In addition to triglycerides, fatty acids esterified with such com- 

 pounds as chimyl, batyl, and selachyl alcohols are found in shark-liver 

 oils. These alcohols are ether esters formed from higher normal fatty 

 alcohols with one of the «C-hydroxyl groups of glycerol (Loveml95l). 



Baldwin and Parks (19U3) have reported on the low-temperature crys- 

 talization of glycerides and the occurrence of some of the 18- and 20- 

 carbon-atom acids in menhaden oil. The separation and characterization 

 of several highly unsaturated fatty acids in sardine oil have been de- 

 scribed by Toyama and Tsuchiya (1953 a, b, c, d and e) and Tutiya (19U0), 

 Toyama and Shimooka 0-953 b and 195U) have made ultraviolet absorption 

 measurements of conjugated acids obtained by alkali isomerization of highly 

 unsaturated acids from sardine oil. 



Many other investigations have been made of the composition of fats 

 in fish. Pathak and Ojha (1957) have compared the fat of two species of 

 Indian freshwater fish to that of some British fresh-water fish and of 

 the herring with regard to component fatty acids. A comparison was also 

 made of the lipids of an Arctic fish to those of the guppy (Wilber 19h9), 

 The naturally occurring eicosapentaenolc acids have been shown consider- 

 able interest. Their presence has been reported by Toyama and Tsuchiya 

 (1935 c and e), Tutdya (19U0), and Toyama and Shimooka (1953 a) in sardine 

 oil, Matsuda (19U2) in bonito oil, Baldwin and Parks (19l3) in menhaden 

 oil, Tsuchiya and Kato (1950) in herring oil, Tsuchiya and Okubo (1952) 

 in fish-liver oil, and Abu-Nasr and Holman (195U) in cod-liver oil. Whit- 

 cutt and Sutton (1956) have isolated and determined the structure of an 

 eicosapentaenolc acid from South Africa pilchard oil. These acids are not 

 restricted to lipids of fish, however, as their occurrence also has been 

 reported in ox-liver lipid (KLenk and Dreike 1955), ox-adrenal lipid (Herb 

 et al. 1951), and butter fat (Shorland and Johannesson 1951) • 



From the many studies of composition, it is apparent that all fats 

 of aquatic animals possess an exceptional variety of fatty acids, mainly 

 unsaturated. The question arises as to what extent the complex mixture 

 of fatty acids found in most fish is due to the ingestion of fat of that 

 type or to modifications of ingested fat by the fish itself. Fresh- 

 water animals possess one broad type of fat, which distinctly differs from 

 that of marine species (Hilditch and Lovern 1936 and Lovern 1937 and 

 19U2). The difference between these two types of fats in fish is shown 

 mainly in the frequency of distribution of the unsaturated fatty acids; 

 that is, there is a shift from relatively greater amounts of the un- 

 saturated acids of shorter chain length of 16 and 18 carbon atoms in 

 fresh-water species to larger amounts of the longer chain acids of 20 

 and 22 carbon atoms in marine fish. The total amount of 16-carbon- 

 atom acids is also found to be less in marine fish. This same pattern 

 in composition of fat is found in the fat of marine and of fresh-water 

 plankton crustaceans (Lovern 1935), which are the main food link between 

 the aquatic plant and animal kingdoms. It thus would seem that the na— 

 ture of the fat of fish is due almost exclusively to the ingestion of fat 

 of the same type. Further supporting evidence for this view are the re- 

 sults of feeding experiments with the fresh-water eel (Lovern 1938), 

 On a typically high-fat marine diet (herring), there was appreciable 

 modification of eel fat in the direction of the dietary fat, 



29 



