What is the lowest quality fish?

January 12, 2026 •

5 min read

According to the National Resources Defense Council (NRDC), certain large, predatory fish like king mackerel, shark, and tilefish contain high levels of mercury, making them among the lowest quality fish options. Low quality can stem from various factors, including high contaminant levels, poor nutritional value, and unsustainable or unsanitary farming practices.

Quick Summary

Several factors define low-quality fish, including high mercury and contaminant levels, poor nutrition, and damaging farming methods. Examples include high-mercury predators and fish from unsanitary farms like certain tilapia and farmed salmon. Consumers should consider sourcing and certifications to make healthy, responsible seafood choices.

Key Points

High Mercury Content: The lowest quality fish often includes large, predatory species like shark and swordfish, which accumulate high levels of neurotoxic mercury.
Unsanitary Farming Conditions: Poor quality is often linked to fish from overcrowded, uncertified farms (e.g., some tilapia and shrimp) where unsanitary conditions lead to chemical and antibiotic use.
Poor Nutritional Profile: Some low-quality farmed fish, like certain tilapia, have an unbalanced omega-6 to omega-3 fatty acid ratio, diminishing their nutritional value.
Sustainability Concerns: Overfished species such as orange roughy and Chilean sea bass are considered low quality due to severe ecological impact, regardless of other factors.
Signs of Freshness: Freshness is a key quality indicator; low-quality fish often has cloudy eyes, a strong 'fishy' smell, and mushy flesh, indicating age and poor handling.

Defining low quality fish

Low quality in fish is not solely based on taste but on a combination of factors related to health, environmental impact, and nutritional value. Understanding these aspects allows consumers to make healthier, more responsible choices at the seafood counter.

Mercury and Contaminants

One of the most significant indicators of poor fish quality is a high concentration of mercury and other chemical contaminants. Mercury bioaccumulates in the food chain, meaning predators at the top accumulate higher concentrations. The US FDA warns against consuming certain species with excessive levels, especially for pregnant women and young children.

Farming practices

Some farmed fish have gained a reputation for low quality due to the conditions in which they are raised. Overcrowded fish pens can lead to the spread of disease, necessitating the heavy use of antibiotics and pesticides. In some instances, unsanitary farming practices have resulted in fish with higher levels of contaminants.

Poor nutritional profiles

While many types of fish are celebrated for their omega-3 fatty acids, some species offer a less favorable nutritional profile. For example, studies have shown that some farmed tilapia can have an unfavorable ratio of omega-6 to omega-3 fatty acids, which is less healthy. The diet provided to farmed fish often influences this balance, potentially making them a lower-quality nutritional choice compared to wild-caught counterparts.

Low quality fish examples

Shark and Swordfish

As apex predators, sharks accumulate high levels of mercury, making them a consistently low-quality option from a health perspective. Swordfish also contains high mercury levels, posing a health risk, especially for vulnerable populations. The long lifespan of these fish means more time for toxins to build up in their flesh.

Orange Roughy

This long-lived deep-sea fish, also known as a slimehead, can live for over 100 years. Due to its longevity, it has a high capacity to accumulate mercury and is often associated with unsustainable harvesting practices. Most orange roughy on the market today is considered unsustainable.

Farmed Tilapia

Often sold as an inexpensive, mild-flavored fish, much of the farmed tilapia sold globally is viewed as low quality. Concerns include unsustainable farming practices, reliance on antibiotics and chemicals in crowded conditions, and a poor omega-6 to omega-3 fatty acid ratio. Consumers are advised to check the fish's origin, with tilapia from China often cited as a higher-risk option.

Atlantic Farmed Salmon

While many farmed salmon are raised responsibly, some practices have contributed to low-quality perceptions. The use of certain feeds and the potential for contaminants in some crowded fish pens have raised concerns among some consumers. Choosing certified, sustainably sourced farmed salmon or wild-caught alternatives can mitigate these issues.

Chilean Sea Bass

Another long-lived fish, the Patagonian toothfish (marketed as Chilean sea bass), has been heavily overfished and often contains high levels of mercury. Due to unsustainable fishing practices and high contaminant levels, it is frequently listed as a fish to avoid.

Comparison: High vs. Low Quality Fish


Attribute	Low Quality Fish (Examples: Shark, Orange Roughy)	High Quality Fish (Examples: Wild Salmon, Sardines)
Contaminants	High levels of mercury and other pollutants.	Typically low levels of mercury and contaminants.
Sustainability	Often linked to overfishing, habitat destruction, or problematic farming.	Harvested using responsible, sustainable practices.
Nutritional Profile	Can have poor omega-6 to omega-3 ratio; lower overall nutritional density.	High in beneficial omega-3 fatty acids (EPA, DHA) and other nutrients.
Health Risks	Higher risk of mercury poisoning and other toxic effects with regular consumption.	Lower health risks from contaminants, offering significant health benefits.
Flavor and Texture	Can vary widely, but sometimes described as less desirable or mushy, depending on the source.	Often prized for robust flavor and firm texture.
Source/Origin	Often sourced from questionable farming or fishing operations.	Sourced from clean, well-managed wild fisheries or certified farms.

Consumer guidelines for choosing high-quality fish

To avoid the lowest quality fish, consumers can follow several guidelines and look for specific indicators when purchasing seafood. These tips help ensure a healthier, more sustainable choice.

Prioritize Wild-Caught or Certified Farmed: While not all farmed fish is low quality, looking for third-party certifications like the Aquaculture Stewardship Council (ASC) or Best Aquaculture Practices (BAP) ensures responsible methods were used. Wild-caught fish from well-managed fisheries is also a great option. NOAA Fisheries provides useful guidelines for sustainable seafood.
Consider the Source: For fish like tilapia and farmed shrimp, the country of origin is important. Some sources, particularly from Southeast Asia, have been associated with lower quality standards. Asking your grocer about the source can provide key information.
Check for Freshness Indicators: When buying fresh fish, sensory clues are important. Fresh fish should not have a strong "fishy" odor but should smell clean like the sea. Look for clear, plump eyes and firm, shiny skin.
Avoid High-Mercury Predators: Steer clear of the largest predatory fish, which consistently carry the highest mercury burden. The NRDC recommends avoiding king mackerel, marlin, shark, swordfish, and bigeye tuna, especially for at-risk individuals.
Eat Lower on the Food Chain: Smaller fish like sardines, anchovies, and Atlantic mackerel are not only nutrient-dense but also accumulate less mercury and are more sustainable.

Conclusion

Identifying the lowest quality fish involves considering health risks, ethical sourcing, and nutritional content. Highly predatory fish like shark and swordfish pose risks due to high mercury levels, while species like some farmed tilapia raise concerns over farming practices and nutritional imbalances. Making informed choices by prioritizing wild-caught or certified farmed seafood, checking for freshness, and being mindful of fish sourcing empowers consumers to choose healthier, more responsible options for both themselves and the planet.

Consider sustainability: Always check for sustainability certifications or choose fish recommended by trusted organizations like Seafood Watch.
Be aware of mercury: Smaller fish lower on the food chain, such as sardines and salmon, generally have lower mercury levels.
Avoid controversial farming practices: Steer clear of fish from unsanitary or uncertified farms that overuse antibiotics and chemicals.
Look for signs of freshness: The best fish is firm to the touch with clear eyes and a clean scent.
Diverse your choices: Eating a variety of low-mercury, sustainable fish can provide a wide range of nutritional benefits.

Frequently Asked Questions

The dirtiest or unhealthiest fish to eat typically have high levels of mercury (such as shark, king mackerel, and swordfish) or are raised in unsanitary farmed conditions that require heavy antibiotic use (such as some imported tilapia and shrimp).

The quality of farmed tilapia varies significantly by origin. While some farms produce good quality fish, sources from places like China are often associated with poor farming practices, a high omega-6 content, and potential antibiotic exposure, making them a riskier choice.

Orange roughy, a very long-lived species, has accumulated high levels of mercury over its lifetime. It has also been heavily overfished, making it a poor choice from both a health and sustainability perspective.

Not all farmed salmon is lower quality; responsible, certified aquaculture produces nutritious fish. However, some farms use feeds that result in a different nutritional profile, and overcrowding can raise concerns about antibiotics and contaminants. Look for sustainable certifications.

Good, low-mercury alternatives include smaller fish like sardines, anchovies, and wild-caught salmon. Other safe choices are catfish, flounder, and pollock, especially when sourced responsibly.

High-quality fish is generally fresh, sustainably sourced (wild or certified farmed), low in contaminants like mercury, and high in beneficial nutrients, especially omega-3s. Low-quality fish often fails these standards due to pollution, poor handling, or unsustainable harvesting.

Fresh, high-quality fish has clear, plump eyes, firm flesh that springs back when touched, and a clean, mild, sea-like smell. Poor quality fish will have cloudy or sunken eyes, mushy flesh, and a strong, unpleasant fishy odor.