Expecting mothers and women trying to become pregnant should eat fatty fish at least once a week to foster brain development and prevent postpartum depression, U.S. health experts said Thursday, challenging guidelines that suggest seafood intake should be limited because of mercury contamination fears.

Salmon is high in omega-3 fatty acids and tends to be low in mercury contamination.

The National Healthy Mothers, Healthy Babies coalition — a nonprofit U.S. group that includes the American Academy of Pediatrics, the March of Dimes, the National Institute of Child Health and Human Development and the Centers for Disease Control and Prevention — said a recent survey showed that 90 per cent of women were eating less fish than the U.S. Food and Drug Administration recommends.

What types of fish are low in mercury?
Shellfish (oysters, clams, scallops, mussels), salmon, crab, shrimp, trout, herring, haddock, pollock (Boston bluefish), sole, flounder, lobster, Atlantic mackerel and lake whitefish.
Source: Health Canada

The U.S. coalition said that pregnant and breastfeeding women should eat a minimum of 12 ounces (340 grams) per week of fish like salmon, tuna, sardines and mackerel because they are a good source of omega-3 fatty acids, which aids with brain development.

"The group reviewed recent scientific studies and found a link between ocean fish consumption and advanced cognitive and motor skill development in children," coalition spokeswoman Dr. Ashley S. Roman, an assistant professor of obstetrics and gynecology at the New York University Medical Centre, said in a release.

"Some data also shows a connection with reduced pre-term labour and post-partum depression in mothers who ate ocean fish when pregnant."

The FDA in 2004 cautioned certain groups including women who are pregnant, breastfeeding or trying to become pregnant, against eating more than 12 ounces (340 grams) of certain kinds of fish including shrimp, canned light tuna, salmon, pollock and catfish per week over concerns regarding exposure to mercury. The FDA said exposure to trace levels of mercury could hinder brain development in unborn and young children.

Health Canada suggests pregnant women and breastfeeding mothers should eat no more than 5.3 ounces (150 grams) per month of certain types of predator fish including tuna, shark and escolar.

Mercury is a naturally occurring metal found in soil, rocks and water and is released in industrial emissions. Fish that feed on plants and organisms containing mercury build up mercury in their flesh and muscle tissue.