Composition of fish oils
Fish oils are liquid at room temperature but generally solidify below 158–108C. Their composition is dependent on the type of fish. Most of the inedible fish are pelagic – that is, swim and shoal in the upper layers of the sea. These species generally store oil in the body rather than the liver. The species caught in Amer- ica – South (Peru and Chile) and North (USA) have a high content of LC omega-3 fatty acids which can be up to 35% of the total fat
in the fish. They are mainly eicosapentaenoic and decosahexae- noic acids (EPA and DHA) with some decosapentaenoic acid (DPA) at around 10%. The European fish species such as capelin, herring, sand eel and sprat are intermediate, have between 18% and 25% LC omega-3 fatty acids (Table 1). The demersal fish store oil in the liver, e. g. cod and halibut and have a low content of LC omega-3s (15% to 20%). The more unsaturated fish oils with a higher content of LC omega-3 fatty acids also have a higher con- tent of saturated fatty acids such as myristic and palmitic. The unsaturated oils are susceptible to oxidation. For storage, all fish oils have to be out of contact with air, pro-oxidant metals, espe- cially those high in iron and copper, and preferably treated with an antioxidant, such as butylated hydroxy-toluene (BHT).