EFFECT OF PREY FISH LIPIDS ON THE DOCOSAHEXAENOIC ACID CONTENT OF TOTAL FATTY-ACIDS IN THE LIPID OF THUNNUS ALBACARES YELLOWFIN TUNA

The fatty acid composition of the lipid of yellowfin tuna (Thunnus alb acares) caught in two different localities, Philippine Sea (a tropical zone) and the Pacific coast area of Japan (a temperate zone) is descr ibed. The total lipids of various organs (dorsal ordinary muscle, vent ral ordinary muscle, dark muscle, liver, heart, pyloric cecum, and orb ital region) and of the stomach contents were extracted, and the fatty acid comosition was analyzed by gas-liquid chromatography (GLC). Doco sahexaenoic acid (DHA; 22:6n-3) was the major unsaturated fatty acid i n the lipid of all organs in the specimens examined from both localiti es, the mean DHA content accounting for more than 25% (mean +/- S.D. o f 26.9 +/- 5.7%) of the total fatty acids. This value is markedly diff erent from the fatty acid profile of other fish species, because, in g eneral, the fatty acid composition of other species is variable and th e DHA content is less than 20% of total fatty acids. Although the mean DHA content of the total fatty acids in the lipid of yellowfin tuna c aught in the tropical and temperate zones was markedly higher than tha t in other fish species, there was a small difference between that in the northern samples (temperate waters, 30.5 +/- 6.1%) and the souther n samples (tropical waters, 25.9 +/- 5.2%). It is suggested that this difference may be due to environmental effects, e.g., the fatty acid c omposition of the lipids of prey organisms, because there is also a sm all difference between the mean DHA content of northern prey fish (22. 7 +/- 6.1%) and that of southern prey fish (19.2 +/- 4.0%).