Total lipids of olive pomace (OP), olive pomace diet (OP diet), fish oil diet (FO diet) and fish filets of farmed gilthead sea bream (fish fed with FO diet and OP diet respectively) were extracted and separated into polar (TPL) and neutral (TNL) lipids. All samples were assessed for their in vitro activity against washed rabbit platelets aggregation induced by platelet activating factor (PAF) and they were further analyzed by electrospray-mass spectrometry. The high levels of palmitic (16:0), oleic (18:1 cis omega-9), linoleic (18:2 omega-6) and docosapentaenoic acid (DPA 22:5 omega-3) contained in both OP and FO diets are reflected to the gilthead sea breams fed with the individual diet respectively, while the gilthead sea bream fed with FO diet displays a decrease in DPA. All samples contained various glycerophospholipids species. Two PE species were identified in OP, OP diet and fish fed with OP diet and not in FO diet, while that might be an indication that these substances are likely to be the key polar phospholipids that have the ability to be in vitro PAF inhibitors, i.e. inhibit the formation of atherosclerotic plaques in blood arteries. (C) 2016 Elsevier Ltd. All rights reserved.