Molecular speciation of fish sperm phospholipids: Large amounts of dipolyunsaturated phosphatidylserine

The molecular species compositions of the main diacyl phosphoglyceride classes and ether-linked subclasses from sperm of three species of fish, sea bass Dicentrarchus labrax, Atlantic salmon Salmo salar and Chinook salmon Onchorhynchus tsawytscha, were determined. The phospholipids from sperm were highly unsaturated, dipolyunsaturated fatty acid (diPUFA) molecular species comprised 64.6 to 71.8% of phosphatidylserine (PS), 10.1 to 17.4% of phosphatidylethanolamine (PE), and 3.3 to 10.1% of phosphatidylcholine (PC). In sea bass sperm, di22:6n-3 phospholipid was the predominant diPUFA molecular species, but in both salmon species 22:5n-3/22:6n-3 was also a major constituent of PS. Phospholipids containing 22:6n-3 dominated in sea bass sperm with 16:0/22:6n-3 as a major component of PC and PE, and 18:0/22:6n-3 of PE and PS in addition to di22:6n-3 in the latter two classes. In contrast, both salmon species contained much more 20:5n-3 and less 22:6n-3 so that saturated/20:5n-3 and monounsaturated/20:5n-3 molecular species were more abundant than the corresponding molecules containing 22:6n-3. Ether-linked lipids comprised 11.3-36.3% of choline and ethanolamine phosphoglycerides in each fish species. Molecular species containing 22:6n-3 were the major components of 1-O-alkyl-2-acyl-glycerophosphocholine, especially 16:0a/22:6n-3 in sea bass and 18:1a/22:6n-3 in the two salmon species, while in 1-O-alk-1'-enyl-2-acyl-glycerophosphoethanolamine, 1:6:0a/22:6n-3 was the major component in both salmon and 18:0a/22:6n-3 in sea bass with 18:1a/22:6n-3 abundant in all three species. In Atlantic salmon 1-O-alkyl-2-acylglycerophosphoethanolamine comprised 24.6% of ethanolamine glycerophospholipids which were predominantly 16:0a/22:6n-3 and 18:1a/22:6n-3. Phosphatidylinositol from sperm was dominated by stearoyl/C-20 PUFA molecular species, in sea bass overwhelmingly 18:0/20:4n-6, while in both salmon species 18:0/20:4n-6 and 18:0/20:5n-3 were equally abundant.