Mercury per serving of fish
Fish
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Mercury concentration
ppm
Serving size
oz
Mercury per serving
µg
Percentage of your weekly safe limit of mercury
Your weight
lb
Weekly safe limit
µg
Percentage
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Use our fish mercury calculator to determine the mercury level in the fish you consume and how much you can safely consume in a week. Mercury is a toxic metal found in all fish due to the low levels of mercury found in all aquatic environments. Larger fish higher up on the food chain have higher mercury levels, which can pose neurological health risks to those who consume too much. Fish are an essential source of protein and omega-3 fatty acids, but it is vital to choose to consume species that are healthy for our bodies as well as those sustainably fished. So, check out our fish mercury calculator to learn more about what's on your plate!

How does mercury get into fish?

The form of mercury that we are talking about is actually methylmercury, which comes from both human and natural sources. Mercury is naturally found in the earth’s ocean and crust, but a big portion of the mercury in the ocean comes from burning fossil fuels, which is transferred from the atmosphere to oceans and lakes by rain. However, mercury does not get incorporated into the food chain until it is methylated by aquatic microbes and becomes methylmercury. Aside from these sources of mercury, there are also areas of the world that have significantly higher levels of methylmercury due to point source pollution by chemical plants.

So, how does mercury get into the fish? While methylmercury levels are low in the ecosystem itself, it bioaccumulates in larger fish that have consumed many smaller fish. Basically, methylmercury diffuses into phytoplankton, which are consumed by zooplankton, then by small fish, a larger fish, and so on. By the time a tuna eats its prey, it has consumed levels of methylmercury orders of magnitude higher than the surrounding environment.

What fish are high in mercury? Mercury levels in fish

Not all fish have the same levels of mercury within them. Fish that are higher up on the food chain will have higher levels of mercury. High mercury fish include predators such as marlin, swordfish, king mackerel, bigeye tuna, sharks, orange roughy, and tilefish. Low mercury fish include salmon, anchovies, herring, shad, sardines, trout, and mackerel.

We measure mercury levels in fish in parts per million (ppm) and these values range from as low as 0.04 ppm in whiting to 1.52 ppm in marlin. The mercury levels in our fish mercury calculator are the mean values published in a scientific review conducted by Karimi, Fitzgerald, and Fisher in 2012. However, there can be large variations in mercury levels even within a single species based on the location and whether it was farm-raised or wild. You can find more data on mercury levels in wild versus farmed-raised fish, as well as the minimum and maximum reported values for all species within the review.

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High-mercury fish
Marlin 1.517 ppm
Swordfish 0.893 ppm
Shark (all) 0.882 ppm
Tuna (wild bluefin) 0.796 ppm
Mid-level mercury fish
Grouper 0.417 ppm
Trout 0.344 ppm
Tuna (fresh Albacore) 0.317 ppm
Tuna (canned white) 0.328 ppm
Snapper 0.230 ppm
Low-level mercury fish
Catfish 0.118 ppm
Crab 0.098 ppm
Pollock 0.058 ppm
Shrimp 0.053 ppm
Salmon 0.048 ppm
Cod 0.087 ppm
Clams 0.028 ppm
Tilapia 0.019 ppm

Data source: Karimi, Fitzgerald, and Fisher, 2012

Let's talk tuna

As you will soon see, we chose tuna for our sample calculation below, and this is because tuna is the #3 most consumed seafood in the Unites States after shrimp and salmon. However, not all tuna are equal when it comes to mercury. Thankfully, this calculator functions as a tuna fish calculator for mercury, as we have included several different species. Canned tuna is the most commonly consumed type of tuna. Thankfully, canned "light tuna" has a fairly low mercury level, whereas canned "white tuna" falls in the mid-range. If you are eating fresh or frozen tuna, the species can have a big difference. Fresh skipjack, yellowfin, and albacore are all within acceptable mid-ranges for moderate consumption. However, bigeye and especially bluefin should be avoided as they are high mercury fish. Another good reason to avoid bluefin? It is an endangered species. If you are unsure of the type of tuna you are eating, it is best to go with the overall average value in our tuna fish calculator (0.450 ppm) to be safe.

How much mercury is in my fish dinner?

To calculate the amount of mercury in your fish dinner, first choose the type of fish from our drop-down menu. Next, input the serving size of your meal. Our fish mercury calculator will tell you the amount of mercury in your serving.

Mercury content per serving = serving size (g) * mercury concentration (ppm)

Say you are having a 4 oz tuna steak (113 g):

113 g * 0.45 ppm = 51.0 µg of mercury per serving

Not sure what the serving size of your meal is? A typical sushi roll has between 2-4 oz of fish, whereas a fish fillet varies between 4-6 oz. You can also calculate your recommended daily intake of protein as part of our macro calculator.

What is my weekly limit for mercury intake?

According to the Joint FAO/WHO Expert Committee on Food Additives (JECFA), you should consume no more than 1.6 µg mercury/kg body weight/week. Our fish mercury calculator takes into account your weight to tell you the percentage of your weekly allowance of mercury is in your current meal.

Safe weekly limit = 1.6 µg/kg/week * weight in kg

For example, if Isabella weighs 132 pounds (60 kg), she should consume a maximum of 95.8 µg of mercury per week.

Safe weekly limit = 1.6 µg/kg/week * 60 kg = 95.8 µg per week

Finally, the fish mercury calculator tells us that this 4 oz tuna steak is 53% of Isabella's weekly safe limit of mercury.

Percentage = mercury per serving / weekly safe limit

51.0 µg per serving / 95.8 µg per week = 53%

This tuna fillet is approximately half of your weekly safe limit of mercury. You should consume no more than two of these servings per week, or look for additional lower-mercury options if you wish to eat more servings of seafood within the week.

Health risks of mercury

Why are we concerned about mercury in the first place? Methylmercury is a neurotoxin and at high levels it can lead to paralysis and death. Mild methylmercury poisoning can cause numbness or tingling in the lips, fingers and toes, and at higher levels it can lead to deafness, blurred vision, and difficulties with speech and motor skills. While severe mercury poisoning from fish consumption is unlikely, consumption by pregnant mothers may result in developmental delays in their children, and thus expectant mothers and young children need to be especially careful about which fish they consume. It is recommended that pregnant mothers consume fish 2-3 times a week due to the heath benefits of omega-3 fatty acids; however, expectant mothers should choose low mercury fish to be sure to avoid any chance of mercury poisoning from fish.

So, should I still eat seafood?

Yes, as long as you make good choices based on both your own health and the environment.

The 2015-2020 Dietary Guidelines for Americans recommends that people consume 8 oz of seafood per week, or 8-12 oz for women who are pregnant or breastfeeding. Fish are beneficial for human health as they provide high levels of protein, vitamin D, vitamin B12, iron, and the polyunsaturated omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Those last two are associated with heart health. Just make sure to avoid choosing high mercury fish, or eat those species rarely.

In addition to choosing fish based on your health, you should also choose them based on the status of the fishery, the method by which they are caught, and the overall environmental impact. The Environmental Defense Fund and the Monterey Bay Aquarium have produced great resources that you can use to determine the best choices for sustainable fisheries as well as your health.

Carolyn Kovacs