Well, first of all, eating tuna is generally questionable. It's very bad ecologically since tuna are dying out.
When I was a teenager, I had 6 cans A DAY. Cheap protein.
However, a well known consumer protection organizatino here in Switzerland analyzed approximately a dozen diffrent canned tuna brands. They found that 75% of the tested brands did contain far too much mercury.
E.g., only half a can of Albacore-Tuna A WEEK contains 160% of the mercury the FDA states to be harmless.
I wouldn't eat tuna. If you do, do it either once a week or make sure you get a certified lab analysis of the tuna of your choice to find out how much ercury it contains.