In the omega 6 family, we can't make it from scratch like ALA. The one in plants is called linoleic acid. These are very similar. Linoleic is an 18 carbon, two double bond molecule. And then that is made into a long chain omega 6 called arachidonic acid. That's sort of the cousin to EPA. They compete with each other and cell membranes.
Bill Harris, PhD is an internationally recognized expert on omega-3 fatty acids and fish oil. He has more than 300 publications relating to fatty acids, including omega-3s, in the medical literature.