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Toxins in seafood

 

What toxins can be associated with seafood?

  • Amnesic shellfish toxin
  • Diarrhoetic shellfish toxin
  • Neurotoxic shellfish toxin
  • Paralytic shellfish toxin
  • Ciguatoxins
  • Histamine

What illness does it cause?

  • Amnesic shellfish poisoning, diarrhoetic shellfish poisoning, neurotoxic shellfish poisoning and paralytic shellfish poisoning are caused by the respective shellfish toxins listed above
  • Ciguatera (or ciguatera fish poisoning) is caused by ciguatoxins
  • Scombroid fish poisoning is caused by histamine

None of these illnesses are nationally notifiable and don’t need to be reported to health authorities unless there is an outbreak.

What are the symptoms?

Amnesic shellfish poisoning

Symptoms include nausea, vomiting, abdominal cramps, diarrhoea, headaches, confusion and seizures and usually begin within one or two days of eating toxic shellfish.

The illness can be severe and cause coma and death

Diarrhoetic shellfish poisoning

Symptoms include nausea, vomiting, abdominal cramps, diarrhoea and headache and start within 30 minutes to 15 hours of eating toxic shellfish.

The illness usually lasts up to three days.

Neurotoxic shellfish poisoning

Symptoms include numbness and tingling of lips, fingers and toes, nausea, vomiting and diarrhoea.

The illness usually only lasts a few days.

Paralytic shellfish poisoning

Symptoms are similar to neurotoxic shellfish poisoning (see above) but more severe and begin half an hour to two hours after eating toxic shellfish.

The illness can be serious and cause paralysis, respiratory problems and death.

Ciguatera fish poisoning

Symptoms include tingling and numbness in fingers, toes and face; burning sensation or pain on contact with cold water; joint and muscle pains and weakness; nausea, vomiting, diarrhoea, headache, fatigue and fainting. In severe cases, respiratory problems and paralysis can occur. Symptoms start between 1 and 48 hours after eating toxic fish.

Gastrointestinal symptoms usually last a few days but neurological symptoms may last several weeks or months

Scombroid fish poisoning

Symptoms include a peppery or metallic taste, flushing of the upper body, itching, headache, dizziness, vomiting, diarrhoea and abdominal cramps and start 30 minutes to a few hours after eating toxic fish and last a day or two. In severe cases, people can have difficulty breathing and low blood pressure.

Who can get sick?

Anyone who eats contaminated fish or shellfish.

Where do these toxins come from?

The four shellfish toxins listed are produced by certain marine algae. These toxins can build up in shellfish as they feed on the algae, especially during algal blooms (or ‘red tides’). Common shellfish that can be contaminated with these toxins include clams, oysters, mussels, scallops and crabs.

Ciguatoxins come from marine algae that are eaten by fish in and around coral reefs. These toxins build up and become more potent in the bigger fish that feed on contaminated smaller ones. Fish that can contain ciguatoxins include Chinaman fish, red bass, some wrasse, tropical snappers and coral trout.

Histamine is produced by bacteria in particular types of fish (usually in the Scombridae and Scomberesocidae families). When these fish are not properly chilled (straight after capture or in storage before eating) the bacteria can grow and produce high amounts of histamine. Fish that can contain histamine include mackerel, tuna, sardines, anchovy and marlin.

How can people get sick?

  • By eating contaminated fish and shellfish
  • By eating fish that have not been properly chilled
  • Cooking or freezing seafood will not remove the toxins

How can illness be prevented?

  • Buy seafood from a trusted supplier
  • Keep seafood cold (5°C or colder) — refrigerate immediately after buying it; if its frozen, thaw it in the fridge; and if you catch your own fish, chill it on ice immediately
  • Avoid eating large fish from warm ocean waters, especially the head, roe or organs
  • If harvesting shellfish or reef fish yourself, check with local authorities which species and waters are safe for harvesting
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