Dietary lipid composition affects blood leucocyte fatty acid compositions and plasma eicosanoid concentrations in European sea bass ( Dicentrarchus labrax)

Broodstock European sea bass were fed three dry pelleted feeds for 12 months prior to the onset of spawning. The diets contained (a) Northern hemisphere fish meal and oil (control), (b) krill meal and Northern hemisphere fish oil (krill), or (c) Northern hemisphere fish meal and tuna orbital oil (RoPUFA). The RoPUFA diet contained more docosahexaenoic acid (22:6 n−3; DHA) (60%), less eicosapentaenoic acid (20:5 n−3; EPA) (20%) and more arachidonic acid (20:4 n−6; AA) (two-fold) compared to the other two diets. The total lipid fatty acid composition of purified blood leucocytes broadly reflected the dietary fatty acid input, with respect to the three long-chain highly unsaturated fatty acids (HUFA) described above, although DHA levels were only slightly elevated in the fish fed RoPUFA. The fatty acid compositions of the major phospholipid classes of blood leucocytes, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI), were measured. In all phospholipid classes, the 22:6 n−3 level was relatively constant for all dietary treatments suggesting that dietary 22:6 n−3 concentrations were adequate in all diets. By contrast, the apparent demand for AA was not met by the control and krill diets while the moderately increased AA present in the RoPUFA diet was rapidly and efficiently incorporated into cellular lipids. The percentages of 20:4 n−6 varied in accordance with dietary input with highest levels in leucocytes from fish fed RoPUFA followed by those fed the krill diet and lowest values in control fish. Percentages of 20:5 n−3 were also influenced by diet with the highest levels found in fish fed the krill diet and the lowest in fish fed RoPUFA. Thromboxane B 2 (TXB 2) and TXB 3 derived from AA and EPA, respectively, were measured in plasma. In all dietary treatments, more TXB 2 than TXB 3 were produced with the highest values of the former found in fish fed RoPUFA. Leukotriene B 4 (LTB 4) and LTB 5 derived from AA and EPA, respectively, were also measured in plasma but no significant differences were found between dietary treatments.