Choosing Wisely: Which fish have the least heavy metals?

According to the U.S. Food and Drug Administration (FDA), many fish provide critical nutrients like omega-3 fatty acids, but some varieties accumulate more methylmercury and other heavy metals than others. To maximize health benefits while minimizing risk, it's essential to understand which fish have the least heavy metals and why.

Quick Summary

This article outlines the fish with the lowest levels of heavy metals, including mercury, and explains the bioaccumulation process. It provides recommendations for safe seafood consumption, highlighting options that are rich in nutrients while being low in contaminants.

Key Points

• Choose Small, Short-Lived Fish: Smaller fish like sardines, anchovies, and Atlantic mackerel accumulate the least heavy metals because they are lower on the food chain and have shorter lifespans.

• Favor Farmed Trout and Wild-Caught Salmon: Both farmed rainbow trout and wild-caught salmon are consistently low in mercury and excellent sources of omega-3s.

• Don't Fear Shellfish: Most shellfish, including shrimp, oysters, and scallops, are very low in mercury and are safe, nutrient-dense choices.

• Limit Large Predators: High-trophic-level fish like shark, swordfish, and king mackerel should be limited or avoided, especially for vulnerable populations, due to high heavy metal accumulation.

• Diversify Your Choices: Eating a variety of low-mercury seafood reduces exposure to any single contaminant, ensuring a balanced intake of nutrients.

• Consider Official Guidelines: Reputable organizations like the FDA provide valuable advice on safe fish consumption frequencies based on species and population.

Understanding Heavy Metal Bioaccumulation

Heavy metals, particularly mercury, exist naturally in the environment and are released into water bodies through natural processes and industrial pollution. Once in the water, microorganisms convert mercury into a more toxic form called methylmercury. This methylmercury is absorbed by small aquatic organisms and accumulates up the food chain, a process known as biomagnification.

Larger, predatory fish that live longer are at the top of this food chain and consume many smaller, contaminated fish over their lifespan. This is why species like shark and swordfish have significantly higher concentrations of mercury compared to smaller, shorter-lived fish like sardines and anchovies. By choosing fish lower on the food chain, consumers can greatly reduce their exposure to these contaminants.

Best Fish with the Least Heavy Metals

To make the healthiest choices, opt for fish that are small, reproduce quickly, and have a short lifespan. These species don't have enough time to accumulate significant levels of heavy metals.

Low-Mercury Fish Options

• Wild-Caught Salmon: Both fresh and canned wild salmon are consistently low in mercury and packed with omega-3s. Alaskan salmon is particularly noted for its well-managed fisheries.
• Sardines: These tiny, oily fish are not only low in heavy metals but are also excellent sources of calcium and omega-3s, as you can consume the entire fish, including the bones.
• Rainbow Trout: U.S.-farmed rainbow trout is a highly sustainable option with low contaminant levels.
• Atlantic Mackerel (Smaller): This smaller variety of mackerel is a great source of omega-3s and is low in mercury. It is important to distinguish it from the high-mercury King mackerel.
• Anchovies: A small forage fish, anchovies are a very safe bet and provide a concentrated dose of omega-3 fatty acids.
• Tilapia: Farmed tilapia is a popular, low-mercury fish that is also a good source of lean protein.
• Cod: This flaky white fish is consistently recommended for its low mercury content and provides a solid source of protein.
• Catfish: Often farm-raised, catfish is another low-mercury option.

Safe Shellfish Choices

Shellfish are generally low in mercury and are a safe addition to a healthy diet. This is because they are low on the food chain and are filter feeders rather than predators.

• Shrimp: One of the most popular seafood options, shrimp are very low in mercury.
• Oysters and Scallops: As bivalves, oysters and scallops are among the lowest seafood options for heavy metal accumulation.
• Clams and Mussels: Similar to oysters, these filter feeders pose a minimal heavy metal risk.

Comparing Low-Mercury vs. High-Mercury Seafood

To illustrate the difference, here is a comparison of typical seafood choices. Note that mercury levels can vary by fish size, age, and catch location. The values provided are average estimations.

Feature	Low-Mercury Options (e.g., Sardines, Salmon)	High-Mercury Options (e.g., Shark, Swordfish)
Trophic Level	Low	High
Toxicity Risk	Low to Very Low	High
Typical Size	Small	Large
Lifespan	Short	Long
Consumption Frequency	Recommended 2-3 times per week or more	Limit to no more than once or twice a month, or avoid
Avg. Mercury (ppm)	<0.1	>0.5

Which Fish to Limit or Avoid

Some fish should be consumed in limited quantities or avoided entirely, especially by pregnant women and young children, due to their high mercury content.

• Shark: A large predator at the top of the food chain with very high mercury levels.
• Swordfish: Known for high mercury accumulation due to its size and predatory diet.
• King Mackerel: Larger and longer-lived than smaller Atlantic mackerel, with higher mercury levels.
• Bigeye Tuna: This large tuna species has significantly higher mercury than canned light (skipjack) tuna.
• Marlin: Similar to swordfish, marlin is a large predator with high mercury content.
• Orange Roughy: A long-lived, deep-sea fish with a reputation for accumulating high levels of mercury.
• Tilefish (Gulf of Mexico): This specific variety has very high mercury levels, whereas Tilefish from the Atlantic is considered a better choice.

Considering Farmed vs. Wild-Caught Fish

The debate between farmed and wild-caught fish is complex regarding heavy metals. Farmed fish are raised in controlled environments, which often results in lower mercury levels compared to their wild counterparts, particularly for species prone to high accumulation in the wild. However, other contaminants like PCBs and the use of antibiotics in some operations are potential concerns with farmed fish. Conversely, wild-caught fish can have higher mercury levels but offer other benefits, such as leaner meat and potentially different omega-3 profiles depending on their diet. For the safest options, consider sourcing recommendations from reputable organizations like the Monterey Bay Aquarium Seafood Watch, which evaluates both sustainability and contaminant levels. For most low-mercury species like salmon, both farmed and wild are safe bets.

Beyond Mercury: Other Heavy Metals

While mercury is the most widely discussed heavy metal in seafood, others like cadmium, lead, and arsenic can also be present. Seafood is generally not the primary source of exposure to these metals for most people. However, certain shellfish, which are bottom-feeders, can sometimes accumulate higher levels of cadmium or arsenic. Industrial pollution in specific waterways can also elevate local contamination levels. By diversifying your seafood intake and choosing from monitored, safe sources, you can minimize your risk from these metals as well.

Conclusion: Making Informed Seafood Choices

Fish remains an excellent source of nutrients, and the key to safe consumption is making informed decisions. To keep heavy metal intake low, prioritize smaller, shorter-lived, and lower-trophic-level fish like salmon, sardines, and trout, as well as most shellfish. Limit or avoid large predatory species such as shark, swordfish, and king mackerel. By diversifying your seafood choices and paying attention to official guidelines, you can safely enjoy the significant health benefits that fish offers. For the most comprehensive and up-to-date guidance, refer to the FDA's advice about eating fish.

Resources for Safe Seafood

• Monterey Bay Aquarium Seafood Watch: Provides recommendations on sustainable and healthy seafood choices.
• Environmental Defense Fund (EDF): Offers a consumer guide ranking fish by mercury levels.
• Local Advisories: Always check for specific local advisories if you consume fish caught from local waters.

Frequently Asked Questions

Why do some fish have more heavy metals than others?

Larger, predatory fish at the top of the food chain accumulate more heavy metals, especially mercury, through a process called biomagnification. They consume many smaller fish over a longer lifespan, concentrating the metals in their tissue.

Is canned tuna high in mercury?

Canned 'light' tuna, which typically includes smaller skipjack tuna, is considered a 'Best Choice' with significantly lower mercury levels than canned or fresh/frozen albacore or bigeye tuna.

Can cooking fish remove mercury?

No, cooking methods like frying, grilling, or poaching do not reduce the amount of mercury in fish. The metal is tightly bound to the fish's muscle tissue.

Are farmed fish safer from heavy metals than wild-caught?

Generally, farmed fish raised in controlled environments, like rainbow trout, have lower mercury levels than some wild species. However, it is important to consider farming practices, including sustainability and other potential contaminants.

What is the safest fish for pregnant women and children?

The FDA recommends that pregnant women and children consume 2-3 servings per week from the 'Best Choices' list, which includes fish very low in mercury like salmon, sardines, and trout.

How can I check the mercury levels of different fish species?

The FDA and EPA provide a combined list detailing which fish fall into the 'Best Choices,' 'Good Choices,' and 'Choices to Avoid' categories based on their mercury content.

Is it safe to eat shellfish regarding heavy metals?

Yes, most shellfish like shrimp, scallops, and oysters are very low in mercury. While some can accumulate other metals like cadmium, they are generally considered safe for regular consumption.