FISHERY BULLETIN: VOL. 73, NO. 4 



the body fats of both sturgeon A and B. Therefore, 

 the pathway 16:l(o7»18:l<i)7->20:la)7 appears to be 

 important, suggesting a period of fatty acid 

 biosynthesis rather than of deposition of ex- 

 ogenous fatty acids. Both fish had about the same 

 percentages of 16:1. Fish A had higher proportions 

 of fat in the muscle than Fish B, and 18:lo)7 was 

 about a quarter of 18:lo)9 in this fat. In the leaner 

 fish B, 18:lo)7 was only about one-fifth of 18:la)9, 

 suggesting less activity in de novo biosynthesis. It 

 is possible that the diet of fish A was rich in the 

 polyunsaturated fatty acids, the deposition of 

 which was disturbing the typical species-fat com- 

 position. Accordingly, fish A may have been more 

 actively engaged in synthesizing monoethylenic 

 fatty acids, via 16:0>16:la)7*18:lo)7, to achieve this 

 composition. Seals, whose depot fat has a higher 

 iodine value than that of most whales, may show 

 the same monoethylenic fatty acid activity (Ack- 

 man, Epstein, and Eaton 1971). 



Earlier work on oils from four freshwater fish 

 showed l-37f 20:1 and about 0.3-0.4% 22:1 (Ackman 

 1967). Marine fish oils, in our experience, usually 

 show 109c or more of 20:1 and 5% or more of 22:1. 

 The absence of large proportions of 20:1 and 22:1 

 acids in the marine sturgeon depot fat, even in fish 

 B with the less unsaturated fat, is the key reason 

 for our placing the fat of the marine Atlantic 

 sturgeon in a rather special class of marine fat, or 

 more broadly, in the generally freshwater class of 

 fish fats, as recorded by Hilditch and Williams 

 (1964). 



ACKNOWLEDGMENTS 



J. Hingley assisted in the technical studies. P. J. 

 Ke gave valuable advice on oriental species and W. 

 J. Dyer on observations on the Atlantic sturgeon. 

 Personal communications from Y. Shimma and I. 

 Reichwald clarified anatomical problems. 



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