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.
Two extensive resources have been used to compile the data on mercury levels in this guide:
The FDA’s ‘Mercury Levels in Commercial Fish and Shellfish (1990-2012)’ (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.
Rank
Fish name (common)
Mean mercury content (PPM)
Number of samples
1
Tilefish (Gulf of Mexico)
1.123
60
2
Swordfish
0.995
636
3
Shark
0.979
356
4
Mackerel, King
0.73
213
5
Tuna, Bigeye
0.689
21
6
Orange roughy
0.571
81
7
Marlin
0.485
16
8
Mackerel, Spanish (Gulf of Mexico)
0.454
66
9
Grouper
0.448
53
10
Bluefish
0.368
420
11
Sablefish
0.361
26
12
Tuna, Albacore
0.358
451
13
Croaker, White
0.287
15
14
Halibut
0.241
101
15
Weakfish
0.235
46
16
Scorpionfish
0.233
6
17
Mackerel, Spanish (South Atlantic)
0.182
43
18
Mahi Mahi
0.178
29
19
Bass
0.167
101
20
Snapper
0.166
67
Table 1: Fish and shellfish with the highest mercury levels, in descending order, based on data from the FDA’s ‘Mercury Concentrations in Fish’ monitoring program
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.
Key Point: Tilefish, swordfish, shark, and king mackerel contain the highest concentrations of mercury. Most of the fish with high mercury levels are larger, predatory fish.
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).
Rank
Fish name
Mean mercury content (PPM)
Number of samples
1
Scallop
0.003
39
2
Clam
0.009
15
3
Shrimp
0.009
40
4
Oyster
0.012
61
5
Sardine
0.013
90
6
Tilapia
0.013
32
7
Salmon (canned)
0.014
19
8
Anchovies
0.016
15
9
Salmon
0.022
94
10
Catfish
0.024
59
11
Squid
0.024
36
12
Pollock
0.031
95
13
Crawfish
0.033
46
14
Shad
0.038
15
15
Mackerel, Atlantic
0.05
80
16
Mullet
0.05
20
17
Whiting
0.051
13
18
Haddock
0.055
50
19
Flatfish
0.056
71
20
Butterfish
0.058
89
Table 2: Fish and shellfish with the lowest mercury levels, based on data from the FDA’s ‘Mercury Concentrations in Fish’ monitoring program
Additionally, some shellfish not included in the FDA’s monitoring program, such as conch and whelk, appear to have very low mercury content.
Key Point: Seafood with the lowest mercury content includes shellfish like clams, shrimp, scallops, and oysters. Small fish, such as sardines and anchovies, also have low levels of mercury.
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
Swordfish (Xiphias gladius): >1.2 PPM of mercury (4 samples)
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)
Key Point: As shown in this study, piscivorous and carnivorous fish, fish that eat other fish, tend to accumulate the highest levels of mercury.
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).
“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:
Michael works as a nutritionist in a community setting and holds a Master's Degree in Clinical Nutrition. He is a Registered Associate Nutritionist with the Association for Nutrition.
