Mercury in Seafood: Which Fish Contains the Most and Least Mercury? (2024)

Seafood, particularly fish, is the most significant dietary source of mercury.

However, mercury concentrations in popular seafood can vary depending on the specific type of fish.

Mercury is a heavy metal and a neurotoxin. Since it can accumulate in the body, it can potentially lead to adverse health effects at high levels of exposure (1).

This article highlights the species of fish that contain the highest and lowest amounts of mercury, while also discussing some essential topics on the subject.

Information and Data Sources

Two extensive resources have been used to compile the data on mercury levels in this guide:

1. The FDA’s ‘Mercury Levels in Commercial Fish and Shellfish (1990-2012)’ (2)
2. ‘A Global-scale assessment of mercury concentrations and the identification of biological hotspots’ (3)

The first resource is part of the FDA’s monitoring program of mercury concentrations in fish and shellfish, which ran for over two decades. Multiple samples were taken for each species, and the mean mercury concentrations were calculated.

The second resource is a global-scale assessment of mercury concentrations published in 2019. This study by Buck et al. analyzed the mercury content of fish from 40 locations across 26 different countries.

Note: Not all fish in the second resource are common commercial species like those in the FDA’s monitoring program.

In this article, we will first explore the mercury levels found in commercial fish according to the FDA’s monitoring program. After this, we will look at the results from the global-scale assessment by Buck et al.

Study 1: Mercury Levels in Commercial Fish (FDA Data)

Here are the commercial fish and shellfish with the highest and lowest mercury concentrations, based on results from the FDA’s monitoring program.

Commercial Fish and Shellfish With the Most Mercury Content

The table below presents the commercial fish and shellfish that contain the highest levels of mercury.

The data is sourced from the FDA’s monitoring program and includes the name of each seafood product, its mean mercury content (PPM), and the number of samples used to determine the mercury level (1).

It’s important to note that PPM stands for ‘parts per million,’ which is equivalent to 1 mg per kilogram.

For instance, a mercury content of 1.0 PPM found in a 1-kilogram sample would mean a mercury content of 1.0 mg.

The Types of Fish With the Highest Mercury Levels

As indicated in the table, large species of fish like tilefish, swordfish, shark, and king mackerel tend to contain the most mercury.

The reason larger fish typically contain more mercury is largely due to a process called biomagnification.

Biomagnification occurs when the concentration of a compound, such as mercury, becomes greater in species higher up the food chain (4).

This happens because larger fish eat multiple smaller fish that already contain mercury from their environment. Since larger fish tend to have longer lifespans, they also have more time to accumulate mercury (5).

The United States Environmental Protection Agency (U.S EPA) sets a 0.3 PPM criterion of mercury in fish as a ‘health criteria’ (6).

The EPA states: “The resulting criterion of 0.3 mg methylmercury/kg in fish tissue should not be exceeded to protect the health of consumers” (7).

In this regard, a 2019 global-scale assessment of mercury concentrations in fish had some notable findings (3):

• Among 225 samples of carnivorous fish, 22% had mercury concentrations above 0.3 PPM (0.3 mg/kg).
• Across 30 samples of herbivorous fish, all samples had mercury content below 0.1 PPM.

This criterion is designed to guide health advisories regarding high-mercury fish and to inform regulatory and monitoring actions for seafood and specific water bodies.

Commercial Seafood With the Lowest Mercury Content

In the subsequent table, we can see various commercial seafood with the lowest mercury concentrations.

Once again, the data on mercury levels in each fish is sourced from the FDA’s monitoring program. For each species of fish and shellfish, you can see its mean mercury content (PPM) and the number of samples this information is based on (1).

Study 2: A Global Assessment of Mercury Levels In Seafood

Buck et al. published a study in 2019 that assessed mercury levels in seafood globally (3).

Firstly, this study made some expected observations:

• Piscivore and carnivore species of fish contained the highest concentrations of mercury. Piscivores are carnivores that have a diet of mainly fish.
• Omnivorous fish contained slightly lower mercury levels than carnivores, with detritivorous fish having similar levels.
• Herbivores and planktivores had the lowest mercury concentrations.

As previously mentioned, this study found that 22% of carnivorous fish had mercury concentrations higher than 0.3 PPM. In contrast, all herbivorous and planktivorous fish contained mercury at levels below 0.1 PPM.

Mercury Content By PPM Levels

The following lists display the key results of the study by Bock et al. showing fish with the highest and lowest mercury content within the following groups: piscivorous, carnivorous, omnivorous, and herbivorous.

In the lists, you can see the mercury level (PPM) each species contained, along with the number of samples that informed this result in brackets.

The common name of each fish is listed followed by the species’ scientific name in brackets.

Piscivorous Fish – Highest Mercury

1. Swordfish (Xiphias gladius): >1.2 PPM of mercury (4 samples)
2. Pacific bluefin tuna (Thunnus orientalis): >1.0 PPM of mercury (9 samples)
3. Albacore tuna (Thunnus alalunga): >0.8 PPM of mercury (6 samples)
4. Black scabberfish (Aphanopus carbo): >0.7 PPM of mercury (2 samples)
5. Wels catfish (Silurus glanius): >0.4 PPM of mercury (11 samples)
6. Bigeye thresher (Alopias superciliosus): >0.3 PPM of mercury (1 sample)
7. Wolf fish (Hoplias malabaricus): >0.3 PPM of mercury (6 samples)
8. Spotted sorubim (Pseudoplatystoma corruscans): >0.3 PPM of mercury (1 sample)

Piscivorous Fish – Lowest Mercury

1. Bluefin trevally (Caranx melampygus): <0.1 PPM of mercury (3 samples)
2. Longtail tuna (Thunnus tonggol): <0.1 PPM of mercury (9 samples)
3. Zander (Sander lucioperca): <0.1 PPM of mercury (9 samples)
4. Malabar snapper (Lutjanus malabaricus): <0.2 PPM of mercury (1 sample)
5. Mackerel tuna (Euthynnus affinis): <0.2 PPM of mercury (9 samples)

Carnivorous Fish – Highest Mercury

1. Spotted goatfish (Pseudupeneus maculatus): >0.4 PPM of mercury (3 samples)
2. Pacific halibut (Hippoglossus stenolepis): >0.3 PPM of mercury (7 samples)
3. Striped snakehead (Channa striata): >0.3 PPM of mercury (21 samples)
4. Fat snook (Centropomus parallelus): >0.3 PPM of mercury (3 samples)
5. Common snook (Centropomus undecimalis): >0.2 PPM of mercury (3 samples)

Carnivorous Fish – Lowest Mercury

1. Giant African threadfin (Polydactylus quadrifilis): <0.1 PPM of mercury (2 samples)
2. Tomato rockcod (Cephalopholis sonnerati): <0.1 PPM of mercury (1 sample)
3. Forkbeard (Phycis phycis): <0.1 PPM of mercury (1 sample)
4. Barramundi (Lates calcarifer): <0.1 PPM of mercury (9 samples)
5. Yellowfin goatfish (Mulloidichthys vanicolensis): <0.1 PPM of mercury (3 samples)

Omnivorous Fish – Highest Mercury

1. Common bream (Abramis brama): >0.4 PPM of mercury (14 samples)
2. Armored catfish (Pareiorhaphis grosskopfi): >0.3 PPM of mercury (2 samples)
3. Common carp (Cyprinus carpio): >0.3 PPM of mercury (10 samples)
4. Crucian carp (Carassius carassius): >0.3 PPM of mercury (2 samples)
5. Dusky stingfish (Sebastiscus marmoratus): >0.2 PPM of mercury (3 samples)

Omnivorous Fish – Lowest Mercury

1. Yellowtail catfish (Pangasius pangasius): <0.1 PPM of mercury (1 sample)
2. Indian mackerel (Rastrelliger kanagurta): <0.1 PPM of mercury (3 samples)
3. Mozambique tilapia (Oreochromis mossambicus): <0.1 PPM of mercury (5 samples)
4. Twospot astyanax (Astyanax bimaculatus): <0.1 PPM of mercury (1 sample)
5. Humpnose big-eye bream (monotaxis sp.): <0.1 PPM of mercury (1 sample)

Herbivorous Fish

Every herbivorous species of fish sampled in the study had low mercury content.

However, all of the following fish species contained less than 0.05 PPM of mercury:

• Rohu (L. Rohita): <0.05 PPM of mercury (2 samples)
• Mrigal carp (Cirrhinus cirrhosus): <0.05 PPM of mercury (5 samples)
• Nile tilapia (Oreochromis niloticus): <0.05 PPM of mercury (5 samples)
• Silver carp (Hypopthalmichthys molitrix): <0.05 PPM of mercury (2 samples)
• Bocachico (Prochilodus magdalenae): <0.05 PPM of mercury (4 samples)
• Blue tilapia (Oreochromis aureus): <0.05 PPM of mercury (8 samples)

Nuance Required: Seafood Is a Healthy Choice

While mercury in seafood is a genuine concern and there are health advisories surrounding it, it is important to view the topic with nuance.

This is because seafood consumption, generally speaking, has a net benefit for human health. Seafood is high in protein, contains a broad range of vitamins and minerals, and oily fish offers significant levels of omega-3 fatty acids.

On this topic, a 2020 umbrella review of systematic reviews and meta-analyses examined the associations between 55 health outcomes and fish consumption levels (8).

This review found that fish intake was (8):

• “Generally safe”
• “Reduces all-cause mortality, cardiovascular disease, cancer, and other outcomes”
• Has the “largest risk reduction at 2-4 servings/week”

Health Advisory From the FDA on Fish Intake

Health advice from the FDA makes their stance on fish consumption clear.

This advisory states: “while it is important to limit mercury in the diets of those who are pregnant or breastfeeding and children, many types of fish are both nutritious and lower in mercury” (9).

The FDA also state that: “strong evidence shows that eating fish, as part of a healthy eating pattern, may have heart health benefits” (9).

The FDA also lists their ‘best choices’ and ‘choices to avoid’ for seafood.

‘Best Choices’

The FDA’s ‘best choices’ for seafood are as shown below:

• Anchovy
• Atlantic croaker
• Atlantic mackerel
• Black sea bass
• Butterfish
• Catfish
• Clam
• Cod
• Crab
• Crawfish
• Flounder
• Haddock
• Hake
• Herring
• Lobster
• Mullet
• Oyster
• Pacific chub mackerel
• Perch
• Pickerel
• Plaice
• Pollock
• Salmon
• Sardines
• Scallop
• Shad
• Shrimp
• Skate
• Smelt
• Sole
• Squid
• Tilapia
• Trout, freshwater
• Tuna, canned light (includes skipjack)
• Whitefish
• Whiting

‘Choices to Avoid’

The FDA’s ‘choices to avoid’ for seafood all have high mercury levels and are listed below:

• King mackerel
• Marlin
• Orange roughy
• Shark
• Swordfish
• Tilefish (Gulf of Mexico)
• Bigeye tuna

To explore the FDA’s advice on eating fish in more detail, please refer to this resource:

FDA Advice on Eating Fish

Further Resources

• Oily fish with the highest omega-3 content
• A guide to different types of seafood
• ‘Advice About Eating Fish’ (FDA)
• Factsheet: ‘Mercury and Health’ (World Health Organization)
• 15 Types of Canned Fish With Nutrition Facts + Mercury Content

References

1. https://www.epa.gov/mercury/health-effects-exposures-mercury
2. https://www.fda.gov/food/environmental-contaminants-food/mercury-concentrations-fish-fda-monitoring-program-1990-2010
3. https://pubmed.ncbi.nlm.nih.gov/31412499/
4. https://www.merriam-webster.com/dictionary/biomagnification
5. https://pubmed.ncbi.nlm.nih.gov/17894202/
6. https://www.epa.gov/mercury/resources-mercury-science-and-research
7. Water Quality Criterion for the Protection of Human Health (EPA)
8. https://www.sciencedirect.com/science/article/abs/pii/S0924224419310532
9. https://www.fda.gov/food/consumers/advice-about-eating-fish#choice