The Worst Seafood to Eat

While only imported longline-caught swordfish is considered unsustainable, in general the fish should be avoided because of its potentially high mercury levels and the possible presence of nematodes or other parasites — though its high levels of nutrients are thought to justify an occasional meal.

Marlin can have higher levels of mercury than swordfish. In addition, the fisheries for many types of the fish are considered poorly managed, and sea turtles, sharks, and seabirds may be taken as bycatch.

Many species of shark have sky-high mercury levels, and shark meat has meager nutritional value, so there’s little reason to eat it. Declining populations are also a problem because of the shark’s essential role in the food chain. Seafood Watch makes an exception for the shark also called spiny dogfish when it’s fished in the United States.

Tilefish could be the unhealthiest fish of all, with extremely high levels of mercury wherever it’s harvested around the world. Those levels are double in tilefish from the Gulf of Mexico. Some tilefish is also taken by unsustainable fishing methods.

Unlike its smaller, healthier cousins in the mackerel family, the king mackerel — also known as Spanish mackerel — is large enough to guarantee that it will contain a higher level of mercury.

The first thing you should know about this fish is that an alternative name for it is slimehead. According to Greenpeace, “Many orange roughy stocks have already crashed…and recently discovered stocks are decreasing rapidly. In addition, it is slow-growing — it can live to be 100 years old — so it has a lot of time for the bioaccumulation of mercury.

Highly valued as a delicacy — the owner of a Japanese sushi chain paid $3.1 million for a 613-pound specimen earlier this year — bluefin tuna is one of the most endangered major marine species. Populations of all three varieties — Atlantic, Pacific, and Southern — have declined precipitously in the past few decades. As a food item they are to be avoided for their high levels of toxins.

Bigeye is one of two species of tuna called ahi, and like other tuna is high in mercury. Conservationists urge that consumers choose tuna other than bigeye because of its diminishing numbers due to unsustainable fishing practices, including so-called IUU (illegal, unregulated, and unreported) harvesting by pirate longliners.

Like all tuna, yellowfin — the other species marketed as ahi — is extremely nutritious, but like other large fish, it is contaminated by mercury. Compared with other tuna species, it has about the same amount of mercury as albacore, twice the amount of skipjack, and half as much as bigeye. Yellowfin is overfished, and sea turtles, sharks, and seabirds are often taken as bycatch.

Tilapia is generally a safe bet and a healthy, inexpensive choice, but origin is important. Avoid tilapia from China, where concerns include illegal use of antibiotics by farmers and widespread escape of the fish from flooded farming regions and subsequent impact on local wild species. Some health authorities warn against tilapia because of its high Omega-6 content, but the American Heart Association says that “Omega-6 fats are not only safe but they are also beneficial for the heart and circulation.”

Atlantic cod fisheries collapsed in the 1990’s, and 2016 saw their lowest numbers in recent years. Two rebuilding programs for major fisheries are now in progress with a goal of stabilizing populations in this decade, but for now, Atlantic cod — also known as scrod — should be off the table.

While Pacific populations of flatfish, such as flounder, sole, and halibut, are generally stable and healthy, their Atlantic cousins suffer from overfishing — though there are current initiatives to rebuild the stocks. The International Union for Conservation of Nature lists Atlantic halibut as endangered. Depending on where they’re fished, these species may also contain substantial quantities of mercury and/or PCBs.

It isn’t a true bass, it doesn’t always come from Chile, and its original name was Patagonian toothfish, but Chilean sea bass is one of the most popular of food fishes, prized for its delicious meat. Unfortunately, it’s high in mercury and vastly overfished, and its declining numbers potentially affect its marine environment negatively.

With some exceptions, most eel — American, European, or Japanese — is raised under conditions that encourage the use of potentially harmful chemicals, and disease is common. In addition, effluents discharged from eel farms may harm native populations — and overfishing threatens wild eels.

Often raised in crowded pens, these fish may be fed antibiotics to fend off disease and parasites. They also accumulate PCBs. Parasites and diseases from salmon pens can spread to nearby wild stocks. In addition, farmed salmon is typically fed on other fish, and it takes about three pounds of wild fish to produce one pound of farmed salmon.

A type of Vietnamese catfish, swai is often pond-raised with hyper-intensive production methods that generate toxic substances.

About 90% of the shrimp Americans eat is imported, and most imported shrimp comes from farms in Southeast Asia and Central America. Asian shrimp farms have in many cases replaced environmentally important mangroves. From a health perspective, much imported shrimp contain antibiotics that are not approved in the U.S., as well as 4-hexylresorcinol, considered hazardous by OSHA.

About half the king crab consumed in the U.S is from Russia’s Berent Sea. Russian fisheries are thought to be poorly managed from an environmental point of view, and, because the king crab is an invasive species in Russian waters, it is having a negative impact on the ecology.

There are more than 85 grouper species worldwide. Slow to reproduce, most are threatened by overfishing. (U.S. grouper fisheries typically set catch limits that are higher than those recommended.) They have also been subject to consumption warnings because of their mercury levels.

Light in color and sometimes said to resemble lobster in flavor and texture, this popular fish is recovering from depletion, but the trawling and dredging methods used for the catch is destructive to marine habitat.

Perhaps the Gulf of Mexico’s most famous fish, red snapper has been seriously overfished, and fishery managers allow a catch that’s 50% higher than recommended. In addition, bycatch — of sharks, groupers, porgies, and other species — accounts for a staggering 44% of the total taken.