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Ciguatera Poisoning

Posted in Our Blog on August 23, 2023

Ciguatera sounds a lot like a cryptid you’d hear about on a podcast. The reality is way more ominous than that. Ciguatera poisoning affects about 500,000 people each year.

Ciguatera poisoning is caused by ingesting the ciguatoxin present in certain fish. Researchers have discovered the source – algae.  Fish eat the algae, and although there are no outward signs of illness in the fish, it can be very poisonous to humans.

Certain large reef fish harvested in warm waters carry an increased risk of ciguatera poisoning. A team of researchers in Canada have collaborated with experts at the University of South Alabama, the University of Texas at Austin, the University of the US Virgin Islands, and the Norwegian Veterinary Institute to learn more about this novel toxin.

Highest Risk Fish

Ciguatera poisoning has been linked to large reef fish primarily in the Caribbean Sea, the Indian Ocean, and the Pacific Ocean. However, additional research has found the toxin in the Canary Islands, the eastern Mediterranean Sea, and the western Gulf of Mexico.

Not all fish hold onto the toxin. The most common carriers include:

  • Amberjack
  • Barracuda
  • Grouper
  • Moray eel
  • Sea bass
  • Snapper
  • Sturgeon

Algae to Blame

The fish, on their own, are not toxic. The problem comes when the fish consume certain algae. Smaller fish eat the algae, filling their bodies with the toxin. Larger fish eat the smaller fish. As the toxins move through the food chain (smaller fish being eaten by bigger fish, and then bigger fish eat those fish, etc.) the toxins become more and more concentrated. This toxin does not harm the fish in any way; however, it is harmful to the humans that eat the fish.

Previous Research Focused on Identifying Source

It was believed that the source of the toxin was algae. Poisoning cases were more prevalent in warm water conditions. A time when algae grow and thrive. Researchers collected and analyzed algal samples and finally found the source of the toxin.

Until this point, researchers were looking to identify toxins produced by algae. But this is a vast category.

“We have an extensive history of successful research on toxins produced by algae but, until recently, have not tackled certain compound classes, including ciguatoxins,” explains Pearse McCarron, a researcher leading the National Research Council of Canada (NRC) Biotoxin Metrology Group.

This effort began around 2018 and was aimed at addressing the “huge global problem” of ciguatoxins. One of the toxins affecting the food supply.

A Joint Effort

Teams in the United States collect algae samples from coral reefs, with the current focus being in the Caribbean. They are established the cultures to grow algae and screened them for toxicity.

The Canadian team is performed chemical profiling and identification to determine the structure of the toxin.

The Norwegian team worked on enzyme incubation experiments to confirm that the algal toxin transforms the toxin that is found in the fish.

New Research Focuses on Food Safety

This year, the research has changed focus. Now that the algae research has identified a specific toxin and source, research is moving toward helping to translate this information onto food safety efforts.

Researchers are considering how fish species metabolize the toxin, allowing it to cause ciguatera poisoning in humans. If successful, this information will be groundbreaking research that will allow a tool for food safety laboratories.

“The findings will make it possible to develop methods and standards to help food safety laboratories monitor and manage ciguatera. And that will go a long way toward dealing with the problem and hopefully preventing the illness in humans.”
–Pearse McCarron, NRC Biotoxin Metrology Group

This research continues as a joint effort between the United States, Canadian, and Norwegian researchers in an effort to help protect consumers and the food supply.

“Our varied approach and multidisciplinary team led to this breakthrough. The findings, published in an article in the journal Chemosphere, will make it possible to develop methods to understand the distribution of these toxins in the food web and ultimately help establish monitoring programs to protect consumers. And this will contribute greatly to food safety.”
– Elizabeth Mudge, NCR specialist in food science and chemistry.

Pearse hopes that research tools and reference materials for food safety scientists will eventually evolve out of this research.

Ciguatera Poisoning Symptoms

Symptoms of Ciguatera Poisoning often develop within 24 hours of eating contaminated fish; however, they may begin as early as minutes after ingestion in some cases.

Initial Gastrointestinal Symptoms

Initial Ciguatera poisoning symptoms are gastrointestinal in nature. Typical symptoms include:

  • Nausea
  • Vomiting
  • Diarrhea
  • Abdominal pain

Gastrointestinal symptoms may last for several days.

Neurological Symptoms

Ciguatera poisoning is more known for the neurological symptoms caused by toxin. Typical symptoms include:

  • Tingling and numbness around the mouth, lips, throat, arms, and legs
  • Sore muscles and tooth pain
  • Temperature reversal (hot things feel cold and cold things feel hot)
  • Tired feeling
  • Headaches
  • Itchy skin

Most people recover completely from ciguatera poisoning within a few days or weeks. In more severe cases, neurological symptoms may persist for months or longer. In very rare cases, ciguatera poisoning can be fatal.


There is no known cure for ciguatera poisoning. Symptoms generally resolve on their own. Certain treatments may provide relief from some of the symptoms, but the infected person is limited to riding the symptoms out until they pass.

How to Prevent Ciguatera Poisoning

Without availability of detection or treatment options, the safest way to prevent ciguatera poisoning is to prevent it.

Contaminated Fish Cannot be Obviously Identified

There is no way to identify if a fish is contaminated. The toxin is tasteless, odorless, and the fish will not appear different in any way.

Cooking Will Not Eliminate Toxin

Cooking or preparing contaminated fish will not remove the toxin. Ciguatera toxin cannot be destroyed by cooking, smoking, freezing, canning, salting, or drying. If the fish is potentially contaminated, there is no way to get rid of it.

Avoid Eating Reef Fish

Your best bet is to avoid eating potentially contaminated fish. Avoid eating the higher risk large reef fish such as: amberjack, barracuda, grouper, moray eel, sea bass, snapper, and sturgeon fish.

If you cannot avoid eating the high-risk fish, only eat smaller fish (less than 3 kg). Just remember that small fish may still contain the toxin. Do not consume the heads, viscera (organs and intestines), and roe (eggs) of reef fish. These areas are suspected to contain higher levels of toxins, but research in that area is not definitive.

If you are traveling or sport fishing, do not consume fish caught in areas that have been associated with ciguatera poisoning cases. Always avoid eating fish that the local population considers dangerous.

By: Heather Van Tassell