Pregnant women and women considering pregnancy should not eat shark, swordfish, king mackerel or tilefish because they could contain enough mercury to harm an unborn infant’s nervous system, according to an FDA advisory. Young children and nursing women also should
avoid those species of fish.

The problem with these particular species of fish is that they live for a long time, giving time for higher amounts of contaminants to accumulate in their tissues, according to the FDA. The FDA notes that pregnant women can safely eat 12 ounces of other types of cooked fish each week.

Bacteria in both fresh and salt water convert mercury into methylmercury, a neurotoxic chemical that can cause brain damage, memory loss, personality change, tremors, spontaneous abortion, and damage to a developing fetus. Fish absorb and ingest the mercury and methylmercury, and store it in their tissues. Mercury is naturally occuring, but half of the mercury in the environment comes from smokestack emissions, incinerators, and coal-fired power plants.

Overfishing and How to Eat Fish Without Depleting Stocks

“The most recent report of the National Marine Fisheries Service, the federal agency that oversees domestic fisheries management, says that 92 domestic fish stocks are overfished, meaning that they are below a prescribed threshold.” - The San Francisco Chronicle

If you are a seafood lover concerned about contributing to species being overfished, depleted, and suffering from habitat problems, this colorfully illustrated guide from the National Audubon Society will be a wonderful addition to your life.

This excellent article–Troubled Waters–from the San Francisco Chronicle offers eco-friendly choices, and links for more detailed information.