There are three types of omega 3 acids: alpha-linolenic acid (ALA) is from plant-based sources such as olive oil, walnuts and flax. Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are found only in fish, but small amounts can be converted from ALA in the body.
DHA is required in the brain for optimal memory and learning ability, as well as in the retina of the eye for visual acuity. EPA works primarily in the areas of mood and inflammation. In pregnant and lactating women omega-3 fats are especially important for the proper brain and eye development of the fetus and newborn.
You can get adequate amounts of all of these omega-3 fatty acids from flaxseed oil supplements and fish oil supplements.