Canned mackerel generally has mercury at levels near that of salmon.

King Mackerel is known to contain a lot of mercury, but that is a different species of Mackerel which is quite large (in general, larger predatory fish have greater concentrations of mercury).

As long as you are eating the tinned Mackerels, the kind which are small like sardines, I don't think you have significant mercury risk. Canned/tinned mackerel and sardines are considered some of the safest and most sustainable fish you can consume.

https://www.csu.edu/cerc/researchreports/documents/MercuryFa...

Thank you! I plan to buy some after work. I want to try to incorporate fish into my diet. Final question: raw or cooked? Does cooking deplete some of the good stuff inside?

Cooking usually changes some of the vitamin/nutrient content, but honestly if you like cooked fish, cook it. If you prefer sushi/sashimi, go for that. With diet try not to let perfection get in the way of obvious improvements. I could get way more nutrients by eating liver raw, but y'know, um no thanks.

King Mackerel is on the FDA's do not eat list due to mercury content; Atka and Atlantic are fine.

How does a person determine what kind of mackerel it is?

For example: https://www.amazon.com/Season-Skinless-Boneless-Fillets-Mack...

Close your eyes and pretend it is what it says on the tin. Any kind of processed fish, even if they aren't explicitly adulterating it with something else, is going to have a bunch of other stuff caught up in the nets that winds up in the can.

This advice applies to virtually all other foods as well, so...