Fish get mercury from the water they live in. All types of fish contain some amount of mercury. Larger types of fish can have higher amounts of mercury because they prey on other fish that have mercury too. Sharks and swordfish are among the most common of these.

Why do swordfish have high levels of mercury?

Nearly all fish and shellfish contain traces of methylmercury. However, larger fish that have lived longer have the highest levels of methylmercury because they've had more time to accumulate it. These large fish (swordfish, shark, king mackerel and tilefish) pose the greatest risk.

How do swordfish get mercury?

Fish absorb methylmercury from their food and from water as it passes over their gills. ... Large predatory fish consume many smaller fish, accumulating methylmercury in their tissues. The older and larger the fish, the greater the potential for high mercury levels in their bodies.