Fish oils are the main dietary source of omega 3 essential fatty acids which contribute toward many biological functions in the human body The habitat in which the fish grow has a major influence on the amount of fatty acids they contain. Fish eat plankton which contain Omega 3. The colder the sea the higher the concentration of omega 3 the plankton will contain so oily cold water fish such as salmon tuna & mackerel have the highest levels of omega 3 & farmed fish contain lower levels.EPA