Fish is beyond compare as a source of many nutrients vital to the developing infant, some of which may actually enhance development of the nervous system in babies and young children. Widespread contamination of fish with toxic mercury, however, has cast a shadow over the nutritional benefits of fish. Exposure to mercury in the womb can cause learning deficits, delay the mental development of children, and cause other neurological problems. Mercury consumed by a pregnant woman through contaminated fish can cross her placenta to damage the brain of her baby.