To make purified Omega-3 it requires high-quality starting material, namely fish. Not all fish are equal when it comes to Omega-3 fatty acids content. Some fish are short in Omega-3 fatty acids, just like some people are deficient in this essential fatty acid. Cold water, such as anchovies, salmon, herring, mackerel, and sardines all have high concentrations of Omega-3 fatty acids. Species that have comparatively low concentrations of Omega-3 fatty acids comprise red snapper, tuna, catfish, and mahi-mahi.
When fish are harvested specifically for getting omega 3 capsules and fish oil supplements, they are heated in kettles of water, during which time the oils of the fish float to the surface and are separated by the processing by-products.