Fish and fish by-products are the main natural source of omega-3 polyunsaturated fatty acids, especially\ud EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), both of them with a great importance in\ud the food and pharmaceutical industries. Comparing to conventional fish oil extraction processes such\ud as cold extraction, wet reduction or enzymatic extraction, supercritical fluid extraction with carbon dioxide\ud under moderate conditions (25 MPa and 313 K) may be useful for reducing fish oil oxidation, especially\ud when fish oil is rich in omega-3 such as salmon oil, and the amount of certain impurities, such\ud as some species of arsenic. Furthermore, taking profit of the advantages of supercritical carbon dioxide\ud as extractive solvent, a coupled extraction-fractionation process is proposed as a way to remove free fatty\ud acids and improve fish oil quality, alternatively to physical and chemical refining procedures.Ministry of Education\ud and Science (CTQ2005-07301), Junta de Castilla y León (GR 167)\ud and Pescanova S.A. (Spain