Categories of Seafood Poisons

Food Toxicology 2(2+0)
Lesson 12 : Animal Toxins and Plant Toxicants

Categories of Seafood Poisons


Food source

Mode of action



Fish - tuna, and mackerel-like fish. Other products have also caused toxic effects, such as cheeses, the primary being Swiss cheese.
Cooking, canning, or freezing do not reduce the toxic effect.

The toxic symptoms are due to histamine formed.

After ingestion or within 2 h, the patient shows several gastrointestinal effects, such as nausea, vomiting, and diarrhea, as well as epigastric distress, headache, and burning sensation of the throat. This can be followed by neurological numbness, tingling, cutaneous flushing, and urticaria. Symptoms subside in ca. 16 h and generally there are no lasting ill effects. The duration of the illness is usually 3 h, but may last several days.


Species of clams, mussels, and other shellfish that feed on the algae produce a toxin

The active toxin is known as saxitoxin and the LD 50
of an injection (IP) of saxitoxinin mice is 10 mg/kg.

Saxitoxin, has a direct effect on the heart and blocks action potentials in nerves and muscles. Symptoms of the disease develop fairly rapidly, 30 min to 2 h after ingesting the shellfish, depending on the amount of the toxin consumed. In severe cases, respiratory paralysis is common, and death may occur if respiratory support is not provided.


Puffer fish, which include blowfish, porcupine fish, toadfish, fugu (sold in Japanese restaurants ). The toxin is stable to boiling temperatures,
unless made alkaline. Certain bacteria can produce the toxin and may be the source of the poison.

Tetrodotoxin, a neurotoxin, results in paralysis of the CNS and peripheral nerves. The oral LD
50 in mice is 322

It provokes hypotension and aversely affects respiration. The initial tingling sensations can be followed by malaise; dizziness; pallor; numbness of the extremities, lips, and tongue; and subsequent nausea, vomiting, ataxia, and diarrhea. Other symptoms include subcutaneous hemorrhage, desquamation, respiratory distress, muscular twitching, tremors, in coordination, muscle paralysis, cyanosis, and convulsions, and ca. 40 to 60% deaths can occur. Symptoms appear usually in 10 to 45 min; however, a lag time of 3 h or more has also been observed.


Ciguatoxin, is produced by more than 300 species of fish especially snail. Many fish caught for food have ciguatoxin as the food they eat contain
the toxin.

Ciguatoxin results in disruption of nerve function. Death is usually attributed to respiratory paralysis.

Ciguatoxin poisoning begins with tingling of lips, tongue, and throat, and is rapidly followed by numbness in those areas. It may take up to 30 h following ingestion of the fish for symptoms to appear. Nausea, vomiting, abdominal pain with intestinal spasms, and diarrhea soon follow. Patients complain of headaches, which can be followed by muscle pain, visual disturbances, dermatitis, and even convulsions. Usually,
poisoning is treated symptomatically. About 7% of the cases result in fatalities.

Last modified: Thursday, 23 February 2012, 7:38 AM