text: Marine and freshwater fish oil vary in contents of arachidonic acid, EPA and DHA. The various species range from lean to fatty, and their oil content in the tissues has been shown to vary from 0.7% to 15.5%. They also differ in their effects on organ lipids. Studies have revealed that there is no relation between either 1) total fish intake or 2) estimated omega−3 fatty acid intake from all fish and serum omega−3 fatty acid concentrations. Only fatty fish intake, particularly salmonid, and estimated EPA + DHA intake from fatty fish has been observed to be significantly associated with increase in serum EPA + DHA.
  As of 2019, the US Food and Drug Administration (FDA) has approved four fish oil-based prescription drugs, namely Lovaza, Omtryg (both omega-3 acid ethyl esters), Vascepa (ethyl eicosapentaenoic acid), and Epanova (omega-3 carboxylic acids). None of these drugs are actually fish oil; they are all derivatives of acids found in fish oil.
  Uses
  Often marketed and sold for consumption as part of the diet or in dietary supplements in contemporary societies, fish oils also have found roles in external use, as emollients
  or as general ointments
  as well as in body art,
  or for alleged insulation against cold temperatures.
  Food sources
  The most widely available dietary source of EPA and DHA is cold-water oily fish, such as salmon, herring, mackerel, anchovies, and sardines. Oils from these fish have a profile of around seven times as much omega-3 oils as omega-6 oils. Other oily fish, such as tuna, also contain omega-3 in somewhat lesser amounts. Although fish is a dietary source of omega-3 oils, fish do not synthesize them; they obtain them from the algae (microalgae in particular) or plankton in their diets.