You may have heard that oily fish are a rich source of Omega-3. However you may be surprised to hear that fish don't actually make Omega-3 themselves... they get it from the algae they eat.
Algae is the original manufacturer of Omega-3 in the sea, through the process of photosynthesis. This algae is then eaten by small organisms such as planton and krill, which in turn is eaten by fish - this is why fish and krill are rich in Omega-3. Recent technological advancements now allow us to extract the Omega-3 directly from the algae source, leaving the fish out of it altogether!