Before scientists became aware of the toxic effects of mercury—it poisons the kidneys and nervous system—this seemingly magical metal was widely used in medicine, cosmetics, and industries like hatmaking. While mad hatters are a thing of the past, mercury exposure is now a serious and widespread health problem. Even small amounts of mercury can interfere with brain development, making exposure particularly risky for children younger than six and women in their childbearing years. The U.S. Environmental Protection Agency estimates—conservatively—that more than 75,000 babies are born each year with a greater risk of learning disabilities because of their mothers’ mercury exposure. NRDC puts that number as high as 265,000 newborns every year.
But enough of the scary stuff. Here are a few easy ways to minimize exposure. For most people, the level of mercury absorbed by eating fish and shellfish is not a health concern. Overall, fish and shellfish are healthy foods. They contain high-quality protein and other essential nutrients, low in saturated fat, and contain omega-3 fatty acids, a type of essential fatty acid. A balanced diet that includes fish and shellfish can contribute to heart and in children's growth and development. Nearly all fish and shellfish contain traces of mercury. But some contain higher levels. Eating large amounts of these fish and shellfish can result in high levels of mercury in the human body. In the fetus or young child, this can damage the brain and nerves (nervous system).
Do not eat (or very exceptionally) shark, swordfish, king mackerel and tilefish because the level of mercury they contain is very high. Do not eat more than 300-400 grams of these different fish and shellfish, eat fish with a lower mercury content like- light tuna, halibut, albacore, sea devil, sea bass ... The smaller fish such salmon, cod, tilapia, shrimp, sardines, anchovies, etc. ... You can eat almost limitless quantities.
In most cases, we can say that the bigger the fish is, the longer it lives and has the higher position in the food chain, the more in itself can accumulate higher levels of mercury. Thus becoming potentially "rich in mercury content".