Ciguatera fish poisoning (CFP), also known as ciguatera, is a foodborne illness caused by eating tropical reef fish contaminated with ciguatoxins. Such individual fish are said to be ciguatoxic. Symptoms may include diarrhea, vomiting, numbness, itchiness, dysesthesia, sensitivity to hot and cold, dizziness, and weakness with lethargy. The onset of symptoms varies with the amount of toxin absorbed. If a large quantity of toxins is consumed, symptoms may appear within half an hour. At lower amounts, symptoms may take a few days to appear. Diarrhea may last up to four days. Symptoms may last a few weeks to a few months. Heart problems such as slow heart rate and low blood pressure may occur.

The specific toxins involved are the ciguatoxins and maitotoxin. They are made by a small marine organism, Gambierdiscus toxicus, that grows on and around coral reefs in tropical and subtropical waters. These are eaten by herbivorous fish which in turn are eaten by larger carnivorous fish. The toxins become more concentrated as they move up the food chain. The fish most often implicated include barracuda, grouper, moray eel, amberjack, sea bass, and sturgeon. Diagnosis is based on a person's symptoms together with having recently eaten fish. If a number of those who eat the same fish develop symptoms the diagnosis becomes more likely. If some of the fish they had previously eaten is available this can also be tested to confirm the diagnosis.

Preventive efforts include not eating reef fish, not eating high-risk fish such as barracuda, and not eating fish liver, roe, or fish heads. Ciguatoxin has no taste or smell, and cannot be destroyed by conventional cooking. There is no specific treatment for ciguatera fish poisoning once it occurs. Mannitol may be considered, but the evidence supporting its use is not very strong. Gabapentin or amitriptyline may be used to treat some of the symptoms.

In 2017, the United States Centers for Disease Control (CDC) estimated that around 50,000 cases occur globally each year. Other estimates suggest up to 500,000 cases per year. The risk of death from poisoning is less than 1 in 1,000 according to the CDC. It is the most frequent seafood poisoning. It occurs most commonly in the Pacific Ocean, Indian Ocean, and the Caribbean Sea between the latitudes of 35°N and 35°S. The risk of the condition appears to be increasing due to coral reef deterioration and increasing trade in seafood. Descriptions of the condition date back to at least 1511. The current name, introduced in 1787, is of Cuban Spanish origin and originally referred to the gastropod Cittarium pica.

Hallmark symptoms of ciguatera in humans include gastrointestinal, cardiovascular, and neurological effects. Gastrointestinal symptoms include nausea, vomiting, and diarrhea, usually followed by neurological symptoms such as headaches, muscle aches, paresthesia, numbness of extremities, mouth and lips, reversal of hot and cold sensation, ataxia, vertigo, and hallucinations. Severe cases of ciguatera can also result in cold allodynia, which is a burning sensation on contact with cold. Neurological symptoms can persist and ciguatera poisoning is occasionally misdiagnosed as multiple sclerosis. Cardiovascular symptoms include bradycardia, tachycardia, hypotension, hypertension, orthostatic tachycardia, exercise intolerance, and abnormal electrocardiograms. Death from the condition can occur, but is very rare.

Dyspareunia and other ciguatera symptoms have developed in otherwise healthy males and females following sexual intercourse with partners suffering ciguatera poisoning, signifying that the toxin may be sexually transmitted. Diarrhea and facial rashes have been reported in breastfed infants of poisoned mothers, suggesting that the polyether toxins partition into breast milk.

The symptoms can last from weeks to years, and in extreme cases as long as 20 years, often leading to long-term disability. Most people do recover slowly over time.

Gambierdiscus toxicus is the primary dinoflagellate responsible for the production of a number of similar polyether toxins, including ciguatoxin, maitotoxin and possibly palytoxin. Other dinoflagellates that may cause ciguatera include other Gambierdiscus and Fukuyoa spp.