Fish with low mercury levels are safe to eat when pregnant. Fish such as salmon, anchovies, herring, trout, shrimp and catfish are a good source of protein, iron, zinc and omega-3 fatty acids, according to Mayo Clinic.
Omega-3 fatty acids in fish help promote brain development in a fetus. Fish that can be unsafe to eat include shark, swordfish, king mackerel and tilefish, according to WebMD. These fish can contain mercury, which damages the brain development of a fetus. The mercury levels in these fish are safe for adults but can accumulate in the adult bloodstream, which is why doctors recommend that women stop eating fish with high mercury levels if they are trying to become pregnant.