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Poisoning - fish and shellfish


This article describes a group of different conditions caused by eating contaminated fish and seafood. The most common of these are Ciguatera poisoning, Scombroid poisoning, and various shellfish poisonings.

This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an exposure, you should call your local emergency number (such as 911) or 1-800-222-1222 for a local poison control center.

Alternative Names:

Fish poisoning; Dinoflagellate poisoning; Seafood contamination; Paralytic shellfish poisoning; Ciguatera poisoning

Poisonous Ingredient:

In Ciguatera poisoning, the poisonous ingredient is ciguatoxin. This is a poison made in small amounts by certain algae and algae-like organisms called dinoflagellates. Small fish that eat the algae become contaminated. If larger fish eat a lot of the smaller, contaminated fish, the poison can build up to a dangerous level, which can make you sick if you eat the fish. Ciguatoxin is "heat-stable." That means it does not matter how well you cook your fish, if the fish is contaminated, you will become poisoned.

In Scombroid poisoning, the poisonous ingredient is a combination of histamine and similar substances. After the fish dies, bacteria create large amounts of the toxin if the fish is not immediately refrigerated or frozen.

In shellfish poisoning, the poisonous ingredients are toxins made by algae-like organisms called dinoflagellates, which build up in some types of seafood. There are many different types of shellfish poisoning. The most well-known types are paralytic shellfish poisoning, neurotoxic shellfish poisoning, and amnesic shellfish poisoning.

Where Found:

Ciguatera poisoning normally occurs in larger fish from warm tropical waters. The most popular types of these fish used for food include sea bass, grouper, and red snapper. In the United States, the waters around Florida and Hawaii are most likely to have contaminated fish.

The risk is greatest in the summer months, or any time a large number of algae are blooming in the ocean, such as during "red tide." A red tide occurs when there is a rapid increase in the amount of dinoflagellates in the water. However, thanks to modern transportation, anyone around the world may eat a fish from contaminated waters.

Scombroid poisoning usually occurs from large, dark meat fish such as tuna, mackerel, mahi mahi, and albacore. Because this poison develops after a fish is caught and dies, it does not matter where the fish is caught. The main factor is how long the fish sits out before being refrigerated or frozen.

Like Ciguatera poisoning, most shellfish poisonings occur in warmer waters. However, poisonings have occurred as far north as Alaska and are common in New England. Most shellfish poisonings occur during the summer months. You may have heard the saying "Never eat seafood in months that do not have the letter R." This includes May through August. Shellfish poisoning occurs in seafood with two shells, such as clams, oysters, mussels, and sometimes scallops.


The harmful substances that cause Ciguatera, Scombroid, and shellfish poisonings are heat stable, so no amount of cooking will prevent you from becoming poisoned if you eat contaminated fish. Symptoms depend on the specific type of poisoning.

Ciguatera poisoning symptoms can occur 2 to 12 hours after eating the fish. They include:

Shortly after these symptoms develop, you will start to have strange sensations, which may include:

  • A feeling that your teeth are loose and about to fall out
  • Confusing hot and cold temperatures (for instance, you will feel like an ice cube is burning you, while a match is freezing your skin)
  • Headache (probably the most common symptom)
  • Low heart rate and low blood pressure (in very severe cases)
  • Metallic taste in the mouth

These symptoms may get worse if you drink alcohol with your meal.

Scombroid poisoning symptoms usually occur immediately after eating the fish. They may include:

  • Breathing problems, including wheezing and chest tightness (in severe cases)
  • Extremely red skin on the face and body
  • Flushing
  • Hives and itching
  • Nausea
  • Peppery or bitter taste
  • Vomiting

Below are other well-known types of seafood poisoning, and their symptoms.

Paralytic shellfish poisoning: About 30 minutes after eating contaminated seafood, you may have numbness or tingling in your mouth. This sensation may spread down to your arms and legs. You may become very dizzy, have a headache, and, in some cases, your arms and legs may become temporarily paralyzed. Some people may also have nausea, vomiting, and diarrhea, although these symptoms are much less common.

Neurotoxic shellfish poisoning: The symptoms are very similar to those of Ciguatera poisoning. After eating contaminated clams or mussels, you will most likely experience nausea, vomiting, and diarrhea. These symptoms will be followed soon after by strange sensations that may include numbness or tingling in your mouth, headache, dizziness, and hot and cold temperature reversal.

Amnesic shellfish poisoning: This is a strange and rare form of poisoning that begins with nausea, vomiting, and diarrhea. These symptoms are followed by short-term memory loss, and other less common nervous system symptoms.

Home Care:

Shellfish poisoning may be a medical emergency. A person with sudden or significant symptoms should immediately be taken to an emergency medical center. You may need to call the local emergency number (such as 911) or poison control for appropriate treatment information.

Before Calling Emergency:

The following information is helpful for emergency assistance:

  • Person's age, weight, and condition
  • Type of fish eaten
  • Time it was eaten
  • Amount swallowed

However, DO NOT delay calling for help if this information is not immediately available.

Poison Control:

In the United States, call 1-800-222-1222 to speak with a local poison control center. This hotline number will let you talk to experts in poisoning. They will give you further instructions.

This is a free and confidential service. All local poison control centers in the United States use this national number. You should call if you have any questions about poisoning or poison prevention. You can call 24 hours a day, 7 days a week.

What to Expect at the Emergency Room:

If you have Ciguatera poisoning, you may receive:

  • Blood and urine tests
  • EKG (electrocardiogram, or heart tracing)
  • Fluids by IV (through a vein)
  • Medicines to stop vomiting
  • Medicines to help reduce nervous system symptoms (mannitol)

If you have Scombroid poisoning, you may receive:

  • Airway support, including oxygen, breathing tube through the mouth (intubation), and breathing machine (ventilator)
  • Blood and urine tests
  • EKG (electrocardiogram, or heart tracing)
  • Fluids by IV (through a vein)
  • Medicines to stop vomiting
  • Medicines to treat severe allergic reactions (if needed), including Benadryl

If you have shellfish poisoning, you may receive:

  • Blood and urine tests
  • EKG (electrocardiogram, or heart tracing)
  • Fluids by IV (through a vein)
  • Medicines to stop vomiting

If shellfish poisoning causes paralysis , you may have to stay in the hospital until your symptoms improve.

Outlook (Prognosis):

Fish and shellfish poisonings occur on occasion in the United States. You can protect yourself by avoiding fish and seafood caught in and around the areas of a known red tide, and by avoiding clams, mussels, and oysters during the summer months. If you are poisoned, your long-term outcome is usually quite good.

Scombroid poisoning symptoms usually only last for a few hours after medical treatment has begun. Ciguatera poisoning and shellfish poisoning symptoms may last from days to weeks, depending on the severity of the poisoning. Only very rarely have serious outcomes or death occurred.

There is no way for the person who prepares the food to know that their food is contaminated. Therefore, it is very important that your doctor tell the restaurant their food is contaminated so that they can throw it away before other people become sick. Your doctor should also contact the Department of Health to make sure that the suppliers providing the contaminated fish are identified, and that all possibly contaminated fish from the same lot are destroyed.


Craig SA. Gastroenteritis. In: Marx JA, Hockberger RS, Walls RM, et al, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 8th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 94.

Goldfrank LR, ed. Goldfrank's Toxicologic Emergencies. 9th ed. New York, NY: McGraw-Hill; 2011.

Review Date: 1/25/2015
Reviewed By: Jacob L. Heller, MD, MHA, Emergency Medicine, Virginia Mason Medical Center, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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