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Fish Poisoning and Shellfish Poisoning


Gerald F. O’Malley

, DO, Grand Strand Regional Medical Center;

Rika O’Malley

, MD, Grand Strand Medical Center

Last full review/revision Apr 2020| Content last modified Apr 2020
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Fish poisoning and shellfish poisoning commonly cause gastrointestinal, neurologic, or histamine-mediated manifestations.

Ciguatera poisoning

Ciguatera poisoning may result from eating any of > 400 species of fish from the tropical reefs of Florida, the West Indies, or the Pacific, where a dinoflagellate produces a toxin that accumulates in the flesh of the fish. Older fish and large fish (eg, grouper, snapper, kingfish) contain more toxin. No known processing procedures, including cooking, are protective, and flavor is unaffected. No commercial product is available to test for ciguatoxin in fish.

Symptoms may begin 2 to 8 hours after eating. Abdominal cramps, nausea, vomiting, and diarrhea last 6 to 17 hours; then, pruritus, paresthesias, headache, myalgia, reversal of hot and cold sensation, and face pain may occur. For months afterward, unusual sensory phenomena and nervousness may cause debilitation.

IV mannitol has been suggested as a treatment, but no clear benefit has been shown.

Scombroid poisoning

Scombroid poisoning is caused by high histamine levels in fish flesh due to bacterial decomposition after the fish is caught. Commonly affected species include

  • Tuna

  • Mackerel

  • Bonito

  • Skipjack

  • Mahi mahi

The fish may taste peppery or bitter. Facial flushing and possibly nausea, vomiting, epigastric pain, and urticaria occur within a few minutes of eating and resolve within 24 hours. Symptoms are often mistaken for those of a seafood allergy. Unlike other fish poisonings, this poisoning can be prevented by properly storing the fish after it is caught.

Treatment may include H1 and H2 blockers.

Tetrodotoxin poisoning

Tetrodotoxin poisoning is most commonly due to eating the puffer fish (fugu), a Japanese delicacy, but > 100 freshwater and saltwater species contain tetrodotoxin. Early symptoms include paresthesias in the face and extremities, followed by increased salivation, nausea, vomiting, diarrhea, and abdominal pain. Potentially fatal respiratory paralysis can also occur. Treatment is supportive care with attention to ventilatory assistance until the toxin is metabolized, which may take days.

The toxin cannot be destroyed by cooking or freezing.

Shellfish poisoning

Paralytic shellfish poisoning can occur from June to October, especially on the Pacific and New England coasts, when mussels, clams, oysters, and scallops are contaminated by the poisonous dinoflagellate responsible for red tide. This dinoflagellate produces the neurotoxin saxitoxin, which is resistant to cooking. Circumoral paresthesias occur 5 to 30 minutes after eating. Nausea, vomiting, and abdominal cramps then develop, followed by muscle weakness. Untreated respiratory paralysis may be fatal; for survivors, recovery is usually complete.

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More than 60,000 bites and stings are reported to poison centers in the US each year, about 45,000 of which are snakebites (of which 7,000 to 8,000 are venomous and cause about 5 deaths). Which of the following types of snakes accounts for the majority of these bites and almost all deaths? 
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