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Marine Toxins

Topic Overview

What are marine toxins?

Marine toxins are chemicals and bacteria that can contaminate certain types of seafood. Eating the seafood may result in foodborne illness. The seafood may look, smell, and taste normal. There are several types of marine toxins, and they all cause different symptoms.

Foodborne illness through marine toxins is rare. Marine toxin poisoning occurs most often in the summer.

How is marine toxin poisoning diagnosed and treated?

Your doctor will do a medical history and a physical examination and ask you questions about your symptoms and any fish you have recently eaten. Laboratory testing is typically not needed.

There are no specific treatments for marine toxin poisoning. Treatment generally consists of managing complications and being supportive until the illness passes. Dehydration caused by diarrhea and vomiting is the most common complication.

To prevent dehydration, take frequent sips of a rehydration drink (such as Pedialyte). Try to drink a cup of water or rehydration drink for each large, loose stool you have. Soda and fruit juices have too much sugar and not enough of the important electrolytes that are lost during diarrhea, and they should not be used to rehydrate.

Try to stay with your normal diet as much as possible. Eating your usual diet will help you to get enough nutrition. Doctors believe that eating a normal diet will also help you feel better faster. But try to avoid foods that are high in fat and sugar. Also avoid spicy foods, alcohol, and coffee for 2 days after all symptoms have disappeared.

How can I prevent marine toxin poisoning?

Always keep seafood refrigerated or on ice. If you have a weak immune system, you should consider not eating raw seafood.

To help avoid marine toxins:

  • Do not eat barracuda, especially if it is from the Caribbean Sea.
  • Refrigerate fresh tuna, mackerel, grouper and mahimahi. Remember that cooking does not destroy the toxins in spoiled or toxic seafood.
  • Check with health officials about local advisories on algae blooms, dinoflagellate growth, or red tide.
  • Do not eat fish or shellfish sold as bait. These products do not have to meet the same standards as seafood for eating.

What are the types of marine toxin poisoning?

Scombrotoxic fish poisoning:

  • Is caused by bacteria. The bacteria may produce a chemical (histamine) that results in the foodborne illness.
  • Is usually found in fin fish such as tuna, mackerel, and bonito.
  • Causes symptoms within 2 minutes to 2 hours of eating the fish. The most common symptoms are rash, diarrhea, flushing, sweating, headache, and vomiting. Burning or swelling of the mouth, stomach pain, and a metallic taste may also occur. Most people have mild symptoms that are gone within a few hours. In severe cases, antihistamines or epinephrine may be needed.
  • Cooking does not destroy the chemical, so buy your fish from a good source.

Ciguatera poisoning:

  • Is caused by ciguatoxins, which are produced by tiny sea plants called dinoflagellates.
  • Is usually found in tropical reef fish (such as barracuda) that kill other fish. But it may be found in grouper, sea bass, snapper, mullet, and other fish living in tropical waters. Common locations for these fish are the reefs surrounding Hawaii, the Virgin Islands, Puerto Rico, and Guam and other South Pacific Islands.
  • Causes symptoms within a few minutes to 30 hours. Symptoms include nausea, vomiting, diarrhea, cramps, excessive sweating, headache, and muscle aches. A feeling of burning and "pins and needles" as well as weakness, itching, and dizziness can occur. You may also experience unusual taste sensations, nightmares, and hallucinations. Symptoms usually are over in 1 to 4 weeks.
  • Cooking does not destroy the toxins, so buy your fish from a good source.

Paralytic shellfish poisoning:

  • Is caused by a dinoflagellate, although not the same one that causes ciguatera poisoning. These dinoflagellates have a red-brown colour and in large numbers can cause a red streak called "red tide" in the ocean.
  • Is usually found in shellfish in colder coastal waters, such as the Pacific Northwest and New England. Shellfish that have caused the condition include mussels, cockles, clams, scallops, oysters, crabs, and lobsters.
  • Usually causes symptoms within 2 hours of eating the shellfish, although symptoms may occur within 15 minutes or after as long as 10 hours. Symptoms usually begin with numbness or tingling in the face, arms, and legs, followed by headache, dizziness, nausea, and loss of coordination. Symptoms are usually mild, although severe symptoms have occurred.
  • Cooking does not destroy the toxins, so buy your fish from a good source.

Neurotoxic shellfish poisoning:

  • Is caused by a type of dinoflagellate.
  • Is usually found in oysters, clams, and mussels from the Gulf of Mexico and the Atlantic Coast of the southern United States.
  • Cause symptoms in 1 to 3 hours. They include numbness, loss of coordination, an upset stomach, and tingling in the mouth, arms, and legs. They usually last 2 to 3 days.
  • Cooking does not destroy the toxins, so buy your fish from a good source.

Amnesic shellfish poisoning:

  • Is caused by toxins produced by a salt-water plant.
  • Is found in shellfish such as mussels.
  • Causes symptoms within 24 hours. Symptoms include an upset stomach, dizziness, headache, disorientation, and short-term memory loss. Seizures may occur in severe cases.
  • Cooking does not destroy the toxins, so buy your fish from a good source.

Diarrhetic shellfish poisoning (DSP):

  • Is caused by toxins produced by certain microscopic plants.
  • Is found in shellfish.
  • Causes symptoms within 30 minutes to 6 hours. Symptoms include diarrhea, nausea, vomiting, headache, abdominal cramps, and chills. In healthy people, these symptoms usually go away in a few days.
  • Cooking does not destroy the toxins, so buy your shellfish from a good source.


Current as of: July 1, 2021

Author: Healthwise Staff
Medical Review:
E. Gregory Thompson MD - Internal Medicine
Anne C. Poinier MD - Internal Medicine
Adam Husney MD - Family Medicine
W. David Colby IV MSc, MD, FRCPC - Infectious Disease