Fish that are low in mercury include catfish, mullet, flounder and anchovies. Most fish contain some amount of mercury, but fish that are lower on the food chain are generally the ones which contain the amounts that are considered negligible by the U.S. Food and Drug Administration.
In addition to fish, there are also shellfish that contain low mercury levels as well, such as shrimp, scallops and oysters.
Mercury turns into methylmercury when it is introduced to water. Fish absorb the methylmercury from the surrounding water that they live in. However, larger carnivorous fish, such as swordfish and sharks, accumulate the most methylmercury. As these larger fish eat smaller ones, the concentration of methylmercury in their bodies increases much more rapidly than it otherwise would if the fish simply absorbed the methylmercury from the surrounding water.
Low mercury fish and shellfish can be eaten at a rate of 36 ounces per week for a person that weighs around 132 pounds. A child who weighs 44 pounds should be limited to 18 ounces per week of low-mercury seafood. Men and women who engage in amateur fishing can check with their state's health department for information pertaining to what species of fish are safe to eat in their area.