Seafood You Should Think Twice About Before Ordering

Many foods from a range of diets are often touted as healthy and while some may be healthier than others, it almost seems that everyone would agree that fish is generally acknowledged as one of the healthiest foods you can ingest. This lean source of protein is rich in nutrients like Omega-3 fatty acids, which are essential for brain and heart health, as well as certain vitamins and minerals that are also said to aid skin and muscle strength. Even the American Heart Association recommends eating at least two servings of fish per week.

However, not all fish are created equal, and when it comes to which ocean dwellers you should dine on, it is important to be aware of which species are beneficial and which ones may cause harm when consumed. Many species, especially the larger ones, can contain harmful levels of mercury, posing serious health risks, particularly for children and pregnant women. It's best to avoid fish high in mercury and limit consumption of others to once a week(or you can play it even safer and be like Joey Chestnut, the reigning champion of Nathan's Hot Dog Contest who just signed with plant-based Impossible Foods).

Health concerns aside, there are environmental and ethical reasons to be selective about the fish you eat. Overfishing, illegal practices, and bycatch threaten many species, some to the point of extinction. Bycatch also harms non-target species like sea turtles and seabirds. Farmed fish, while convenient, come with their own set of problems, including disease, pollution from antibiotics, and genetic interference with wild populations. (Another factor polluting the oceans is plastic waste, which is 10 times worse now than in the previous four decades.)

24/7 Tempo reviewed recommendations and warnings from numerous environmental and medical websites, some of which include the Monterey Bay Aquarium's Seafood Watch, Greenpeace, Sustainable Fisheries, the National Oceanic and Atmospheric Administration's Fisheries site, and Medical News Today to determine which seafood options you should never choose (or at least eat sparingly) — for health or environmental reasons, or both.

Here are seafood options you should never choose:

• Why you should avoid: High in mercury and parasites
• Farmed or wild-caught: Wild-caught

While only longline-caught swordfish that is imported 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.

• Why you should avoid: High in mercury, depleted populations, risks to other species
• Farmed or wild-caught: Wild-caught

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

• Why you should avoid: High in mercury, depleted populations, risks to other species
• Farmed or wild-caught: Wild-caught

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.

• Why you should avoid: High in mercury
• Farmed or wild-caught: Wild-caught

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, and some tilefish are also taken by unsustainable fishing methods.

• Why you should avoid: High in mercury
• Farmed or wild-caught: Wild-caught

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.

• Why you should avoid: High in mercury, depleted populations
• Farmed or wild-caught: Wild-caught

The alternative name for this fish is enough reason to avoid it – slimehead – and 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.

• Why you should avoid: High in mercury and PCBs, severely depleted populations, risks to other species, illegal fishing
• Farmed or wild-caught: Wild-caught

Bluefin tuna is one of the most endangered major marine species in the world. It is highly valued as a delicacy — the owner of a Japanese sushi chain paid $3.1 million for a 613-pound specimen earlier this year and 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.

• Why you should avoid: High in mercury, destructive fishing methods, illegal fishing
• Farmed or wild-caught: Wild-caught

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.

• Why you should avoid: High in mercury, destructive fishing methods, illegal fishing
• Farmed or wild-caught: Wild-caught

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.

• Why you should avoid: Dosed with antibiotics, negative habitat impact
• Farmed or wild-caught: Farmed

Like with many fish, the origin is extremely important. Tilapia is generally safe and it's a healthy, inexpensive choice, but you should 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."

• Why you should avoid: Vulnerable to extinction
• Farmed or wild-caught: Wild-caught

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

• Why you should avoid: Potentially high in mercury, PCBs, and other contaminants; declining populations
• Farmed or wild-caught: Wild-caught

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.

• Why you should avoid: High in mercury, declining populations, illegal fishing, negative habitat impact
• Farmed or wild-caught: Wild-caught

Originally called Patagonian toothfish, this fish isn't a true bass and doesn't always come from Chile (it was renamed Chilean sea bass to make it more attractive to consumers and it worked – it's 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.

• Why you should avoid: Contaminants, negative habitat impact (farmed), declining populations (wild-caught)
• Farmed or wild-caught: Mostly farmed

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.

• Why you should avoid: High in PCBs and other contaminants, negative habitat impact
• Farmed or wild-caught: Farmed

Farmed fish are often raised in crowded pens, and may be fed antibiotics to fend off disease and parasites. They also accumulate PCBs (Polychlorinated biphenyls), a group of industrial chemicals. 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.

• Why you should avoid: High in Vibrio bacteria and other pollutants
• Farmed or wild-caught: Farmed

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

• Why you should avoid: High in contaminants, negative habitat impact
• Farmed or wild-caught: Farmed

Americans love shrimp but about 90% of the shrimp consumed in the U.S. 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, many imported shrimp contain antibiotics that are not approved in the U.S., as well as 4-hexylresorcinol, considered hazardous by OSHA.

• Why you should avoid: Overfishing, negative habitat impact
• Farmed or wild-caught: Wild-caught

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 harming the ecology.

• Why you should avoid: High in mercury, declining populations
• Farmed or wild-caught: Wild-caught

This fish is notoriously slow to reproduce, and although there are more than 85 grouper species worldwide, 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.

• Why you should avoid: Negative habitat impact
• Farmed or wild-caught: Wild-caught

Light in color and sometimes said to resemble lobster in flavor and texture, the trawling and dredging methods used for the catch are destructive to marine habitats, and while monkfish numbers have been on the rise, they still have a high mortality rate.

• Why you should avoid: Declining populations, negative habitat impact
• Farmed or wild-caught: Wild-caught

Red snapper is perhaps one of the most famous fish from the Gulf of Mexico and has been seriously overfished. Fishery managers allow a catch that's 50% higher than recommended, and in the case of bycatch — sharks, groupers, porgies, and other species — it accounts for an astonishing 44% of the total taken.