Mercury & Fish Consumption

Recent research has shown that some species of fish contain amounts of mercury that are associated with health risks if consumed. Mercury from many sources enters water where it is taken up by bacteria and plankton. These are then eaten by small fish, which are in turn eaten by larger fish such as swordfish, shark, and large tuna. Very large fish have consumed more small fish, and have accumulated more mercury in their body. Provincial and regional public health agencies have released recommendations and advisories based on the current evidence of mercury levels in certain types of fish.

Children and women of childbearing age should limit their intake of fish species with moderate to high mercury levels by avoiding fresh, frozen, and white canned albacore tuna, shark, swordfish, halibut, king mackerel, grouper, marlin, and orange roughy. Light canned tuna may also contain a significant amount of mercury and consumption should be limited. Women of childbearing age may eat up to three cans per week of light canned tuna, however pregnant or breastfeeding women should only eat one can per week, and young children under four years of age may eat one can or two half can portions of light canned tuna per week.

Despite these advisories, there is evidence to suggest that eating fish provides cardiovascular health benefits. Fish are also an excellent source of omega-3 fatty acids, which are necessary for brain development and function. It is recommended that all people consume two servings of fish a week according to Canada’s Food Guide. Women of childbearing age, pregnant and breastfeeding women, and young children should choose types of fish that are low in mercury and high in omega-3 fatty acids. These types of fish include sardines, canned salmon, wild and farmed fresh salmon, mackerel, herring, perch, trout, bass, tilapia, pollock, scallops, and shrimp.

Refer to the Guide to Eating Ontario Sport Fish for specific recommendations on the safe consumption of fish from local waters.