COMPOSITION OF NATURAL FATS AND OILS 187 



forms may be only a reflection of a difference in food habits rather than of 

 alterations in fat metabolism. Other possible causes might be seasonal or 

 environmental variations. A comparison of the analytical data on the 

 zooplanktons and copepods is given in Table 3, and that for the fishes is in- 

 cluded in Tables 4 and 5. 



The salmon plays a unique role among the fishes, for which reason it is 

 included both in the fresh water and in the marine group. For their first 

 2 or 3 years of life, the salmon live in fresh water, where they are known as 

 "salmon parr." The body fat of these animals approaches the composition 

 of fresh-water forms more nearly at this time than at any other stage. 

 Thus, Ci4 unsaturated acids are present and the Cie unsaturated acids are 

 at the highest level, while the C22 unsaturated compounds are at the lowest 

 point in the life cycle. Just before the end of their fresh- water sojourn, 

 they become silvery and are referred to as "smolts." They swim down- 

 stream and out to sea, and then the body fat begins to change to that typi- 

 cal of marine fishes. After maturing, the adult fish feed heavily in the sea 

 and return to the rivers for spawning. By this time their body fat has be- 

 come typically marine, with a larger proportion of the longer chain un- 

 saturated acids. During the journey upstream, the fishes fast. A con- 

 siderable amount of fat is transferred from the body depots to the gonads. 

 After spawning, most male fishes perish in the river, but some females are 

 able to return to the sea. These so-called "kelts" have been shown to be 

 extremely emaciated. A body fat content as low as 0.3% has been re- 

 ported, in contrast to a level of 13 to 14% in salmon fresh from the sea. 

 For further details, the reader is referred to the extensive studies of Lo- 

 vern i^e.ies.ieg 



A number of other unique features characterize the fat deposits of fishes. 

 For example, the liver serves as the main depot for fat storage in many spe- 

 cies, contrasted with the minor part it plays in most terrestrial forms. In 

 the case of some of the Elasmobranch families and the Physeteridae (sperm 

 whales), glycerol is found not only in ester linkage with the fatty acids but 

 also at the same time in ether linkage with some of the higher alcohols such 

 as batyl, selachyl, and chimyl alcohols. (For a discussion of the chemistry 

 of these alcohols, see Chapter IV.) Such a possible mixed ether-ester tri- 

 glyceride might have the composition^^ shown in the accompanying 



Octadecenyl alcohol H2C-0CH2{CH2)7CH-.CH(CHj),CH3 



Oleic acid HC-0C0(CH2)7CH-CH(CHj)tCHs 



Gadoleic acid H2C-OCO(CH2)7CH'CH{CH8),CHs 



formula. The presence of these glyceryl ethers has been reported by the 



