The four most serious illnesses related to eating toxic fish are ciguatera, paralytic shellfish poisoning, scombroid poisoning and tetrodotoxin poisoning. Several symptoms of these fish toxicities are presented.

Some species of marine life cause illness when eaten by humans. Illnesses related to eating toxic fish are becoming more common in the United States because of increased fish consumption. You don’t have to eat a toxic fish in the tropics – the toxic fish can be sent to you wherever you are. Of the many types of poisoning, four stand out because of their seriousness. These are ciguatera, paralytic shellfish poisoning (PSP), scombroid poisoning and tetrodotoxin poisoning.

There are many reports of ciguatera poisoning in tropical latitudes. One small epidemic was described on a live-aboard dive boat, where all the divers became sick from eating fish caught on the reefs. A case of scombroid poisoning was described in a Midwest hospital when a Marlin was purchased by the cafeteria and served to many of the employees. Described below are the characteristics of the most common fish toxicities.

CIGUATERA POISONING

This is caused by many fish commonly found in tropical waters. The toxin is a heat-stable compound that originates from dinoflagellates (a species of plankton). The toxin passes through the food chain and is concentrated in fish such as Red Snapper, Amberjack, Barracuda and Surgeonfish. Ingestion of the affected fish, whether cooked or raw, can produce poisoning.

The victim usually notices symptoms within 12 hours. Often, symptoms will appear within minutes. Presentation may vary from minor tingling in the mouth to coma and death. Tingling sensations, abnormal hot/cold sensations and joint and muscle pains are common. Abdominal cramps, diarrhea, nausea and vomiting are less common. The disease is most severe for 6 to 10 days but many victims complain of symptoms for a year or more. Some victims have a recurrence of symptoms when any fish product is ingested.

There are no diagnostic tests for the victim, although there is a test for the toxin in suspected fish. Because the disease is common in certain areas, it is important to seek advice from natives of the area before eating any fish from local waters.

Treatment of ciguatera poisoning is primarily supportive. A variety of treatments have been suggested but none has been highly successful. The clinical features of ciguatera are shown in the sidebar.

PARALYTIC SHELLFISH POISONING

This occurs in humans after ingestion of shellfish contaminated by toxins from plankton known as dinoflagellates. These plankton “bloom” in certain temperatures. They often become concentrated enough to color the water. The red and yellow tides that occur periodically throughout the world are owing to a proliferation of these plankton. The high concentration may deplete the sea of oxygen and cause death of fishes but clams or oysters can filter these organisms and concentrate the toxin in their muscles. Contamination may be found in mussels, beach and surf clams, razor clams and butter clams among others.

The illness may take on different manifestations. One form causes nausea, vomiting, diarrhea and abdominal pain. Symptoms usually appear about 12 hours after eating the shellfish. The paralytic type begins with immediate sensations of tingling in the mouth and lips after eating a contaminated shellfish. The sensation spreads to the rest of the body. Numbness may follow the tingling and ultimately, paralysis develops. Dizziness, increased salivation, thirst, difficulty with talking and breathing may occur. In some subjects the symptoms are typical of an allergic reaction, with wheezing and swelling of the throat.

There is no specific treatment. If mouth tingling is noticed, the food should be immediately removed from the mouth. When food has been swallowed and the victim is sick, vomiting should be induced if medical help is not available. When muscle paralysis is present, careful surveillance of breathing should be done and breathing assistance provided if necessary.

SCOMBROID POISONING

This form of poisoning originates in the scombroid fishes, which include tuna, mackerel, skipjack, bonito and albacore. Epidemics have been related to canned tuna. The disease occurs when the fish, which are usually safe to eat, are left for several hours at room temperature or outside in a warm climate. When at room temperature for several hours, histidine in the muscle tissues is converted to saurine, a drug that causes a spicy or peppery taste. Within 30 to 60 minutes, the subject experiences headache, flushing, dizziness, throbbing of blood vessels, palpitations and rapid heartbeat. Blood pressure may drop. In addition, wheezing, hives and shock may occur. Other symptoms include nausea, vomiting, diarrhea, abdominal pain and thirst. Treatment includes emptying the stomach, support for shock and breathing support. Antihistamine drugs are considered effective.

TETRODOTOXIN POISONING

This is typified by the well-known fugu poisoning in Japan. Fugu poisoning occurs from ingestion of the Asian Pufferfish, which contains lethal amounts of the poison in the gonads and liver. The toxin blocks the normal action of the nerves and the heart cells. The severity depends on the amount of toxin ingested. In Japan, specially trained fugu chefs are considered experts if they leave small amounts of the toxin in the fish to provide a mild tingling sensation in the mouth. Death from a large dose of toxin is common.

Nerve involvement often begins with muscular twitching and may progress to total paralysis. Speech and respiration may be compromised. The victim may be totally immobile but conscious and aware of all that is going on. Treatment for early poisoning includes removing stomach contents and support of breathing. When paralysis occurs, breathing support is needed for 24 hours or more. The toxic effects usually remit spontaneously if the victim is supported. Sedation should be given to the totally paralyzed patient. No specific treatment has proven effective.

The incidence of poisoning from fish is increasing. You should be aware of these illnesses and make an effort to know where the fish you eat come from. Divers in the tropics are especially at risk for ciguatera poisoning. A fresh fish cookout on the beach during a tropical dive trip has resulted in ciguatera poisoning more than once.

SYMPTOMS OF CIGUATERA POISONING

  • Mouth or face tingling
  • Tingling of hands or feet
  • Cold to hot reversal
  • Paralysis
  • Coma
  • Abdominal pain
  • Diarrhea
  • Nausea
  • Vomiting
  • Muscle pain in extremities
  • Joint pains

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