Lipids in female northern bluefin tuna (Thunnus thynnus thynnus L.) during sexual maturation

Total lipids, lipid classes, fatty acids and vitamin E contents were measured in ovary, liver, dark muscle, white muscle and mesenteric perigonadal fat in four maturational stages of Atlantic female northern buefin tuna (Thunnus thynnus thynnus L.) during migration to Mediterranean spawning grounds through the Strait of Gibraltar. Ovary lipid content increased significantly by 37.6-fold from inmature to spawning stage, accumulating large quantities of steryl/wax esters, whereas the ratio of mesenteric perigonadal fat (primarily triacylglycerols) weight to ovary weight decreased linearly throughout maturation. In contrast, liver, dark red and white muscles lipid content did not show a major depletion during maturation compared to that of perigonadal fat. The fatty acid composition of ovary from bluefin tuna showed that docosahexaenoic acid (DHA; 22:6n-3) was the most abundant fatty acid and DHA: EPA: AA and DHA: EPA ratios were 19.3/4.3/1 and 4.5/1, respectively. Neutral lipids predominated over polar lipids (2-3:1) in ovary and triacylglycerol and steryl/wax ester were major lipid classes. In general, fatty acid composition of most tissues examined were similar to each other but, in contrast, the fatty acid profile of perigonadal fat was rich in monoenes such as 18:1n-9, 20:1n-9 and 22:1n-11, and DHA decreased significantly at spawning stage. The total lipid balance suggested for the disappearance of lipid from perigonadal fat depots and, to a lesser degree, from muscle and liver depots, reflected lipid utilization for gonadal development on the one hand and non-gonadal metabolism in the other. The former included lipid transferred to the gonad and lipid catabolized to provide metabolic energy for the biosynthesis of gonadal constituents and the later was likely to be lipid catabolism to provide energy for swimming during spawning migration.