Omega-3 is not a single thing. There are three important acids, ALA, EPA, and DHA. The first can be found in some plant sources, I mostly get it from flax, soy, and kale.
The latter two are only found in fish, and for the vegetarians, algae. A few people have mentioned cod liver oil. I supplement with an algae oil, it contains the omega-3s and I believe avoids the worry of toxic metals.
The latter two are only found in fish, and for the vegetarians, algae. A few people have mentioned cod liver oil. I supplement with an algae oil, it contains the omega-3s and I believe avoids the worry of toxic metals.