Fish is often praised as one of the healthiest foods you can eat. Rich in protein, omega-3 fatty acids, and essential nutrients, it supports heart and brain health. However, not all fish are equally safe. Some types—especially cheaper or poorly sourced ones—may contain harmful substances such as mercury, pollutants, or antibiotics. Knowing which fish to avoid can help protect your health and your family.

Why some fish can be dangerous

While fish is nutritious, certain species accumulate toxins from their environment. Large predatory fish, for example, often contain higher levels of mercury because they consume smaller contaminated fish.

In addition, some imported or farmed fish may be raised in polluted water or treated with chemicals and antibiotics. These factors can turn an otherwise healthy meal into a potential health risk if consumed frequently.

1. Imported farmed fish (especially catfish and shrimp)

Imported farmed fish is often one of the cheapest options in the market—but also one of the riskiest. In some countries, farming practices involve polluted water and the use of banned antibiotics.

These fish may not be strictly inspected, increasing the chance of contamination. If possible, choose locally sourced or certified products instead.

2. High-mercury fish (shark, swordfish, big tuna)

Large predatory fish are at the top of the food chain, meaning they accumulate more mercury over time.

Regular consumption of high-mercury fish can affect the nervous system, especially in children and pregnant women. Health experts recommend limiting or avoiding these species entirely.

3. Cheap tilapia and basa

Tilapia and basa are widely available and affordable, but not all sources are equal. Some farmed varieties—particularly from regions with weak regulations—may be raised in overcrowded or unsanitary conditions.

While not inherently dangerous, low-quality sources may reduce nutritional value and increase exposure to contaminants.

4. Overfished species (Atlantic cod, certain sea bass)

Some fish are not only a health concern but also an environmental one. Overfished species like Atlantic cod have struggled to recover, making them less sustainable choices.

Choosing alternative species helps protect ocean ecosystems while ensuring better quality seafood.

5. Long-lived fish like orange roughy

Orange roughy is known for its long lifespan, which allows it to accumulate toxins such as mercury over decades.

Because it matures slowly, overfishing has also significantly reduced its population, making it both a health and environmental concern.

6. Eel and other contaminated species

Eel may contain high levels of pollutants like PCBs and mercury, especially in polluted waters.

Although considered a delicacy in some cuisines, frequent consumption is not recommended due to potential long-term health risks.

Safer choices for your diet

Not all fish should be avoided. In fact, many types are extremely beneficial when chosen wisely. Smaller fish like sardines, as well as salmon and mackerel, are rich in omega-3s and generally lower in mercury.

Experts recommend eating fish regularly—but focusing on low-mercury, sustainably sourced options to maximize benefits.

Final thoughts

Fish remains a valuable part of a healthy diet, but smart choices matter. Cheap prices can sometimes hide hidden risks, from contamination to environmental concerns. By avoiding the six types of fish listed above and choosing safer alternatives, you can enjoy the benefits of seafood without compromising your health.