What are some foods that contain omega 3 fatty acids?

Many: Fish is one of the most well known: such as salmon, tuna, sardines, and halibut; other seafood including algae and krill; some plants like brussels sprouts, kale, spinach, and salad greens ; flax seeds; and walnuts. Some people's systems are not efficient at converting alpha-linolenic acid (ala) from plant-based omega-3's to epa and dha that are needed; for these, fish or krill oil may be better.