Which Fish Have the Highest and Lowest Mercury Levels?

Methylmercury is the type found in fish. The fish with the highest mercury levels include King mackerel, shark, swordfish, tuna, and tilefish and the five fish with the lowest mercury levels include sardines, salmon, cod, catfish, and tilapia.

Are you avoiding high-mercury fish? Whether you’re pregnant or simply concerned about your neurological health, it pays to understand which fish have low mercury levels, as well as which ones to avoid. 

Read on to learn more about the symptoms of mercury poisoning and how to change your diet to avoid mercury toxicity.

There are two main forms of this compound: methylmercury and elemental mercury. Methylmercury exists nearly everywhere — in water, in our bodies, and in our food — though this doesn’t necessarily make it safer. In contrast, elemental mercury does not exist in food, but it can be found in everyday products.

Methylmercury is the type found in fish. Some fish, like swordfish, mackerel, and shark, contain extremely high levels of this organic compound. Others, like most types of salmon, don’t contain as much. It’s important to learn the difference between these two classes of fish — especially if you have small children or are currently pregnant.

Mercury is extremely poisonous, and it’s considered a neurotoxin as it can damage your nervous system. Breathing mercury vapor is more dangerous than swallowing it. Methylmercury is dangerous, especially to unborn babies, whether it’s consumed in large doses or over a long period of time. 

Symptoms of mercury poisoning include the following:

• Tingling in your hands and feet
• Trouble walking or moving around
• Weakness
• Loss of coordination
• Difficulty speaking or hearing
• Developmental issues in infants and children 

If you’re experiencing any of these symptoms and you consume a fish-heavy diet, you might want to speak with your doctor about whether methylmercury is a potential problem. The type of fish you’re eating matters, though, as many fish are high in mercury but others are safe to eat on a regular basis.

High-mercury fish should be reserved for special occasions, and you shouldn’t consume them when you’re pregnant. These fish include:

• King mackerel
• Shark
• Swordfish
• Tilefish
• Tuna (this includes canned tuna products)

In contrast, low-mercury fish and shellfish are good choices for almost anybody — including pregnant women and children. These include:

• Salmon
• Sardines
• Tilapia
• Catfish
• Cod (this includes many fish stick products)
• Shellfish like shrimp, scallops, and crab meat

Other fish and shellfish fall somewhere in between these extremes. Experts advise using caution in these cases — if you’re pregnant, trying to get pregnant, or breastfeeding, you might wish to avoid this category altogether. 

Otherwise, you could consider these medium-mercury fish:

• Carp
• Atlantic Ocean tilefish (as opposed to their high-mercury Gulf of Mexico relatives)
• Grouper
• Yellowfin tuna
• Albacore tuna

No, you shouldn’t stay away from all fish when you’re pregnant — but you should definitely avoid high-mercury fish. To be on the safe side, experts recommend up to three servings of fish per week from the low-mercury list or one from the medium-mercury list.

Whether you choose to completely avoid fish while you’re pregnant or not is up to you, of course (if you develop an aversion to fish that causes nausea, or if you’re allergic to fish, complete avoidance is understandable.) Still, low-mercury fish like salmon contain high levels of omega-3 fatty acids, which are valuable to your health, as well as your developing baby’s. 

According to the American Pregnancy Association, eating low-mercury fish or taking fish oil capsules can boost your mental health and promote the development of your baby’s neurological system. Additionally, high-quality brands of fish oil are usually tested for mercury contamination.

If high-mercury fish is a new concept for you and you’ve just realized you’ve eaten a tuna sandwich every day for the past year, don’t panic. If you’re not experiencing any symptoms related to mercury exposure, there’s a good chance that your body isn’t struggling with mercury poisoning. If you’re concerned about your health, though, or if you’re pregnant, talk to your doctor about having your mercury levels tested.

If you do not feel well, there’s a chance that you’re feeling bad because of eating high-mercury fish, but there also may be another reason for your illness, so seek out proper testing before self-diagnosing mercury poisoning. Many of the remedies you see online may not be accurate or helpful, so self-diagnosing can put your health at risk or cause you to overlook another condition. It is better to consult with a doctor about your symptoms.

You might be vigilant about your diet, but are you aware that mercury could exist elsewhere in your environment? Elemental mercury can be especially dangerous because you can’t smell, taste, or see it after it evaporates. Breathing mercury vapors is even more dangerous than swallowing mercury, so consider the following sources of mercury that you could have in your home:

• Older thermometers 
• Jewelry imported from another country
• Silver fillings in your teeth (these might be up to 50% mercury)
• Skin-lightening products

Thimerosal, which is a preservative found in vaccines, also contains mercury. Some people are worried that vaccines cause autism and other developmental disabilities. However, there is no substantial evidence to support this, and thimerosal is considered safe for most people. Current studies have shown that there is no link between thimerosal and autism, but if you’re concerned, there are many thimerosal-free vaccine formulations available for both children and adults.

Mercury toxicity can be very serious. It’s rare for adults to experience mercury poisoning simply from their diet, but that risk is much higher for unborn babies and small children. 

Make an appointment with your primary care provider if you suspect that you’ve eaten too much mercury or you’re concerned about your child’s health. Your physician will be able to recommend alternative foods and determine whether you should undergo any type of treatment for mercury poisoning.