FISHERY BULLETIN: VOL. 73. NO. 4 



composition of the total lipids of the liver. The 

 significance of these observations is obscure but it 

 is probable that the liver is active in de novo 

 biosynthesis of 16:0 and 18:0 acids. If 18:0 is desat- 

 urated to 18:1a) 9, it could explain the higher level 

 of the latter in the liver triglyceride in terms of a 

 temporary storage function before distribution 

 elsewhere. The same role could result in the liver 

 triglyceride accumulating 22:5o)3 at an in- 

 termediate stage between 20:5<d3 and 22:6<i>3 for 

 either conversion or catabolism. The two Atlantic 

 sturgeon do not appear to have as much fat in the 

 liver as observed in other species or perhaps in 

 animals from other habitats. Zaitsev et al. (1969) 

 show 8-16^ oil in livers of other than Danube 

 sturgeon, and 8-20% in the latter. The liver of an A. 

 mikadoi taken at sea near Hokkaido yielded 52% 

 oil by boiling (Tsujimoto 1926) and Shimma and 

 Shimma (1968) report 38 and 51% lipid in livers of 

 two A. baeri. 



Among the unusual fatty acids observed in the 

 fat of fish B, special mention should be made of the 

 NMID (nonmethylene-interrupted dienes) [20:2] 

 and [22:2] (Ackman and Hooper 1973; Paradis and 

 Ackman 1975). In vertebrate lipids these 

 unusual fatty acids are apparently deposited in 

 parallel with 20:1 and 22:1. The generally lower 

 levels of the latter in the lipids of fish A resulted in 

 the NMID [20:2] and [22:2] being barely detectable 

 (<0.01%) and they are not included in Table 1. The 

 food of sturgeons on the Nova Scotian shelf is 

 probably basically bottom invertebrates (Scott 

 and Grossman 1973). Many of these organisms are 

 potential sources of these unusual acids (Ackman 

 and Hooper 1973; Watanabe and Ackman 1974; 

 Ackman et al. in press). These acids do not appear 

 to occur significantly in the oils from pelagic fish 

 and it can be assumed that their occurrence in the 

 sturgeon is a food web effect rather than a 

 peculiarity of the species. The absence of 16:lttll 

 and 18:1<d13 suggests that indigenous biosynthesis 

 is unlikely. 



The levels of isoprenoid acids in triglycerides of 

 fish B, especially 3,7,11, 15-tetramethylhexa- 

 decanoic acid (phytanic), are unusually high for 

 marine fish oils (Ackman and Hooper 1968), but 

 the exclusion of these acids from the biospecific 

 phospholipids of animals higher than molluscs has 

 been observed previously (Ackman et al. 1970; 

 Ackman and Eaton 1971; Ackman and Hooper 

 1973; Hooper et al. 1973). The properties of phy- 

 tanic acid resemble those of 18:0 and a possible 

 unusual low turnover rate for Cjg acids (see below) 



could explain the accumulation of phytanic acid. 

 On the other hand, the relatively lower levels of 

 4,8,12-trimethyltridecanoic acid and 2,6,10,14-tet- 

 ramethylpentadecanoic acid (pristanic) are not 

 easily reconciled with this explanation. Some gas- 

 liquid chromatographic evidence based on calcula- 

 tion of retention times indicated the presence of 

 the chain extension product of phytanic acid, 

 5,9,13,17-tetramethyloctadecanoic, and of 6,10,14- 

 trimethylpentadecanoic acid derived from 4,8,12- 

 trimethyltridecanoic acid (Maxwell et al. 1973). 

 However, these components were only present in 

 trace amounts >0.01% and identifications are 

 speculative. 



The importance of marine algae (the primary 

 source of phytol from which phytanic acid is 

 derived) in the diet of sturgeons is not known 

 (Scott and Grossman 1973). In freshwater, Atlan- 

 tic sturgeon do eat algae (Leim and Scott 1966). 

 The unusually high levels of 16:2(d4, 16:3<»4, and 

 16:4u)l, all of which are primarily algal in origin 

 (Ackman et al. 1968), indicate that plants provide a 

 significant proportion of dietary lipids. The ten- 

 tatively identified higher homologues 18:2<rt4, 

 18:3a)4, and 18:4o)l behaved as appropriate polyun- 

 saturated fatty acids on nitromethane enrichment 

 (Jangaard 1965) and on thin-layer chroma- 

 tography on silver nitrate impregnated silicic acid 

 (Morris 1966), and were eliminated (probably con- 

 verted to 18:0) on hydrogenation. The retention 

 times in gas-liquid chromatography were 

 appropriate to the proposed structure (Ackman et 

 al. 1974). All of these acids may be found in trace 

 amounts in many marine oils, but in both of the 

 sturgeon oils were of much greater importance 

 than usual. As far as we are aware, these acids 

 originate in marine and not freshwater plant 

 lipids. Their exclusion from the polar lipids in- 

 dicates that they are biochemically functional. It is 

 known that 16:4<i)l does not chain extend to 18:4a)l 

 in the rat (Klenk 1963) and the reason for the 

 apparent facile chain extensions in sturgeon could 

 be due to a steady intake of the unusual G igacids or 

 their Gjg homologues from primary plant lipids, or 

 from the fats of marine invertebrates feeding on 

 macrophytes or unicellular algae, or to a general 

 tendency of sturgeons to chain extend Gig acids to 

 a stable accumulation of Gjg acids. The latter pos- 

 sibility, suggested to explain the accumulation of 

 phytanic acid, is part of the larger question of 

 turnover rates for fatty acids in the marine stur- 

 geon and is linked in turn to the freshwater as- 

 pects of their lipid biochemistry. It is probable that 



842 



