Nutrition Diet: What fish are not contaminated? Your guide to safer seafood

October 15, 2025 •

4 min read

According to the U.S. FDA, larger, long-lived predatory fish tend to accumulate higher levels of environmental contaminants like mercury. This makes it crucial to understand what fish are not contaminated to make safer and more informed dietary choices. This guide will provide the knowledge you need to select the healthiest options for your family.

Quick Summary

This guide explains the sources of seafood contamination, detailing why smaller fish are often safer and which specific species are known to have low levels of toxins. It covers sustainable practices and offers practical advice for choosing nutritious, low-mercury options.

Key Points

Choose Low on the Food Chain: Prioritize smaller, shorter-lived fish like sardines, anchovies, and mackerel to minimize mercury accumulation.
Diversify Your Seafood: Eat a variety of fish and shellfish to reduce exposure to any single type of contaminant.
Opt for Wild Alaskan Fish: Wild-caught salmon from Alaska is consistently cited for its low contaminant levels due to well-managed fisheries.
Look for Certifications: Seek out seals like the Marine Stewardship Council (MSC) and check guides like the Monterey Bay Aquarium’s Seafood Watch for sustainable options.
Favor U.S. Farmed Fish: Domestic farmed fish, particularly those from closed recirculating systems like rainbow trout, are often better regulated and have lower contaminant levels.
Monitor Consumption of High-Mercury Fish: Limit or avoid consumption of large predatory fish such as king mackerel, shark, and swordfish, especially for sensitive populations like pregnant women and children.

Understanding the Sources of Contamination

Fish can accumulate contaminants from their environment, primarily through the water they live in and the food they eat. The two main concerns are mercury and a class of chemicals called persistent organic pollutants (POPs), which include polychlorinated biphenyls (PCBs) and PFAS (per- and polyfluoroalkyl substances). Microplastics have also been identified as a growing concern in aquatic environments.

Mercury and the Food Chain

Mercury contamination is a natural phenomenon exacerbated by industrial pollution. When mercury enters waterways, bacteria convert it into a highly toxic form called methylmercury. This methylmercury builds up in fish, and the levels increase as you move up the food chain, a process known as biomagnification. Large predatory fish, such as sharks, swordfish, and king mackerel, are at the top of this chain and therefore have the highest mercury concentrations. Smaller, short-lived fish contain significantly lower amounts of mercury, making them a safer option.

PCBs and other Environmental Toxins

PCBs are human-made chemicals that persist in the environment and accumulate in the fatty tissues of animals. While their use has been banned, they remain present in some waterways. PCBs and other legacy pollutants are a concern, particularly in certain freshwater fish. Choosing fish that are low on the food chain and sourced from well-managed waters can minimize exposure.

The Safest Fish Choices: Low Contamination Options

When choosing fish for your diet, prioritize smaller, short-lived species and those from well-regulated fisheries. Here is a list of fish and shellfish that are consistently recommended as low in contaminants by health and environmental organizations:

Wild Alaskan Salmon: Well-managed Alaskan fisheries produce wild salmon with some of the lowest levels of contaminants. They are also rich in healthy omega-3 fatty acids.
Sardines and Anchovies: These tiny, oily fish are very low on the food chain and are a nutritional powerhouse, providing high amounts of omega-3s, calcium, and vitamin D.
Rainbow Trout (farmed in the U.S.): U.S. farm-raised trout is a sustainable choice with low contaminant levels, especially when raised in closed recirculating systems.
Atlantic Mackerel (Chub): Unlike king mackerel, the smaller Atlantic and Pacific chub mackerel are considered a good choice with low mercury levels.
Cod: Often cited as a low-mercury option, cod is a lean protein source that can be enjoyed regularly.
Shrimp: Most shrimp consumed in the U.S. have low mercury levels and are a safe seafood choice.
Oysters and Mussels: Bivalves like oysters and mussels are filter feeders and are low in contaminants, making them an excellent choice for a sustainable and healthy diet.
Tilapia (farmed): Farmed tilapia is a low-mercury, low-fat fish. It is widely available and can be part of a healthy diet.

Sourcing and Certifications for Safer Seafood

Beyond choosing the right species, where and how a fish was caught or farmed can also impact its contaminant levels and environmental footprint. Looking for specific certifications and regional sources can help you make a better choice.

Wild-Caught from Regulated Areas: Wild-caught fish from well-managed fisheries, like those in Alaska, are often a safer bet. Alaska has strict regulations to ensure the health of its seafood populations and the waters they inhabit.
U.S. Farmed Fish: Many U.S. fish farms, particularly those using closed systems, have tighter regulations on water quality and feed than international operations, resulting in lower contaminant levels.
Marine Stewardship Council (MSC): The MSC is an independent certification organization that verifies fisheries meet sustainability standards. While not a guarantee of zero contamination, it is an indicator of responsible practices.
Monterey Bay Aquarium's Seafood Watch: This guide provides recommendations on seafood based on environmental and sustainability factors. It's a useful tool for making informed choices at the store or in restaurants.

High-Mercury vs. Low-Mercury Fish

To help visualize the difference, this table compares common high-mercury and low-mercury fish based on FDA and other health advisories:


Feature	High-Mercury Fish	Low-Mercury Fish
Examples	King Mackerel, Shark, Swordfish, Bigeye Tuna, Tilefish (Gulf of Mexico)	Salmon (Wild-caught), Sardines, Anchovies, Cod, Shrimp, Tilapia
Food Chain Position	Apex predators, highest level of the food chain	Low on the food chain, smaller and shorter-lived
Mercury Accumulation	Highest due to biomagnification	Lowest, with minimal accumulation
Recommended Consumption	Infrequent or limited, especially for pregnant women and children	Can be consumed 2-3 times per week as part of a healthy diet
Risk Factor	Higher risk of neurotoxic effects from mercury	Low risk, considered safe for regular consumption

Conclusion

Making informed choices about seafood is key to reaping the benefits of a diet rich in fish without excessive exposure to contaminants. While no fish is entirely without contaminants, focusing on smaller, short-lived species like sardines, salmon, and farmed trout can significantly reduce your risk. Diversifying your seafood intake and considering sourcing and certifications will further protect your health. Always refer to official guidance from organizations like the FDA and EPA for the latest information on safe seafood consumption for your specific needs, especially if you are pregnant, nursing, or feeding small children. For more detailed information on eating fish safely, consult the FDA's Advice about Eating Fish.

Frequently Asked Questions

Fish considered low in mercury include wild-caught Alaskan salmon, sardines, rainbow trout (farmed in the U.S.), Atlantic mackerel (chub), cod, and shrimp. These are typically smaller and have shorter lifespans, meaning they accumulate less mercury than larger, longer-lived predators.

Mercury builds up in fish through a process called biomagnification. Larger predatory fish that eat smaller fish higher up the food chain will accumulate more mercury over their longer lifespans. The higher a fish's position on the food chain, the higher its potential mercury concentration.

Not necessarily. While some farmed fish, particularly those raised in poorly regulated environments, can have issues, many U.S. farmed fish like rainbow trout and catfish are considered safe and sustainable choices. The key is to check the source and farming practices; look for fish from well-managed, closed systems.

For most individuals, health experts recommend eating two to three servings (about 8 ounces per serving) of low-mercury fish per week. Pregnant women, nursing mothers, and young children have specific guidelines and should consult advisories from organizations like the FDA and EPA.

The type of canned tuna matters. Canned light tuna (typically skipjack) has significantly lower mercury levels than canned albacore (white) tuna. Health advisories provide different consumption recommendations for each type.

Yes, many shellfish are considered very safe choices with minimal mercury and other contaminants. Filter-feeders like clams, oysters, and mussels are typically low in toxins and can be part of a healthy diet.

Reliable information can be found from government agencies such as the U.S. Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA). The Monterey Bay Aquarium's Seafood Watch guide is another excellent resource.