Fish oil from fatty fish contains higher amounts omega-3 fatty acids such as EPA and DHA, the 2 fish oils that provide health benefits. Flaxseed oil comes from the flax plant and contains both omega-3 and omega-6 fats. Flaxseed oil contains the plant derived omega-3 fatty acid alpha-linolenic acid (ALA), which can be converted to EPA & DHA but very inefficiently (8-20% of ALA to EPA; .5-9% to DHA). Therefore, ALA is not considered a good source of the 2 potentially beneficial fish oils EPA and DHA. The other problem with flaxseed oil is that it contains high amounts of omega-6 fatty acids (FA) which competes with the benefits of omega-3s, meaning omega-6 FA tend to increase harmful inflammation, while omega-3s tends to lower it. Unfortunately the typical American diet contains approximately 15-25 times more omega-6 FA than omega-3. Ideally, omega-3 intake should be 2-4 times HIGHER than omega-6 intake. Many scientists believe this unbalanced ratio to be a contributing factor to the rise in inflammatory disorders (cardiovascular disease, arthritis, etc.) in the US. With that said, flaxseed oil may have other unique health benefits when consumed in the correct quantities but if you are looking for the specific benefits, such as maintaining heart, brain, hearing and vision health attributed to omega-3s, stick with fish oil as the source.