THE FATTY-ACID COMPOSITION IN TUNA (BONITO, EUTHYNNUS-PELAMIS) CAUGHTAT 3 DIFFERENT LOCALITIES FROM TROPICS TO TEMPERATE

The present paper describes the effect of habitat on the fatty acid co mposition of the lipid of bonito (Euthynnus pelamis), which was caught at three different localities, Philippine Sea (the tropical zone; sea water temperature at the fishing ground was 27.8 degrees C), East Chin a Sea (the subtropical zone; seawater temperature was 29.7 degrees C), and the Pacific coast of Japan (the temperate zone; seawater temperat ure was 20.3 degrees C). The total lipids of various organs and stomac h contents were extracted and their fatty acid composition analysed by gas chromatography (GC). Docosahexaenoic acid (DHA; 22 : 6n-3) was th e 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 caugh t 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 cont ents 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. Thoug h 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 t hose in the northern (28.4 +/- 0.7% TFA) and southern samples (the sub tropical and tropical samples, 24.7 +/- 0.8% TFA) (P < 0.05). It is su ggested that the difference between them may be due to environmental e ffects, for example, the temperature of the seawater and the fatty aci d composition of the lipids of prey organisms.