What is the most unhealthy fish to eat in the world?

October 25, 2025 •

3 min read

According to the FDA, certain fish like shark, swordfish, and Gulf of Mexico tilefish are on the 'Choices to Avoid' list due to high mercury levels. Determining what is the most unhealthy fish to eat in the world involves examining factors like mercury accumulation, environmental contaminants, and farming methods that can compromise nutritional value and safety.

Quick Summary

This guide examines factors determining the unhealthiest fish, including high mercury content in large predators, contaminants in farmed species, and poor omega-fatty acid ratios. It helps readers make safer seafood choices.

Key Points

High Mercury Fish: Large, predatory species like shark, swordfish, and certain tilefish contain the highest levels of mercury due to biomagnification.
Farmed vs. Wild: Some farmed fish, such as Atlantic salmon and tilapia, may have less favorable nutritional profiles or higher contaminant levels compared to their wild counterparts.
Contaminants Beyond Mercury: PCBs, dioxins, and pesticides are other pollutants found in some fish, which accumulate in fatty tissue and can pose long-term health risks.
Risk Groups: Pregnant women, young children, and nursing mothers should be particularly cautious about high-mercury fish due to potential harm to the developing brain and nervous system.
Informed Choices: Opting for smaller, low-mercury, wild-caught fish and diversifying your seafood intake is the safest approach to minimize health risks while enjoying fish's benefits.

Understanding the Most Unhealthy Fish

When evaluating what is the most unhealthy fish to eat in the world, multiple factors come into play beyond a single species. While certain fish are universally considered high-risk due to their toxicity, a complete answer also accounts for predatory position, farming conditions, and potential for environmental pollutants. The danger often stems from biomagnification, where toxins like mercury accumulate and become more concentrated as they move up the food chain. Apex predators and larger, longer-living fish are prime examples of this phenomenon.

The Apex Predators: High Mercury Levels

Several large, predatory fish are consistently cited as the unhealthiest options due to their exceptionally high mercury content. Mercury exposure, especially in the form of methylmercury found in fish, can lead to serious neurological damage.

Shark: As the ultimate ocean predator, sharks sit at the top of the food chain, accumulating massive amounts of mercury over their long lifespans. This makes them one of the most toxic choices. For the same reason, the FDA advises against their consumption, particularly for pregnant women and young children.
Swordfish: Another large, predatory species, swordfish have consistently high levels of mercury. The FDA and other health organizations recommend limiting intake due to this contamination.
King Mackerel: While smaller than sharks or swordfish, certain varieties of king mackerel also contain significant mercury levels, placing them on the list of fish to avoid or limit.
Tilefish (from the Gulf of Mexico): This specific type of tilefish contains notoriously high levels of mercury, earning it a 'Choice to Avoid' label from the FDA.

The Issues with Farmed Fish

While wild-caught fish often contain environmental contaminants, certain farmed fish can present a different set of health concerns. The crowded, artificial conditions of many fish farms can lead to stressed animals, poor nutrition, and higher levels of pollutants and additives.

Farmed Atlantic Salmon: The vast majority of Atlantic salmon available is farmed due to the species being endangered. These fish are often raised in crowded, unsanitary conditions and fed unnatural diets, which can result in higher saturated fat content and a less favorable omega-3 to omega-6 ratio compared to wild salmon. Some farmed salmon are also given chemicals to improve color.
Tilapia: While not a predatory fish, farmed tilapia has been singled out for its less desirable omega-fatty acid profile. It contains relatively low levels of heart-healthy omega-3s and high levels of omega-6s, which can be pro-inflammatory when consumed in high amounts.

The Role of Environmental Pollutants

Beyond mercury, fish can be contaminated with a host of other harmful chemicals. These include Polychlorinated Biphenyls (PCBs), dioxins, and pesticides. These fat-soluble chemicals can accumulate in a fish's fatty tissue over time, and a diet high in contaminated fish can lead to accumulation in humans. This makes larger, longer-lived fish, both wild and farmed, more likely to carry a significant chemical load.

Comparison of High-Risk Fish Species


Fish Species	Primary Health Concern	Mercury Level (Example)	Other Contaminants	Notes
Shark	Very High Mercury	~0.979 ppm (Average)	PCBs, Dioxins	Apex predator; long-lived; highest bioaccumulation risk.
Swordfish	Very High Mercury	~0.995 ppm (Average)	PCBs, Dioxins	High mercury makes it a frequent 'avoid' recommendation.
Tilefish (Gulf)	Very High Mercury	~1.123 ppm (Average)	PCBs, Dioxins	Specific geographic population has particularly high mercury levels.
Farmed Atlantic Salmon	Poor Nutritional Profile, PCBs	Low-Moderate	PCBs, Antibiotics	Unfavorable omega-3 to omega-6 ratio; crowded conditions.
Tilapia	Poor Nutritional Profile	Low	Possible contaminants in farmed variety	Contains low omega-3s and high omega-6s, potentially increasing heart disease risk.

Authoritative Outbound Link

For detailed information on current seafood safety guidelines and a comprehensive list of fish to eat and avoid, consult the U.S. Food and Drug Administration's 'Advice about Eating Fish'.

Conclusion: Making Smarter Seafood Choices

While identifying a single "most unhealthy fish" is complex, species like shark, swordfish, and specific types of tilefish consistently rank highest in terms of mercury content and should be avoided or severely limited, especially by at-risk groups like pregnant women and children. Concerns also exist for some farmed species, such as Atlantic salmon and tilapia, due to less favorable nutritional content and potential contaminant exposure from farming practices. The ultimate takeaway is that consumers should be mindful of a fish's position in the food chain and its source. Choosing smaller, wild-caught fish, and a variety of seafood, is generally a safer strategy to enjoy the benefits of fish without the elevated health risks. Informed decisions are key to navigating the complex landscape of seafood consumption safely.

Frequently Asked Questions

Shark is considered one of the unhealthiest fish to eat because it is an apex predator that lives a long time, leading to a high accumulation of mercury in its tissues through a process called biomagnification.

Yes, some farmed fish can pose health risks. Concerns include exposure to antibiotics, a less beneficial omega-3 to omega-6 fatty acid ratio due to unnatural diets, and potential contamination from the crowded, enclosed environment.

Biomagnification is the process by which a substance, such as mercury, increases in concentration as it moves up the food chain. This means that large, predatory fish that eat smaller contaminated fish will have higher levels of the toxin, making them riskier to consume.

Tilefish from the Gulf of Mexico is particularly unhealthy due to its very high mercury content, which has led the FDA to place it on its 'Choices to Avoid' list. Atlantic tilefish typically has lower levels.

No, pregnant women and children do not need to avoid all fish. However, they should strictly limit or avoid high-mercury species like shark and swordfish. They should instead choose low-mercury options, such as salmon and sardines, following specific consumption guidelines.

Yes, other contaminants found in some fish include Polychlorinated Biphenyls (PCBs), dioxins, and pesticides. These chemicals can accumulate in the fatty tissues of fish and may pose health risks when consumed.

To minimize risks, consider healthier alternatives like wild-caught salmon, sardines, and trout, which are typically low in mercury and rich in beneficial omega-3 fatty acids. It's also recommended to vary the types of fish consumed.