Krill oil is extracted from Antarctic krill, Euphausia superba, a zooplankton crustacean rich in phospholipids carrying long chain omega-3 polyunsaturated fatty acids, mainly EPA and DHA. Krill oil also contains vitamins A and E and astaxanthin. Krill are at the bottom of the food chain and therefore are thought not to accumulate such high levels of toxins and heavy metals as other marine life higher up the food chain.
Krill oil has a unique composition being mostly made up of phospholipids rather than the triglycerides which are found in fish oils. The krill phospholipids are naturally rich in omega-3 fatty acids and antioxidants which is very different from the usual profile of fish oils. The association between phospholipids and long-chain omega-3 fatty acids seems to improve the absorption of these essential fatty acids, increasing bioavailability.