Three Fish Parts You Should Never Eat—One May Harm Your Kidneys

Fish is widely considered a nutritious food, providing high-quality protein and important nutrients such as omega-3 fatty acids, vitamin B12, vitamin D, selenium, and iodine. But when preparing a whole fish, many people wonder whether every part is equally safe to eat.

The answer is not necessarily.

Some fish tissues can accumulate environmental contaminants more readily than ordinary muscle meat. The risk depends heavily on the fish species, where it was caught or farmed, and the pollutants present in the environment. The U.S. FDA specifically notes that, for fish caught from certain waters, contaminants other than mercury may be concentrated in the skin, fat, and internal organs.

Here are three parts that deserve particular caution.

1. Fish intestines and other internal organs

Fish organs are sometimes used in traditional dishes, but they can be a less desirable choice when the source of the fish is uncertain.

Environmental contaminants such as PCBs and other persistent chemicals can accumulate in different tissues of fish. The U.S. Environmental Protection Agency notes that some fish-consumption advisories specifically recommend avoiding the heads, guts, liver, and reproductive organs because certain contaminants can concentrate there.

This is particularly important when eating fish caught from rivers, lakes, or coastal areas that may have contamination advisories.

If you do not know where the fish came from, eating the muscle or fillet rather than the internal organs is generally the more cautious choice.

2. Fish liver

Fish liver is especially worth mentioning because the liver plays an important role in processing substances within the body of the fish.

That does not mean every fish liver is poisonous. However, because contaminants can accumulate in internal organs, some authorities advise removing organs from recreationally caught fish before cooking. The FDA recommends removing skin, fat, and internal organs from certain locally caught fish because pollutants may accumulate in these tissues.

The concern becomes greater when the fish comes from waters affected by industrial pollution or when local consumption advisories are in place.

So, if you enjoy dishes containing fish liver, pay attention to the species and source of the fish, rather than assuming that all fish liver is equally safe.

3. Fish head and fatty tissues

Fish heads are commonly used to make soups and broths, but they can contain more than just meat and connective tissue.

Depending on the species and environment, contaminants may be present in tissues around the head and in fatty portions. EPA materials note that some fish-consumption advisories specifically warn against eating heads and other parts because certain contaminants, including PCBs, can concentrate in them.

Fat is also relevant. The FDA advises that, for some locally caught fish, removing skin and fat can reduce exposure to certain pollutants that may accumulate in those tissues.

Again, this is not a universal rule that every fish head is dangerous. The actual risk depends on the fish and where it came from.

What About the Kidneys?

This is where the headline deserves an important clarification.

There is no good evidence that routinely eating a particular part of ordinary store-bought fish directly causes kidney disease.

However, certain environmental contaminants found in fish can affect the kidneys at sufficiently high or prolonged exposure. For example, the World Health Organization states that mercury can have toxic effects on several organs, including the kidneys, while the FDA notes that prolonged cadmium exposure can contribute to kidney dysfunction.

That is why the bigger issue is not simply “which fish part is poisonous?” It is how much contamination the fish contains and how frequently you consume it.

Mercury Is Another Reason to Be Selective

Mercury is one of the best-known contaminants associated with seafood.

Nearly all fish contain at least trace amounts of methylmercury, but levels vary considerably. Larger, longer-lived predatory fish tend to accumulate more because they eat other fish over time.

The FDA currently places several species in its highest-mercury “Choices to Avoid” category, including:

• King mackerel
• Marlin
• Orange roughy
• Shark
• Swordfish
• Gulf of Mexico tilefish
• Bigeye tuna

This doesn't mean you need to stop eating fish. In fact, the FDA emphasizes that fish can be part of a healthy diet and recommends choosing a variety of lower-mercury fish.

The Safer Way to Enjoy Fish

Instead of avoiding seafood altogether, focus on species, source, preparation, and variety.

When buying fish:

Choose lower-mercury species more often. Salmon, sardines, trout, tilapia, cod, pollock, and several other species are included among the FDA's “Best Choices.”

Be more cautious with large predatory fish. Species that live longer and eat other fish can accumulate higher levels of methylmercury.

If eating locally caught fish, check local advisories. Contaminant levels can vary dramatically between waterways, and authorities may issue specific recommendations about which species—or even which parts of a fish—to avoid.

Don't assume cooking removes mercury. The FDA notes that cleaning or cooking does not reduce the amount of methylmercury already present in fish tissue. Choosing a lower-mercury species is the more effective strategy.

The Bottom Line

Fish can absolutely be part of a healthy diet. The concern is mainly about contamination and repeated exposure, not the idea that fish itself is unhealthy.

If you eat whole fish, be especially cautious about internal organs, liver, heads, and fatty tissues, particularly when the fish is wild-caught from waters with known or uncertain contamination. Some pollutants can concentrate in these tissues.

And while the claim that “one fish part may harm your kidneys” is too broad, certain contaminants—including mercury and cadmium—can affect kidney health at sufficiently high or prolonged exposure.

The smartest approach isn't to fear fish—it is to choose the right fish, know where it comes from, and avoid unnecessary exposure to potentially contaminated parts.

Sources

• FDA — Advice About Eating Fish
• FDA — Questions & Answers About Eating Fish and Contaminants
• U.S. EPA — Fish Sample Types and Advisories
• World Health Organization — Mercury and Health
• FDA — Cadmium in Food and Foodwares