There has been a lot of discussion of Omega-3 fatty acids, DHA, EPA, etc. on this forum. I just wanted to share something I came across on Dr. John McDougall's website, which indicates one is not required to eat fish to obtain the benefits Omega-3 fats.

The text is fairly short on this page:
https://www.drmcdougall.com/misc/2009nl/sep/fav5.htm
and I will just paste some short excerpts here. You can search for "Vegetarians Make Plenty of Essential Fats (DHA)" to find the rest.

" "...it must be concluded that needs for omega-3 fatty acids can be met by dietary ALA (alpha linolenic acid)."1 ALA is made by plants."

"The human body has no difficulty converting the plant-derived omega-3 fat, ALA, into DHA or other omega-3 fatty acids, in the liver, thus supplying our needs even during gestation and infancy.2

With this solid science you can put your friends’ worries at ease—as a non-fish-eater you will be just fine. And you’ll also avoid all that toxic mercury and help restore our oceans."

There are references (1 & 2) for these statements.
Ron