Omega -3 fatty acids are classified by their degree of saturation and position of double bonds. The so called polyunsaturated (PUFAS) are essential fatty acids in that they must be provided for in the diet. Of these biologically the most important are EPA (Eicosapentaenoic acid) and DHA (Docosahexanoic acid). The souces of these are oily fish such as herring, hoki, tuna and mackerel.
Very limited amounts of DHA and EPA can be derived from ALA (alphalinolenic acid) although chemically ALA is classified as an Omega 3 fatty acid.Whilst fish is a source of EPA and DHA, phytoplankton which fish eat is thought to be the major ultimate source. Speirs Nutritionals emulsions contain EPA and DHA to varying degrees depending on the source of the fish oil used to make the emulsion.