People who eat fish need clearer advice that balances the nutritional benefits, mercury contamination risks and ecological and economic effects of seafood, a review suggests. 

The team aimed to answer "which fish should I eat?" in a paper published in Friday’s issue of Environmental Health Perspectives.

Consumers get contradictory advice from different perspectives, Dr. Susan Korrick and Dr. Emily Oken of Brigham and Women's Hospital in Boston said.

"Our research shows that there is no one perfect fish when considering nutritional value, toxicity rates and the environmental and economic impact," Oken said in a release.

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Chum, coho, pink and wild Pacific salmon are listed by Toronto Public Health as safe to eat based on mercury contamination risk. (Frank Gunn/Canadian Press)

"Consumers are forced to decide what tradeoffs they are willing to make. But as a consumer standing in a store, it is difficult to understand the pros and cons of a fish purchase, because the amount of readily available information is limited."

Farm-raised salmon is high in heart-healthy omega-3 fatty acids and very low in mercury, a neurotoxin of concern for pregnant women and young children.

But some environmental groups list it as a "fish to avoid" on the grounds aquaculture may harm the integrity of ecosystem and wild fish stocks.  Farmed salmon may also have relatively high levels of PCBs, the authors said.

Economic viability of the fishing industry depends on having enough fish stocks and nutritional recommendations to increase fish consumption will only be met if the food source exists.

Variety in seafood diet

"We should continue to urge international organizations, governments and their agencies to promote remediation and, where possible, elimination of sources of fish contamination, and establish policies that promote environmentally responsible and economically viable fishing practices so fish can remain a part of a healthy human diet for future generations," the study's authors concluded.

In Canada, public health officials provide guidelines to encourage people to eat a variety of fish safely with the environment in mind.

Toronto Public Health's chart lists canned salmon and tilapia as safe to eat every day and breaks out servings for children and women who are pregnant or could become pregnant.

"Safe to eat sometimes" varieties based on mercury levels include catfish, kingfish, trout, snapper and canned white albacore tuna.

Tuna steak, marlin and pickerel are red listed as species to avoid or eat rarely.

For a given species, location matters. Shrimp can vary in their ecological rating depend on origin and the same holds true for higher methylmercury contamination when tilefish are caught in the Gulf of Mexico compared with the Atlantic Ocean, the U.S. researchers said.

Canadian studies have found higher levels of methylmercury exposure among those with higher fish consumption, such as anglers fishing in the Great Lakes, some Chinese-Canadian children and Arctic residents.

The U.S. study was funded by a Dartmouth College Superfund Research Program Grant, a Dartmouth Formative Children's Center Grant, the National Institutes of Health, the Harvard Clinical Nutrition Research Center, the Gelfond Fund for Mercury Research & Outreach, the Consortium for Interdisciplinary Environmental Research, SUNY Stony Brook, the Harvard Pilgrim Health Care Institute, the Swiss National Science Foundation, the National Institute of Environmental Health Sciences and the United States Environmental Protection Agency.