Fish poisoning - including symptoms, treatment and prevention

There are four main types of poisoning that can result from eating fish. See below the relevant type of poisoning for information including signs, symptoms, diagnosis and treatment.

Food poisoning is a notifiable condition1

Ciguatera fish poisoning

Ciguatera poisoning is a form of food poisoning caused by eating warm water ocean fish that have ciguatera poison (toxin). The toxin is produced by a small organism called a dinoflagellate, which attaches to algae in warm ocean water reef areas. Small plant eating fish eat this algae, and the toxin then accumulates and is concentrated in larger predatory fish. Many species of fish have been known to cause ciguatera poisoning in humans.

The toxin does not affect the appearance, odour or taste of the fish and is not destroyed by cooking, refrigeration or freezing.

Signs and symptoms

Symptoms usually occur within 1 to 24 hours of eating a toxic fish and include:

  • vomiting
  • diarrhoea and/or abdominal (stomach) cramps
  • headaches, fatigue and fainting
  • joint and muscle pain
  • tingling around the mouth, fingers and toes
  • burning sensation or skin pain on contact with cold water
  • extreme itchiness
  • coma in severe cases.

Seek medical attention at the onset of symptoms.

Diagnosis

Diagnosis is confirmed by the detection of ciguatoxin in fish linked to the case of poisoning.

People recovering from ciguatera fish poisoning should avoid eating warm water ocean fish for at least 6 months, and avoid alcohol for at least 3 months.

Prevention

Avoid eating large warm water fish, especially the head, roe, liver and other internal organs where ciguatera toxin is more concentrated.

Scombroid fish poisoning (Histamine Poisoning)

Histamine poisoning can be caused by eating spoiled fish of the:

  • Scombridae family - includes tuna, mackerel and bonito
  • non-scombroid fish - includes bluefish, sardines, marlin and mahi mahi.

If fish are caught in warm areas and are not refrigerated properly, a chemical called histidine, that exists naturally in man fish, can break down to histamine which causes symptoms within a few hours of eating the fish.

Signs and symptoms

Symptoms include:

  • tingling and burning around the mouth
  • facial flushing and sweating
  • nausea, vomiting and diarrhoea
  • headache
  • palpitations and dizziness
  • rash.

These symptoms usually resolve within 12 hours with no long term effects.

Diagnosis and treatment

Diagnosis is confirmed by detection of histamine in fish linked to the case of poisoning. In severe cases, treatment with antihistamines may be effective.

Prevention

Fish should be chilled and properly refrigerated as soon as possible after being caught to prevent histamine formation.

Shellfish poisoning (paralytic, neurotoxic and amnesic shellfish poisoning)

Some organisms present in seawater and ingested by shellfish may produce a toxin. These organisms are particularly numerous during algal blooms or ‘red tides’. Symptoms occur within minutes to hours after eating the shellfish.

Signs And Symptoms

Paralytic shellfish poisoning can be very serious and can sometimes cause death.

Symptoms may begin with tingling around the mouth, face, fingers and toes.

Paralytic symptoms usually settle within a few days, but in severe cases, affected people may stagger and may not be able to talk, swallow, move or breathe.

Neurotoxic shellfish poisoning has similar symptoms to ciguatera poisoning, but is usually less severe and lasts only a few days.

Amnesic shellfish poisoning can be serious, causing vomiting, abdominal cramps and diarrhoea, usually within a day of eating the affected shellfish. Confusion, amnesia (loss of memory) and coma may follow in severe cases. The amnesia may be permanent.

Prevention

Fish caught during algal blooms or during warnings not to fish should not be eaten.

Diagnosis

Diagnosis is confirmed by detection of toxins in implicated shellfish.

Incubation period

(time between exposure and developing symptoms)

Symptoms may occur within minutes to 2 hours after consuming the affected shellfish

Rudderfish / escolar diarrhoea

This is caused by eating fish belonging to the escolar and oilfish groups. These fish have a high wax ester (oil) content. In humans, these wax esters cannot be digested and may accumulate in the bowel causing oily diarrhoea.

Signs and symptoms

Symptoms normally include the sudden onset of watery and oily diarrhoea with abdominal cramps. Nausea, headache and vomiting have also been reported.

Diagnosis

Diagnosis is made by testing the implicated fish for oil types, concentration, and by identification of the type of fish.

Incubation period

(time between exposure and developing symptoms)

The average is about 2 to 2½ hours, but can range from 1 to 90 hours. The illness lasts for an average of 22 to 24 hours, with a range from 5 to 78 hours.

Prevention

Seafood retailers are encouraged to display signs advising that escolar and oilfish might cause symptoms.

Useful links

1 – In South Australia the law requires doctors and laboratories to report some infections or diseases to SA Health. These infections or diseases are commonly referred to as 'notifiable conditions'.