Mercury in Seafood

How does mercury get in fish?
Mercury is a naturally occurring metal, but it's also released into the environment via industrial pollution. Once rained or melted into the waterways, mercury is converted by bacteria into a more toxic form of the metal, methylmercury. As fish feed in these waters, they absorb the methylmercury. Most fish and shellfish have at least trace levels of it. And some fish—those that eat other fish, are larger, and live longer—have higher levels than others. These include swordfish, king mackerel, shark, some kinds of tuna and tilefish. The Chilean sea bass, which is often sold in restaurants, and big-eye tuna, which is sometimes used to make sushi, also test high in mercury. Fish and shellfish low in mercury include catfish, cod, crab, flounder/sole, grouper, haddock, herring, lobster, mahi-mahi, ocean perch, oysters, rainbow trout and farmed trout, salmon, sardines, scallops, shrimp, tilapia, and pollock. Cooking does not affect the mercury content of fish.