You've probably heard that oily fish are a rich source of Omega-3. But you may be surprised to hear that fish don't actually make Omega-3 themselves... just like us, they get it from the food they eat. That food is marine algae.
Algae is the original manufacturer of Omega-3 in the sea. This algae is then eaten by small organisms such as plankton and krill, which in turn are 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!