188 U. S. BUREAU OF FISHERIES 



CHEMICAL COMPOSITION AND NUTRITIVE VALUE OF FISH PROTEINS 



As was discussed in last year's report, technologists in the College 

 Park laboratory began, during the latter part of 1935, a study of the 

 composition and nutritive value of proteins in some of the commercially 

 important species of fish and shellfish. This information has been 

 desired by welfare authorities, physicians, dietitians, and others inter- 

 ested in nutrition and health. Protein, which is the basis of all diets 

 of man and his domestic animals, is a very complex chemical com- 

 pound and varies in biological or nutritive value according to its 

 composition. To date our technologists have isolated and determined 

 the amounts of cystine, tryptophane, arginine, histidine, and lysine 

 in cod, haddock, sea herring, Boston mackerel, Spanish mackerel, 

 croaker, mullet, shad, red snapper, halibut, lake trout, oysters, crabs, 

 clams, and shrimp. In feeding experiments with laboratory animals, 

 it was found that fish proteins were at least 90 percent digestible. It 

 was also found that the proteins from fishery products were definitely 

 superior to both casein and beef in promoting growth in the experi- 

 mental animals, when feci in a diet in which the protein was a limiting 

 factor. 



The concentrates, extracted from the various species of fish and 

 shellfish mentioned above, constitute a highly nutritious and attractive 

 flour or meal which consists of about 95 percent protein and 3 percent 

 mineral constituents. As it is almost a pure protein, it should have 

 great possibilities as an ingredient of baby and invalid foods. Like- 

 wise, it should be well suited for making such bakery products as 

 cookies and crackers. These concentrates could be made on a com- 

 mercial scale from many species of fish, not now finding a ready sale, 

 as well as from the edible trimmings of our common market fishes. 



MINERAL CONSTITUENTS OF FISHERY PRODUCTS AND BYPRODUCTS 



As has been stated previously, the mineral constituents of foods 

 are being shown to be of increasing importance as the science of 

 nutrition progresses. About 34 mineral elements have been identified 

 in sea water, and nearly all of them have been found, in traces at least, 

 in aquatic products. Among the minerals which have been shown 

 to be of great importance in nutrition are calcium, phosphorus, 

 iodine, copper, iron, manganese, and magnesium. In general, fishery 

 products are excellent sources of these mineral constituents and 

 superior sources of some of them, such as iodine. In order to deter- 

 mine the relative standing of various fishery products in these minerals, 

 detailed analyses were made, during 1937, of the kinds and quantities 

 of these mineral constituents in cod, haddock, mackerel, salmon 

 (canned), shrimp, crab meat, and oysters. 



FISH MEAL IN ANIMAL FEEDING 



The Bureau's cooperative experiments with the Department of 

 Poultry Husbandry at Washington State College, Pullman, Wash., 

 were continued during the past year. This work has been concerned 

 largely with the vitamin content of fish meals. 



In earlier studies evidence was obtained indicating the practica- 

 bility of producing fish meals containing sufficient vitamin D to 



