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I am trying to eat more fish but I'm concerned about contaminants. Which are the best – and worst – types of fish to eat?


As a dietitian in private practice, I encourage my clients to include fish in their diet twice a week unless, of course, they're allergic or simply don't like its taste.

The key, though, is choosing the right fish to eat – fish that's packed with nutritional benefits and low in potentially harmful chemicals, and fish that are also farmed or fished in ways that don't take a toll on the environment. That's a lot to consider at the grocery store or restaurant.

Long list of health benefits

A regular intake of fish has been linked to a lower risk of a wide range of conditions, including high blood pressure, stroke, heart disease, type 2 diabetes, macular degeneration, rheumatoid arthritis, colorectal cancer and Alzheimer's disease.

Eating fish during pregnancy is also thought to help promote the development of a baby's brain and eyes.

The protective effects of fish are largely attributed to omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). EPA and DHA make the blood less likely to clot, reduce elevated blood triglycerides (fats), protect the lining of brain cells and may also prevent the buildup of beta amyloid, a protein involved in Alzheimer's disease.

Not all fish are packed with omega-3s, though. Fatty fish such as salmon, trout, anchovies, Arctic char, herring, mackerel and sardines are good sources. Canned tuna is an okay source, while tilapia, sole, cod, pollock (e.g. fish sticks), scallops and shrimp are low in omega-3 fatty acids.

Fish delivers other nutrients, too. B vitamins, vitamin D, selenium and certain proteins in seafood may also confer health benefits.

Concerns about toxins, mercury

Chemicals such as mercury, industrial toxins like PCBs (polychlorinated biphenyls) and pesticides that are released into the air and water and can end up in fish.

These contaminants make their way into the plants and sea animals that fish eat. As smaller fish are eaten by larger, longer-living species, toxins build up and become concentrated in fish.

The biggest concern is mercury, a metal that can affect the nervous system, making the developing fetus and young children especially vulnerable. Studies have found that children exposed to high levels of mercury during pregnancy have learning disabilities, impaired hearing and poor motor skills.

Cooking fish has little impact on mercury content.

To minimize mercury exposure, women of childbearing age, especially women who are pregnant and breastfeeding, and children younger than 11, should avoid eating high-mercury fish, which include swordfish, shark, marlin, orange roughy, bigeye tuna and king mackerel.

What about canned tuna?

Fish used in canned tuna are typically younger and smaller and have less mercury than fresh tuna. Canned light tuna which contains skipjack, yellowfin and tongol species is relatively low in mercury.

Canned albacore, or white, tuna is higher in mercury than light tuna. Health Canada advises women who are or may become pregnant or are breastfeeding to consume no more than 10 ounces (about two 170-gram tins) per week.

Kids aged five to 11 should eat no more than five ounces (one 170-gram tin) of albacore tuna per week and younger children, ages one to four, no more than one-half tin per week. The U.S. FDA recommends that children should not eat fish, including low-mercury species, until two years of age.

The sustainability issue

Choosing fish that are farmed or fished responsibly is also an important consideration. Sustainable fish and seafood are caught in a way that doesn't harm the marine environment or other species of fish. They are also species that are not overfished.

Eco-certification labels at the fish market and on restaurant menus can help you make a sustainable decision. Farm-raised seafood that's certified sustainable means that it's grown and harvested at fisheries and aquaculture operations in a sustainable manner.

A label stating "eco-certified" on wild-caught fish means that the fishery is certified. Buying eco-certified wild-caught fish avoids species at risk of being overfished or caught in a way that harms the marine environment.

Consumer seafood guides can also help make your purchasing decision simpler. Canada's Ocean Wise Seafood classification program ( indicates choices that are sustainable (Ocean Wise, recommended) or unsustainable (not recommended).

The Monterey Bay Aquarium's Seafood Watch Guide ( provides a list of choices that are high in omega-3s, low in mercury and raised or caught sustainably.

Best and worst fish choices

According to the Monterey Bay Aquarium, fish on the "super green" and "best choices" lists are good for both human health and the environment. They deliver omega-3 fatty acids, are low in mercury and are raised or caught responsibly.

Keep in mind that just because a certain type of fish isn't on one of these lists doesn't mean that it is not a healthy or sustainable choice. Consult the organization's downloadable guides to learn about other species.

Fish on the "avoid" list are overfished or caught or farmed in ways that harm the environment.

The "super green" List

Atlantic mackerel (Canada and United States, purse seine)

Coho salmon, freshwater (U.S.)

Pacific sardines (wild-caught)

Salmon (wild-caught from Alaska)

Salmon, canned (wild-caught from Alaska)

Other "Best Choices" (low in contaminants but lower in omega-3s than super-green choices)

Albacore tuna (troll- or pole-caught from U.S. or B.C.)

Sablefish/black cod (from Alaska and Canadian Pacific)


Abalone (China and Japan)

Cod (Atlantic: Canada and United States)

Cod (Pacific: Japan and Russia)

Halibut (Atlantic, wild)

Mahi-mahi (imported)

Orange roughy

Pollock (Canada, trawl)

Salmon (Atlantic, farmed)

Sardines (Atlantic, Mediterranean)


Swordfish (imported, longline)

Tuna, albacore (imported except troll, pole and line)

Tuna, bluefin

Tuna, skipjack (imported, purse seine)

Tuna, yellowfin (longline, except United States)

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