A large number of marine fish are inherently poisonous. Ciguatera poisoning and tetradon (puffer-fish) poisoning are common examples. Ingestion of fish causes two types of poisoning. The first is due to bacterial growth in partially decomposed fish. The other is a primary toxicity caused by eating some types of sea fishes such as toad fish, cat fish, lion fish, dragon fish due to the presence of a neurotoxin. 99% of cases of fish poisoning are icthyosarcotoxic (involving toxins from muscles, viscera, skin, gonads and mucous surfaces) characterised by various gastrointestinal and neurological disturbances. Rarely, toxicity involves the fish blood or skeleton.
Some fish such as cat fish, muraena (eel), dragon fish, lion fish, stingrays, mantas, scorpion fish, stone fish, cat fish, dog fish, sharks, etc. have extremely sharp dorsal spines equipped with large poisonous sacs. Several families of bony fish have venom glands enveloping sharp spines, which may be dorsal, ventral, behind the head or on the tail. They inject venom through their spines. Poisonous fish usually look no different from fish that are good to eat. Cooking does not destroy the poison. The lesions consist of a row of intensely painful rounded punctures with swelling and redness, which may bleed freely. The rare systemic symptoms, such as abdominal pain with cramps, nausea, vomiting, fits, low blood pressure, respiratory difficulty, circulatory collapse and paralysis are variable. The wound should be cleaned and broken spine removed. The box jellyfish has been described as the worlds most venomous animal. The injected toxin has both dermatonecrotic and cardiotoxic properties.
CIGUATERA POISONING: It is the most common poisoning accounting for 50%. Species involved are: barracudas, sea bass, parrot fish, red snapper, grouper, and amber jack. Ciguatoxin found in certain algae and protozoa are eaten by herbivorous fish, which in turn are eaten by large fish which become poisonous. It affects the gut and nervous system. Poisoning occurs after eating fresh or frozen fish prepared by boiling, baking, frying, stewing or broiling. Symptoms set in one to 12 hours are: abodminal pain with cramps, nausea, vomiting, profuse watery diarrhoea, diaphoresis, headache, trembling, dizziness, dysaraesthesias and paraesthesias, tingling and numbness of the tongue, lips, throat and perioral area, myalgias, arthralgias and weakness. Hot substances feel cold and cold substances feel hot. Death may occur due to respiratory paralysis. Treatment is symptomatic.
SCOMBROID POISONING: The species involved are: mahimahi, tuna, amberjack, albacore, bonito, mackerel, skipjack and canned fish of other types, such as sardines and pilchards. The poison is made by bacteria. All of them have a high concentration of histidine in their dark meat, which is converted to histamine. Symptoms begin in minutes to hours and subside in a few hours include headache, red itching skin over the face and body, nausea, belly pain and diarrhoea. Death is rare.
GYMNOTHORAX POISONING: The moray, conger and anguillid eels carry a ciguatoxin-like neurotoxin in their viscera, muscles and gonads. Symptoms appear in half to thirty hours. They cause neurotoxic symptoms or signs of cholinergic toxicity.
TETRODON POISONING: The species involved are: globe fish, ballon fish, blowfish, toad fish, porcupine fish, puffer fish, sun fish and blue-ringed octopus. They affect gut and nervous system. Symptoms appear in minutes to hours. They contain tetrodotoxin mainly in the skin, liver, ovary, and intestine. They cause neurotoxicity. Effects are similar to those of paralytic shellfish poisoning. Within 10 to 45 minutes muscles become weak, then paralysed. The muscles used in breathing are affected, so that the patient is unable to breathe and dies.
SHELL FISH POISONING: The species include clans, oysters, mussels and scallops contaminated by feeding on poisonous dinoflagellates. This is called paralytic shellfish poisoning because the poison affects the nervous system. They contain saxitoxin, which is a potent paralytic neurotoxin. The symptoms begin in half hour. There is nausea, vomiting, headache, numbness and tingling of the lips and mouth, spreading to the legs, arms and the whole body, muscle paralysis, causing blurred vision, difficulty in swallowing, weakness and dizziness, aching muscles, reversal of hot and cold sensations, so that cold objects feel hot. Less commonly: low blood pressure, paralysis of muscles used in breathing, so that the patient is unable to breathe and death occurs. It acts on the peripheral and autonomic nervous systems. Like curare, it effectively blocks depolarisation at the neuromuscular junction.
