Fish that are known to have high levels of mercury include king mackerel, marlin, orange roughy, shark, swordfish, tilefish, bigeye tuna, and some types of freshwater fish such as northern pike and bass. Mercury levels in fish are measured as parts per million (ppm), and larger, older fish that eat other fish tend to have higher mercury levels due to the process of bioaccumulation
. It is recommended that certain groups, such as pregnant women, nursing mothers, and young children, avoid consuming fish with high mercury levels to prevent health risks
