The fatty acid composition in tuna (Bonito, Euthynnus pelamis) caught at three different localities from tropics to temperate

The present paper describes the effect of habitat on the fatty acid composition of the lipid of bonito (Euthynnus pelamis), which was caught at three different localities, Philippine Sea (the tropical zone; seawater temperature at the fishing ground was 27.8 degrees C), East China Sea (the subtropical zone; seawater temperature was 29.7 degrees C), and the Pacific coast of Japan (the temperate zone; seawater temperature was 20.3 degrees C). The total lipids of various organs and stomach contents were extracted and their fatty acid composition analysed by gas chromatography (GC). Docosahexaenoic acid (DHA; 22: 6n-3) was the major unsaturated fatty acid in the lipid of all specimens examined from all localities. The mean DHA content accounted for more than 25% (mean +/- standard error: 26.0 +/- 0.6%) of the total fatty acids (TFA) in the lipids of all organs, a lipid profile markedly different from that of other fish species whose fatty acid composition is generally variable. Particularly, the mean DHA content of lipids in bonito caught in the northern sea-area sample (the temperate zone) was always high (28.4 + 0.7% TFA) in the lipid of every organ Because the DHA contents of lipids of the stomach contents fluctuated between 9.9 and 31.9% TFA, bonito did not simply incorporate the fatty acid profile of the lipids of its prey fishes, but selectively accumulated the DHA. Though the mean DHA content in the lipid of all bonito from the tropical to the temperate zone was markedly higher than other marine fish species such as sardines and herrings, there was a small difference between those in the northern (28.4 + 0.7% TFA) and southern samples (the subtropical and tropical samples, 24.7 +/- 0.8% TFA) (P < 0.05). It is suggested that the difference between them may be due to environmental effects, for example, the temperature of the seawater and the fatty acid composition of the lipids of prey organisms.