Long lived predatory fish, such as mackerel, swordfish, shark, and tile fish are heavily contaminated with mercury and they should be avoided during pregnancy.
Fish contains protein, minerals, vital nutrients such as omega-3 fatty acids, and vitamins, which are essential for a developing baby and a healthy pregnancy. Fish also contain contaminants such as mercury, which is toxic and can impair a baby's developing brain and nervous system. Therefore, fishes with high quantities of mercury should be avoided during pregnancy. Large fishes that have long life spans, and are predatory (eat other fishes) tend to have higher amounts of mercury than small fishes. High-mercury fishes include mackerel, swordfish, shark, and tile fish.