Top 10 Worst Fish to Eat (Don’t Eat These Dirty Fish!)

Fish is generally considered a healthy food choice, but not all fish are alike. You could be eating the healthiest, best fish for weight loss, or you could be unknowingly eating a dirty fish that’s actually bad for you.

There are certain fish species that can contain high levels of mercury, which can cause you more harm than good health. Mercury can lead to serious health problems and can even contribute to obesity and malfunctioning metabolism.1

While some fish are good for weight loss, some fish species you should really avoid. Not only because of high mercury levels but also because they aren’t healthy for you and can even cause you to gain weight.

The Dirtiest Fish You Can Eat

Quick Answer: Tilefish from the Gulf of Mexico is the dirtiest and worst fish you can eat. FDA testing has found that Tilefish contain the highest levels of mercury by far. This fish is the worst in mercury. It’s best not to eat Tilefish ever.

The American Heart Association recommends eating fish as part of a healthy diet to fight heart disease.2 Fish is naturally high in healthy omega-3s that have been found to lower the risk of heart disease. If you have high blood pressure, the omega-3s in fish and seafood can lower your levels.3

Eating a diet rich in healthy fish can help you lose weight.4 Fish is high in protein and contains healthy omega-3 fatty acids and other vitamins like vitamin B12, which are also really good for your health.5 The FDA recommends 8 ounces of seafood per week based on a 2,000-calorie diet.

But it’s not a great idea to eat fish daily because of its mercury content. Mercury is by far one of the biggest health dangers of eating fish. Mercury is a neurotoxin that damages your brain and nervous system.6

Mercury can cause serious developmental damage to children.7 According to the FDA, pregnant women or those breastfeeding should limit their fish consumption to 8-12 oz. per week and only eat fish species with low mercury levels.

The top 10 ranking of dirty fish that are highest in mercury are:

  1. Tilefish
  2. Swordfish
  3. Shark
  4. Mackerel King
  5. Tuna
  6. Orange Roughy
  7. Marlin
  8. Grouper
  9. Bluefish
  10. Sablefish

Farmed Atlantic Salmon

Test salmon fish in laboratory control of mercury and toxic dye

Farmed Atlantic Salmon is one of my most hated fish, and I affectionately call it the “Evil Twin.” It’s unfortunate that most people who unknowingly pick up this bad farmed salmon in the grocery store are putting themselves at risk for some serious health problems.

Now, farmed salmon will be a lot cheaper than wild-caught salmon, but the latter will be worth the extra price. Farmed fish contains higher levels of saturated and polyunsaturated fats than wild-caught salmon.8 Because of these fats, farmed salmon also contains almost 50% more calories.

Farmed Atlantic Salmon are fed a soy-based diet, and they’re found to be high in toxic Polychlorinated Biphenyls (PCBs).9 These PCBs are really bad for your health and can even lead to cancer.10 They’re hormone disruptors that can negatively impact your metabolism by altering your testosterone and estrogen levels.11

Many farm-raised salmon are dyed pink to make it look like they have the same bountiful omega-3s as their “Good Twin” Alaskan Wild-Caught Salmon.12

Now, farmed salmon contains about the same amount of omega-3s as wild-caught salmon. But the problem is that farmed salmon contains almost six times the amount of omega-6 fats. Eating too many omega-6s can lead to inflammation, heart disease, and weight gain.13

This is why it’s a smart idea to supplement with an omega-3 like the one in my OmegaKrill review. It’ll help to rebalance your omega-3 to omega-6 ratio, which will reduce inflammation in your body.

While having only 1/4 the vitamin D as Alaskan Wild-Caught Salmon, farmed salmon are crammed into pens where diseases and parasites can flourish. This requires the farmers to use antibiotics and pesticides on the farm-raised salmon that make their way onto your plate.

Disturbingly enough, the FDA approved genetically engineered salmon in November 2015 without requiring consumer labeling. This study found farmed salmon to actually cause weight gain in mice.14 The mice also showed signs of metabolic syndrome and type 2 diabetes.

Atlantic Bluefin Tuna

bluefin tuna

The New York Times found Atlantic Bluefin Tuna to have the highest amounts of mercury than any other tuna.15 Mercury is not only toxic to you, but it can also cause weight gain by disturbing your thyroid glands and pancreas. Both of which are extremely vital to regulating your hormones.

The International Union for Conversation of Nature has deemed Atlantic Bluefin Tuna to be extremely over-harvested and at risk for near extinction.

It’s much easier and better for your belly to eat canned light tuna instead of this mercury-laced fish. Even albacore tuna contains a higher amount of mercury, which is why picking out a light canned tuna or canned sardines will be a better seafood option.


group of tilapia swimming in farm

This might shock you, but most restaurants and quick-service eateries use tilapia for their fish. Just about every tilapia in grocery stores and restaurants is actually a dirty and bad fish.

Most tilapia are farm-raised and fed a corn-based diet when they should be out in the wild, eating lake plants and algae. In lower-quality farms, tilapia are also usually fed chicken and pig feces, which leads to the build-up of bad bacteria and toxins in the fish.

Farmed tilapia are also susceptible to parasites like Nematodes, Tapeworms, Protozoans, and Flukes. I wouldn’t eat farmed tilapia from China due to their low farming practices and environmental standards. China uses antibiotics and chemicals on their farmed tilapia, low feed quality, water pollution and low regulations.

Farmed tilapia are overcrowded and subjected to high water pollution, such as ammonia. To manage diseases, these fish are often given antibiotics and chemicals. These antibiotics and chemicals can leave a residue on the fish, causing allergic reactions or health problems.

Pesticides and more contaminant exposure are also high in farmed tilapia. These pesticides can get into your body when eaten. This can negatively contribute to your gut health. This not only causes digestive gut problems but also reduces the immune system.

Tilapia has higher levels of omega-6 fatty acids and low levels of beneficial omega-3 fatty acids. While omega-3s have been found to lower abdominal fat, omega-6 fatty acids have been associated with an increase in stomach fat.16


swordish eating a smaller fish in the ocean

If you’re going to eat swordfish, you might as well start drinking a big glass of mercury right now. Swordfish are high on the marine food chain, live a long life, and thus contain high levels of mercury from all the fish they eat.

Swordfish eat smaller fish, and by a process known as biomagnification, they get a build-up of mercury. Mercury is a well-known endocrine hormone disruptor that can wreak havoc on your thyroid and pancreas.

Mercury disrupts the functioning of your thyroid gland, which regulates your metabolism, body temperature, and other critical body functions. This causes your hormones to get out of whack, causing you to start storing more fat. Hypothyroidism from mercury slows your metabolism and leads to weight gain.

Even low levels of mercury over time can harm your body’s energy system balance.17 This metabolic disruption leads to impaired antioxidant defense, increased inflammation, disrupted insulin levels, and damaged lipolysis (fat burning).

Marlin and Sailfish are two closely related high mercury fishes that should stay off the menu.

Fish Sticks

fish sticks are bad for you

This might be a no-brainer, but I thought I’d include fish sticks on my list of the worst fish for weight loss. They usually used lower-quality farmed white fish such as cod, haddock, pollock, and tilapia.

Fish sticks are heavily processed, breaded, and fried in processed fats. The frying process usually uses bad seed and vegetable oils, like canola oil. These bad vegetable oils can cause inflammation, weight gain, and hormone disruption.

Just one fish stick contains 78 calories. Most people eat at least six fish sticks at a time, which is almost 500 calories. You’ll be better off eating chicken nuggets than fish sticks. Fish sticks are also high in sodium, which can cause weight retention and high blood pressure.

If you love fish sticks and won’t give them up, be sure to search for them that are reduced fat and baked instead of fried.

Eel / Unagi

Eel is a popular choice for sushi, and it can be found at virtually every sushi restaurant on the planet. I’ve eaten at many sushi places in my day and, for the longest time, thought eel was good for me.

With the rise in popularity in eating eel sushi, their numbers have been greatly depleted and are now considered endangered. Eels are considered a “dirty fish” because they’re bottom feeders.

Eels chew up everything that’s rotten or dead on the water floor. They can then build up contaminant levels since they absorb these pollutants in the waters they live in. Heavy metals and PCBs (polychlorinated biphenyls) from industrial waterways enter their bodies.

Luckily, it’s not a popular choice for fish, but it can be dangerous if you like to eat sushi a lot.


Sharks are at the very top of the food chain, which means they are extremely high in mercury. All the fish they consume that contain mercury build up in their body via a process called biomagnification.

Sharks can contain other harmful chemicals other than mercury, like PCBs and dioxins. These chemicals are known to cause cancer and health issues.

Sharks’ tissues contain higher levels of urea (pee). Without proper handling, this tissue urea can break down the toxic ammonia.

They are also very low in protein and omega-3 fatty acids. Sharks are just not a smart choice for healthy fish that will help you lose weight.

Additionally, shark consumption can cause the ocean ecosystems to suffer since they’re at the top of the food chain. Without them, rays and jellyfish become overpopulated, leading to the suffering of the rest of the ecosystem.


tilefish bad for you

There isn’t much to say about Tilefish other than you should skip them at all costs. Their mercury levels are so high that general medical advice is not to eat them. Tilefish are high on the food chain and live longer lives, resulting in high levels of mercury.

The FDA tested tilefish caught in the Gulf of Mexico for the highest mercury level of all fish. Tilefish from the Atlantic Ocean contain less mercury but should still be limited in consumption.

The Environmental Defense Fund (EDF) recommends that pregnant women, nursing mothers and children not eat Tilefish, whether from the Gulf of Mexico or the Atlantic.18 It’s best to avoid this seafood altogether.

King Mackerel

king mackerel bad for you

King Mackerel contains such a dangerous amount of mercury that even health officials warn against eating it. This predatory fish feeds on smaller fish with mercury in their systems.

Mercury builds up in smaller fish and doesn’t break down in the environment. Mercury in the environment is mostly from industrial pollution. Coal-fired power plants release mercury into the air and deposits into the oceans.

King Mackeral also have a long lifespan, which gives them more time to build up mercury in their bodies. Their larger size compared to other smaller fish also increases their mercury exposure.

If you love King Mackerel, limit your consumption to one that’s less than 33 inches in size. You should eat no more than one 3.5-ounce serving of cooked King Mackerel per month.

Imported Shrimp

Shrimp normally would be on the approved fish list for weight loss, but considering that 90% of shrimp in the U.S. are imported, there are things you need to know about.

Countries use antibiotics and other chemicals in shrimp farming to combat diseases in these overcrowded ponds. These antibiotics and chemical residues stay in the shrimp and can even lead to antibiotic resistance in people.

Imported shrimp are a “dirty fish” because they’re farmed in unsanitary conditions. Shrimp farming and processing facilities usually lack the highest hygiene and sanitary standards, which can cause the shrimp to become infected with pathogens like salmonella and E. coli.

Shrimp are lacking in nutrition, and imported ones are high in contaminants. There isn’t much regulation for shrimp in foreign countries, and you can expect to find chemical residues, antibiotics, and even traces of E. coli.

Shrimp is fine when bought domestically, and it even has a good amount of iodine, which can be good for your thyroid. Just be sure to search out for domestic shrimp instead of the gross imported ones.


Catfish are bottom feeders, a “dirty fish,” and they don’t deserve a spot on your dinner plate. Catfish have their whiskers (barbels) to detect food on the water floor in murky and muddy environments.

Catfish feed on plants, insects, and dead material (detritus) on the water floor, earning them a reputation as dirty fish. They live in muddy waters that can cause them to absorb pollutants.

But catfish that is caught from clean waters is generally considered safe to eat. U.S. farmed catfish is considered a safer fish to eat due to strict regulations for their farming practices. Raising catfish in controlled aquaculture environments significantly reduces their exposure to pollutants.

Unfortunately, 90% of the imported farmed catfish come from Vietnam, where antibiotics are also used. The Federal Government doesn’t consider this imported catfish from Vietnam (Swai and Basa) to technically even be catfish, so they’re not held to the same inspection rules.

Orange Roughy

Orange Roughy

Orange Roughy is a deep-sea fish that contains high levels of mercury. This fish can live to 150 years old and feeds on smaller fish, which makes it very easy to build up high levels of mercury.

This fish doesn’t have the best health benefits since it’s low in protein and omega-3 fatty acids. Other oily fish, like wild-caught salmon, are a much better choice if you want a fish with maximum health benefits.

Plus, Orange Roughy is extremely susceptible to overfishing since it takes so long for its species to mature. It’s best to avoid this species of fish to avoid its high mercury levels and the sustainability of its species.


Eating more fish and seafood is generally recommended medical advice. The healthy omega-3 fats found in fish have many benefits, including brain health and heart health. Omega-3 fatty acids help with weight loss by suppressing appetite, increasing metabolism, reducing fat storage, lowering inflammation, and improving the body fat-to-muscle ratio.

In the battle of fish oil vs krill oil, both have their advantages. Be sure not to skip krill oil, which contains astaxanthin, which research has found to be the most powerful antioxidant found in nature. Ideally, you’d take both krill oil and fish oil to maximize the benefits.

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But there are still some dirty fish on the list that you should avoid. Mostly because of their high mercury levels. This is why it’s not a good idea to eat fish every day. It’s also a good idea to eat a variety of good fish instead of just one species.

If you’re thinking about becoming pregnant, are pregnant, or are breastfeeding, then it’s a good idea to talk to your doctor first before eating a lot of seafood. Be sure to follow the FDA’s guidelines on fish consumption and to eat lower-mercury fish.

Eating fish can also be bad for the environment, depending on the species and whether the fish was caught in the wild or farmed. Seafood sustainability is important to ensure oceans can maintain their ecosystem balance for generations to come.19