What Women Should Know About Biomagnification in Seafood

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Tuna has always been a food that we are told not to eat often and during pregnancy some suggest it should be avoided completely. Tuna is checked for mercury content but these tests are random and there are products on the shelf that contain unsafe levels of mercury. This is why doctors now advise that we limit the amount of tuna we eat. Opinions vary widely with some suggesting no more than two servings a week while others suggest we limit our consumption to once a month. Tuna is commonly discussed regarding its mercury content because it is a commonly consumed food but in fact many different kinds of seafood pose a risk.

Precautions about eating certain seafood are usually related to pregnancy and fetal development, however everyone should be aware of the toxic potential of the foods we eat. Women should always be careful to avoid seafood containing higher levels of mercury during their reproductive life.

"The FSA...recommends you avoid eating shark, swordfish or marlin completely during pregnancy and until you stop breastfeeding... Although the mercury in these fish won't harm you, mercury can harm your baby's developing nervous system(http://www.babycenter.ca/pregnancy/ref/tunaexpert/)."

When choosing seafood It is important to think about the life cycle of different species and biomagnification.


Biomagnification, also known as bioamplification or biological magnification, is the increase in concentration of a substance...that occurs in a food chain

Lipid soluble (lipophilic) substances cannot be excreted in urine, a water-based medium, and so accumulate in fatty tissues of an organism if the organism lacks enzymes to degrade them. When eaten by another organism, fats are absorbed in the gut, carrying the substance, which then accumulates in the fats of the predator. Since at each level of the food chain there is a lot of energy loss, a predator must consume many prey, including all of their lipophilic substances(http://en.wikipedia.org/wiki/Biomagnification).

This is why longer-living and larger fish pose a greater health risk.

It is important to choose seafood that has a shorter life cycle because it has less opportunity for biomagnification to occur. Choose fish that are lower on the food chain because at each level the potential amount of mercury increases. You also want to make sure that you do not choose to eat fish and crustaceans that are detritivores. They feed off of the detritus found on the bottom of lakes, rivers, and oceans. They eat whatever detritus they come across including dead fish. Although they are low on the food chain, because they eat dead fish they are still at risk for biomagnification.

Safe seafood choices include "sea bass, sole, cod, haddock, and plaice"(http://www.babycenter.ca/pregnancy/nutrition/foodsafety/seafoodexpert/).

"The FDA advises that pregnant women, women who may become pregnant, nursing mothers, and young children should avoid eating shark, swordfish, king mackerel and tilefish [(commonly known as snapper)] due to high levels of mercury in these fish...You may eat up to 6 ounces (one average meal) of albacore tuna per week(http://www.obfocus.com/nutrition/Seafood.htm)."

  • Limit tuna steaks, halibut, orange roughy to one meal per month(http://www.obfocus.com/nutrition/Seafood.htm).

  • Limit cod, pollock, haddock, tuna (6ounce can) to one meal per week(http://www.obfocus.com/nutrition/Seafood.htm).

  • Limit salmon and shellfish to 2 to 3 meals per week(http://www.obfocus.com/nutrition/Seafood.htm).

Fish is a healthy and beneficial food choice because it contains essential fatty acids and is low in fat but we need to be careful in choosing the fish that we eat.