What's the most unhealthy fish to eat?

October 6, 2025 •

3 min read

According to the U.S. FDA, large, predatory fish like shark, swordfish, and king mackerel are on the "Choices to Avoid" list due to their high mercury content. While fish offers numerous health benefits, certain varieties pose risks due to high levels of contaminants, unsustainable farming, or poor nutritional balance. Knowing what's the most unhealthy fish to eat can help you make informed decisions for your health and the environment.

Quick Summary

Several fish species are considered unhealthy due to high mercury levels, contaminants from poor farming practices, and unsustainable sourcing. Understanding the risks associated with certain fish, including large predators and some farmed varieties, is key to making better nutritional and environmental choices.

Key Points

Avoid high-mercury predators: Large, long-lived predatory fish like shark, swordfish, and king mackerel are the most unhealthy due to high mercury accumulation.
Beware of poor farming practices: Some farmed fish, especially imported tilapia and swai, are associated with contaminants like antibiotics and bacteria due to unsustainable and unhygienic conditions.
Know the nutritional trade-offs: While some farmed fish may have higher omega-3s, others, like tilapia, have a less favorable omega-6 to omega-3 ratio due to their feed.
Check the origin: The country of origin and farming regulations significantly impact a fish's safety; look for certification labels like MSC or consult the Seafood Watch guide.
Choose healthier alternatives: Opt for low-mercury, sustainable options such as salmon, sardines, farmed U.S. catfish, and light canned tuna to enjoy fish's benefits safely.
Vulnerable groups need special care: Pregnant women, nursing mothers, and young children should be extra cautious about high-mercury fish due to increased sensitivity to neurological damage.
Not all wild fish are created equal: Not all wild fish are safe, as some can have high mercury levels or are unsustainably caught; check local advisories.
Cooking doesn't remove mercury: Common cooking methods do not reduce the mercury content in fish because it is bound to the muscle tissue.

Navigating the Dangers of Unhealthy Fish

While fish is generally a cornerstone of a healthy diet, rich in lean protein and omega-3 fatty acids, not all fish are created equal. Research indicates specific fish should be limited or avoided due to high levels of neurotoxins like mercury, pollutants such as PCBs and dioxins, or problematic farming methods. This guide explores which fish are considered unhealthy and why.

The Mercury Menace: Large, Predatory Fish

High mercury content is a major health risk in certain fish. Methylmercury, a neurotoxin, builds up in the food chain. Large, predatory fish consume smaller fish and accumulate higher concentrations of mercury. The FDA and EPA advise certain groups, such as pregnant women, to avoid these high-mercury species.

Swordfish: Known for high mercury levels.
Shark: Apex predators with very high mercury levels.
King Mackerel: High in mercury and should be limited.
Tilefish (from the Gulf of Mexico): Consistently high in mercury and on the FDA/EPA's "Choices to Avoid" list.
Bigeye Tuna: Higher mercury than canned light tuna.
Orange Roughy: A long-lived fish that accumulates high mercury.

Problematic Farmed Fish

Some farming practices raise concerns about the safety and nutrition of fish. Issues include contamination and poor nutrition from unnatural diets.

Tilapia from China: Concerns exist regarding farming practices in some regions of China, including the use of animal waste as feed, potentially increasing bacterial contamination. Farmed tilapia can also have an unfavorable omega-6 to omega-3 ratio.
Swai Fish (Pangasius): Often farmed in overcrowded conditions in Vietnam, with concerns about poor water quality and antibiotic use.

Wild vs. Farmed Fish: A Comparison

The health and contaminant levels of fish vary depending on if they are wild or farmed, but the source and methods are key.


Feature	Wild-Caught Fish	Farm-Raised Fish	Considerations
Diet	Natural diet.	Processed feed.	Natural diet can mean better nutrition in wild fish.
Omega-3s	Often lower total fat, but rich in omega-3s.	Can be higher in omega-3s with fortified feed, but also higher in omega-6s.	Some farmed fish may have a less favorable omega-6 to omega-3 ratio.
Contaminants	Can have mercury and pollutants based on location.	Lower mercury in some species, but potentially higher PCBs/dioxins based on feed/conditions.	Origin is important; regulated farms may be safer.
Sustainability	Risk of overfishing.	Varies widely from sustainable to damaging.	Look for certifications like MSC or Seafood Watch.

Making Healthier Seafood Choices

Making healthy fish choices involves considering mercury, sourcing, and farming. The benefits of eating fish often outweigh the risks when choosing a variety of lower-mercury options and cooking properly.

Consult resources like the FDA's guidelines or the Monterey Bay Aquarium's Seafood Watch for information on healthy and sustainable options. Informed choices allow you to enjoy seafood's benefits while minimizing risks to health and the environment.

What are some examples of healthier fish options?

Consider low-mercury, sustainably-sourced options:

Salmon: Excellent for omega-3s.
Sardines: Low-mercury, omega-3 rich, sustainable.
Anchovies: Small, low-mercury, nutrient-dense.
Catfish (U.S. Farmed): Responsibly farmed, low in contaminants.
Light Canned Tuna: Skipjack tuna is lower in mercury than albacore.

Conclusion

To answer what's the most unhealthy fish to eat?, the primary concerns are large, predatory fish with high mercury, including shark, swordfish, Gulf of Mexico tilefish, king mackerel, bigeye tuna, and orange roughy. Additionally, some poorly managed farmed fish, particularly imported varieties from regions with less oversight, can pose risks due to contamination. Choosing smaller, low-mercury fish and responsibly sourced seafood helps you benefit from fish while reducing exposure to harmful contaminants and supporting sustainable practices.

Frequently Asked Questions

The fish with the highest mercury content are typically large, predatory species like shark, swordfish, king mackerel, and Gulf of Mexico tilefish. They accumulate high levels of mercury by consuming smaller, mercury-contaminated fish throughout their long lives.

Tilapia's health depends heavily on its sourcing. While a good source of lean protein, some imported farmed tilapia, especially from China, has been linked to concerning practices, such as feeding the fish animal waste. Choosing responsibly farmed tilapia from regions with stricter regulations, like the U.S. or Peru, is a safer option.

Not necessarily. The healthiness depends more on the specific species, location, and farming practices than whether it's wild or farmed. For example, some farm-raised fish are lower in mercury than their wild counterparts because they are not exposed to polluted environments. However, certain farming methods can lead to higher levels of other pollutants.

The biggest health risk associated with unhealthy fish is high mercury exposure. Methylmercury can cause neurological damage and is especially harmful to the developing brains of fetuses, infants, and young children.

You can check for certifications on product labels from organizations like the Marine Stewardship Council (MSC). Online resources, such as the Monterey Bay Aquarium's Seafood Watch guide, also provide up-to-date recommendations based on both health and sustainability factors.

No, cooking fish does not reduce its mercury content. Mercury is bound to the proteins in the fish's muscle tissue, so methods like frying, grilling, or poaching have no effect on the overall mercury concentration.

Some of the healthiest fish options are low in mercury and high in beneficial omega-3s. Excellent choices include salmon (wild or farmed), sardines, anchovies, and U.S.-farmed catfish.