a considerable extent upon their digestibility; but so little is known upon this point that nothing more can be said with certainty here than that oysters belong to the more easily digestible class of foods. So far as can be learned no experiments have been made which show how thoroughly crabs, clams, and other crustacea, turtle and terrapin, and frogs' legs are digested. Inspection of a considerable number of dietary studies of families of farmers, mechanics, professional men, and others, carried on in different regions of the United States, shows that out of the 20 per cent. of the total food and the 43 per cent. of the total protein obtained from animal sources, only about 2 per cent. of the total food and 4 per cent. of the total protein is furnished by fish, shellfish, etc., showing to what a limited extent this valuable food is used in the average household. It is not improbable that in communities where fishing constitutes the principal industry much larger quantities are consumed. It has been found that the laborers employed in the fisheries of Russia consume from 20 to 62 ounces of fish daily. This, with some bread, millet meal, and tea, constitutes their diet throughout the fishing season. These quantities are unusually large, but no bad effects are mentioned as following the diet.
There is a widespread notion that fish contains large proportions of phosphorus, and on that account is particularly valuable as brain food. The percentages of phosphorus in specimens thus far analyzed are not larger than are found in the flesh of other animals used for food. But even so, there is no experimental evidence to warrant the assumption that fish is more valuable than meats or other food material for the nourishment of the brain. The opinion of eminent physiologists is that phosphorus is no more essential to the brain than nitrogen, potassium, or any other element which occurs in its tissues. The value commonly attributed to the phosphorus is based on a popular misconception of statements by one of the early writers on such topics. It should be stated that most physiologists regard fish as a particularly desirable food for persons of sedentary habits, since it is easily digested and not too hearty. While, so far as can be learned, such statements do not depend upon experimental evidence, they are thought to embody the result of experience.
In cooking, fish may be boiled, steamed, broiled, fried, baked, or combined with other materials in some made dish. When boiled, it is stated that the loss in weight ranges from 5 to 30 per cent., a loss that consists largely of water—that is, the cooked fish is less moist than the raw. Little fat or protein is lost. So far as known, experiments have not been made which show the losses l' other methods of cooking. It is, however, probable that there would be usually a very considerable loss of water.
In view of statements of a popular nature which have been made on the dangers from eating poisonous fish or from ptomaines contained in fish, a few words summarizing the actual knowledge on these topics seem desirable. There are several species of fish which are actually poisonous. Few of them, however, are found in the United States, and the chances of their being offered for sale are very small. Such fish are mostly confined to tropical waters. Fish may contain parasites, some of which are injurious to man. These are, however, destroyed by the thorough cooking to which fish is usually subjected. Occasionally cases of ptomaine poisoning have been traced to eating fish or fish products. Fish which has been frozen and, after thawing, kept for a time before it is cooked is especially likely to contain injurious ptomaines. Canned fish should never be allowed to remain long in the can after opening, but should be used at once. There is some possibility of danger from the combined action of the can contents and oxygen of the air upon the lead of the solder or the can itself. Furthermore, canned fish seems peculiarly suited to the growth of microorganisms when exposed to the air. Finally, fish offered for sale should be handled in a cleanly manner and stored and exposed for sale under hygienic conditions. Oysters when ‘floated’ or ‘fattened’ should never be placed in water contaminated by sewage. Severe illness and death have resulted in a number of cases from eating raw oysters contaminated with sewage containing typhoid fever germs.
For further information, consult the authorities referred to under Food; also Atwater, “The Chemical Composition and Nutritive Value of American Food Fishes and Invertebrates.” Report of Commissioner of Fish and Fisheries, 1883 (Washington, 1885); United States Department of Agriculture, Office of Experiment Stations,
