MARINE POISONS
A number of marine organisms are poisonous to humans. These can be divided into those which are poisonous when eaten and those which are venomous, either stinging or injecting poison.
Ciguatera poisoning is caused by eating fish which have consumed toxic algae which colonise damaged coral reefs. Herbivorous fish graze on the algae, which is incorporated into their tissues, although it causes no damage to them. Carnivores eat the herbivores and the toxin is concentrated in their tissue. Eating large carnivorous species of tropical fish, such as Spanish mackerel, barracuda, snapper and trevally, can expose humans to ciguatera poisoning.
Within 12 hours of ingestion the sufferer may experience general weakness, aching limbs, tingling in hands, feet and lips, itching in the palms of the hands and soles of the feet, reversal of hot and cold sensations, chest tightness, headache, toothache and convulsions. In severe cases, death can result. If the poisoning is recognised within six hours, vomiting should be induced. In any case medical attention should be sought urgently. In order to prevent exposure to ciguatera poisoning, fish should be eaten with caution.
A number of plankton-eating fish and bivalves (such as clams, mussels, abalone and shellfish) can accumulate high concentrations of toxins by feeding on toxic red-tide microalgae without harming themselves. Birds, fish, crabs, other animals and humans consuming such animals are affected by these toxins. Paralytic shellfish poisoning is caused by neurotoxins which can cause nausea, loss of balance, defective vision and, in severe cases, convulsions and death due to muscle paralysis. Diarrhoetic shellfish poisoning causes abdominal pain, diarrhoea, nausea and vomiting. Symptoms develop within a few minutes to a few hours of eating contaminated fish or bivalves. Amnesic shellfish poisoning causes vomiting, diarrhoea, abdominal cramps and permanent memory loss due to the loss of brain cells. Fortunately none of these forms of poisoning is common. However, increasing pollution of our coastal waters by nutrients from sewage outfalls may lead to increased outbreaks of shellfish poisoning. In countries where reported outbreaks have taken place, it is part of fisheries management practice to regularly monitor microalgae and make random checks of shellfish tissue.
A number of marine animals have venomous stings. These include jellyfish (see Bites and Stings).
The blue-ringed octopus is well-known for its venomous bite. Found in the southern coastal waters of Australia, the blue-ringed octopus is rarely seen because it has a span of only 12 cm, moves very fast and has excellent
camouflage. It also has a habit of hiding in discarded cans and bottles, dead gastropod shells or clumps of mussels.
Another animal with a poisonous bite is the cone shell, an oblong smooth dark brown shell with white markings, approximately 10-15 cm long. The following remarks apply to both animals. The initial bite is rarely felt. There may be slight bruising, but otherwise the wound is hard to see. Symptoms are numbness, nausea, visual disturbances, speech impairment, numbness of tongue and breathing difficulties. Paralysis may develop rapidly with respiratory failure, in severe cases within one hour. Medical aid should be sought urgently. Before paralysis sets in, the bite should be washed and a firm bandage placed all the way up the affected limb. The patient should be rested on her or his side. Following paralysis, EAR (mouth-to-mouth resuscitation) should be applied, and in advanced cases cardio-pulmonary resuscitation may be needed.
Some fish, such as stonefish and bullrout have stinging spines which may inject poison when disturbed by humans. It is therefore advisable to wear protective footwear when walking on rocks on the shore or wading in deep water or on mud flats. Symptoms include immediate intense pain at the site of the puncture, followed by the spread of pain along the limb and swelling. The stinging spine may be present in the wound and the area sometimes turns grey or blue. Sweating, shock and irrational behaviour can also be signs. Medical aid should be sought urgently. The affected part should be placed in very warm fluids and foreign bodies should be removed if they come away easily. Mouth-to-mouth resuscitation may be necessary if breathing stops.
Stingrays also have stinging spines halfway along their tails which can inflict painful wounds. Since these animals often lie submerged in the sand, care should be exercised when wading. The injection of a stingray’s barb will cause immediate intense burning pain, bleeding and possible difficulty in breathing. The barb should be gently extracted if visible and the wound bathed with hot water. Medical aid should be sought.
*3\69\2*
