text: According to ConsumerLab.com tests, the concentrations of EPA and DHA in supplements can vary from between 8 and 80% fish oil content. The concentration depends on the source of the omega-3s, how the oil is processed, and the amounts of other ingredients included in the supplement. However, the bioavailability of EPA and DHA from both capsular and emulsified fish oils has been shown to be high. A ConsumerLab.com publication in 2010 stated that 3 of 24 fish oil supplements tested contained less EPA and/or DHA than was claimed on the label. A 2012 report stated that 4 of 35 fish oil supplements that were tested contained less EPA or DHA than was claimed on the label, and 3 of 35 contained more.
  Quality and concerns
  Problems of quality have been identified in periodic tests by independent researchers of marketed supplements containing fish oil and other marine oils. These problems may include contamination, inaccurate listing of EPA and DHA levels, spoilage, and formulation issues.
  Contamination
  A report by the Harvard Medical School studied five popular brands of fish oil, including Nordic Ultimate, Kirkland and CVS. They found that the brands had "negligible amounts of mercury, suggesting either that mercury is removed during the manufacturing of purified fish oil or that the fish sources used in these commercial preparations are relatively mercury-free".
  There appears to be little risk of contamination by microorganisms, proteins, lysophospholipids, cholesterol, and trans-fats.