When Fish Make You Sick

To eat or not to eat-this was Arebonto’s dilemma. He knew the risk, but he was hungry. And the barbecued fish smelled delicious. His appetite won out. But the rapid onset of nausea and abdominal pain followed by vomiting and diarrhea made him wish he had not eaten the fish.
By the time friends rushed Arebonto to the hospital on his small Pacific island, he was semiconscious and dehydrated and had chest pains, dangerously low blood pressure, and a slow pulse. Over the next few days, in addition to headaches, dizziness, and fatigue, he experienced numbness in his legs, painful urination, and a strange sensory reversal whereby cold felt hot and hot felt cold. After eight days his pulse rate stabilized, but numbness and fatigue persisted for weeks.
Arebonto had fallen victim to potent, naturally occurring toxins that contaminate otherwise normally edible tropical reef fish. The condition, known as ciguatera fish poisoning (CFP), occurs in tropical and subtropical regions of the Indian and Pacific oceans and in the Caribbean. In these areas, locally caught fish are a major food source.
CFP is not a new disease. In fact, it was the bane of European maritime explorers. Likewise, many a present-day vacationer has suffered from its debilitating effects. Understandably, the disease imposes constraints on the fishing and tourist industries of many island nations. Moreover, international trade in live and frozen reef fish has extended the geographic range of CFP beyond the Tropics to places where it is not readily recognized.
What causes reef fish to become toxic? Can toxic fish be identified? Consider what decades of research has revealed.
Identifying the Culprit
A microorganism called a dinoflagellate is generally regarded as the source of the toxins that cause CFP. The microbe lives on dead coral and attaches itself to algas. Small fish graze on the algas and ingest the toxins-called ciguatoxins-produced by the dinoflagellates. These fish are eaten by larger fish, which, in turn, are eaten by still others, concentrating the toxins higher up the food chain. The fish, however, seem unaffected.
Ciguatoxins are among the most lethal biological substances known. Fortunately, “only a few species of fish are incriminated in CFP,” says an Australian government paper. Ciguatoxins do not alter the appearance, smell, or taste of fish and cannot be destroyed by cooking, drying, salting, smoking, or marinating. In Arebonto’s case, nothing about the fish he ate warned him of the hidden menace until he experienced severe gastrointestinal, cardiovascular, and neurological symptoms.
Diagnosis and Treatment
At present there is no laboratory test for CFP in humans. Diagnosis is based on the appearance of a variety of symptoms, which usually appear within hours after eating and may be confirmed by testing leftover fish for toxins. If you suspect CFP, it is wise to seek medical help. Although there is no known antidote, treatment may relieve the symptoms, which usually subside within a few days. However, CFP can be debilitating, and early treatment may prevent its affects from becoming chronic.
The severity of the symptoms varies, depending on a number of factors. These include the toxicity of the fish, the amount and the parts of the fish eaten, the level of the ciguatoxins already in the patient, and the geographic origin of the fish, for toxins seem to differ slightly from region to region. Instead of developing an immunity to these toxins, humans become more sensitive, making repeat attacks even worse! Consuming alcohol also exacerbates symptoms. To avoid a relapse, the patient should refrain from eating fish for three to six months after a bout with CFP, explains a publication on this widespread disease.
Severe cases may last for weeks or months and sometimes even for years, resulting in symptoms similar to chronic fatigue syndrome. In rare cases, death occurs from shock, respiratory or heart failure, or dehydration. Such cases, though, are usually associated with the consumption of tissue where toxins are more concentrated, such as the head or the internal organs of the fish.
An Enduring Enigma
Virtually all fish that inhabit coral reefs, and their predators, are potentially ciguatoxic. But herein lies an enigma. Fish from one reef area may be highly toxic, but the same species caught nearby may be safe. A frequently implicated species in one part of the world may be considered safe in another. Since the release of toxins by dinoflagellates is erratic, the occurrence of toxic fish is unpredictable.
Adding to the problem, a cost-effective, reliable test for toxic fish remains elusive. The best that health authorities can do at present is to inform the public of what fish to avoid and where these might be caught-information that is based on reported cases of CFP. Highly suspect species include barracuda, grouper, kingfish, red bass, rockfish, and snapper, as well as moray eel. Older, larger fish usually present a higher risk. In some places it is illegal to sell potentially unsafe fish. However, pelagic fish that do not prey on reef fish and fish from temperate waters are generally considered to be safe.
The incidence of CFP is predicted to rise. In part, this is because dead coral creates an environment favorable to the proliferation of toxic dinoflagellates, and reports indicate that a growing number of coral reefs are either sick or dying.
Despite the unpredictable nature of CFP, you can minimize the risk by observing some basic principles. Arebonto almost died because he did not follow these guidelines. He ate the head and flesh of a local rockfish known to pose a high risk. He had eaten that species before without ill effects and, like many other islanders, became overconfident.
Does the foregoing mean that you should avoid seafood, perhaps while enjoying a tropical vacation? Not at all. The prudent course is to observe the warnings and to choose your fish wisely.



Common Symptoms
▪ Diarrhea, nausea, vomiting, abdominal cramps
▪ Chills, sweating, dizziness, headaches, itching
▪ Numbness or tingling around the mouth, hands, or feet
▪ Sensory reversal-cold feels hot, hot feels cold
▪ Pain in muscles and joints and when urinating
▪ Slow pulse rate, low blood pressure, fatigue

Minimize the Risk
▪ Ask the local fisheries department or fishing experts about the fish to avoid and the areas where toxic fish are caught.
▪ Avoid eating fish from areas where ciguatera was recently reported.
▪ Avoid eating older, larger reef fish.
▪ Do not eat the head or the liver or other internal organs.
▪ As soon as you catch a reef fish, gut it properly.


As a result of misdiagnoses and underreporting, the true worldwide incidence of CFP is not known. Various authorities estimate that some 50,000 cases occur worldwide annually.