288 MARINE PRODUCTS OF COMMERCE 



Female fish were found to be high in fat for a month or so before spawning and 

 very low in fat immediately after spawning. 



A consideration of their results and a comparison of the many published 

 analyses of fish make it plain that a single analysis, even if based on large num- 

 bers of individuals, cannot be accepted as representing a typical composition. 

 The great bulk of the proximate analyses of fish are therefore of httle value, 

 except that they may be used for the classification of fish into two general 

 groups: fatty and nonfatty (fish of low fat content). 



Clark and Almy have shown that the protein content is approximately the 

 same in both fatty and nonfatty fish. They conclude that "as the fat content in- 

 creases, the water content decreases, the protein remaining practically the same." 

 This relation is shown by their figures for blackfish, bluefish, Spanish mackerel, 

 and shad in Table 66. 



Source: Clark, E. D., and Almy, L. H., "A Chfemical Study of Frozen Fish in Storage 

 for Long and Short Periods," Ind. Eng. Chem., 12, 656-663 (1920). 



Table 67 by Manning (1935) presents the protein, fat, and vitamin content of 

 a number of fish and shellfish. 



Nature of Constituents 



Unfortunately relatively little work has been done to determine the exact 

 chemical nature of the organic substances forming the tissues of fish. It is mainly 

 the muscular tissue which serves as a foodstuff and therefore its composition will 

 be given the chief consideration in this chapter. The muscular tissue of fish con- 

 sists chiefly of water, proteins, and more or less fat. As the chemical nature of 

 fish fats is considered in some detail in the section on fish oils (Chapter 22), a 

 duplication of the discussion is vmnecessary. 



Nitrogenous Compounds 



The nitrogenous compounds occurring in fish muscle are for the most part 

 similar in nature to those found in the muscles of the higher vertebrates, except 

 that they contain more collagen and less extractives. 



Extractives. Various writers have shown that histidine, hypoxanthine, carnosine, 

 tyrosine, creatine, and creatinine are the principal organic compounds obtained 

 by aqueous extraction of fresh fish muscle. The presence of imidazo-ethylamine, 

 leucine, and alanine has also been reported. Okuda found the amounts of creatine 

 and creatinine in the aqueous extract of the fresh muscle of marine fish shown in 

 Table 68 (p. 289). 



