Bigger tuna carry more mercury.

Yes. Mercury accumulates in tuna over time, so older, larger fish have more. That means species like bluefin, bigeye, and to a lesser degree yellowfin are riskier than smaller ones like skipjack.

Skipjack is the small one you usually get in “light” canned tuna. It has the lowest mercury levels — safe to eat a few times a week. Albacore (“white” canned) is a bigger species, so it’s moderate — maybe once a week. Bluefin and bigeye? Those are your sushi-grade giants. They can have mercury levels high enough that you want to be careful how often you eat them.

Size matters within a species too. A 200-pound bluefin has more than a 100-pounder. But for practical shopping: stick to skipjack if you eat tuna often. Save the fancy stuff for occasional treats.

This is one of those rare cases where the cheaper option is also the safer one.