Ciguatera on the agenda

tropicalities

Ciguatera on the agenda at Papeete congress

Ciguatera fish poisoning was one of the subjects discussed by experts from all over the world at the fifth International Coral Reef Congress in Papeete from May 27 to June 1.

This type of fish poisoning occurs throughout the Pacific, Caribbean and Indian Ocean regions, indeed in all areas where there is live coral reef.

Known for centuries in the Pacific region, on some islands certain fish were traditionally tabu, as the outbreaks of ciguatera were a great mystery.

Over 400 species of fish have been incriminated at different times, one kind being toxic in one area but not in another, even within the same lagoon.

This is the essence of the problem, as there is no way of telling which fish are poisonous.

This factor also probably accounts for the continuing high incidence of cases of fish poisoning for instance on average 1000 cases per year in French Polynesia alone.

One of the leading authorities on ciguatera is Dr Raymond Bagnis, head of the Medical Oceanographic Research Unit at the Louis Malarde Institute in Papeete. Dr Bagnis led the team which several years ago identified the culprit as a tiny plant similar to a micro-algae.

Normally only a few of these algae live on the reef, but under certain circumstances their number can suddenly increase.

Fish such as the surgeon or parrot fish feed on these toxic algae and so it enters the food chain. These grazing fish usual ly live and feed in one area, so they gradually absorb more and. more toxin. A predatory snap per or grouper then comes along and with one bite ac quires all the toxicity that its

herbivorous victim has spent its life collecting. These larger fish can then carry the toxicity to other parts of the reef.

For the last 20 years, all cases of ciguatera fish poisoning in French Polynesia have been recorded in detail. By studying these, as well as examining older records, Dr Bagnis and his team have been able to draw some interesting conclusions.

In every outbreak of ciguatera, some disturbance or damage to the coral reef had occurred in the previous year or two. Sometimes this was caused by a naturally occurring event such as a storm or a cyclone. But more often it was due to man’s interference with the coral ecosystem.

This damage to the coral can be caused by such activities as blasting a channel or pass through the reef, building quays or breakwaters on live coral, or dumping metallic materials or other polluting debris on the reef. Whether the coral is de stroyed by man or by natural causes, the toxic micro-algae loves to multiply on new ex posed coral surfaces, and so the cycle begins.

Not everyone eating ciguato xic fish shows the same symp toms, but usually vomiting, sto mach pains and diarrhoea occur within a few hours. Prick ling in the fingers and toes, plus a tingling around the mouth, are ch«- 'acteristic symptoms of ciguatera poisoning. An altera tion of sensation causes plain

water to taste like soda, and a shower to feel like pin pricks or tiny electric shocks. A feeling of great tiredness can make walk ing difficult as though the pa tient is paralysed. In serious cases the pulse slows, the blood pressure falls and occasionally in very severe cases death may occur from respiratory para lysis. In most cases however the symptoms subside within a few days, although the tingling can continue longer, as does an increased sensitivity to fish.

There is no cure for ciguatera poisoning except to relieve the symptoms. The most successful therapy is the intravenous injection of calcium glutonate, together with Vitamins B 6 and 812. This appears to work by preventing the toxin entering

Dr Raymond Bagnis . . . the quest for a ciguatera antidote.

the cells of the body where it has its effect.

Although the causes of ciguatera are well known, the various research teams throughout the world are still searching for a quick test of toxic fish and an antidote for the poison. The main stumbling block is the nature of the poison itself, one of the most active known to man, even more than the most poisonous snake venom. It takes up to 10 tons of poisonous fish to extract just a few micrograms of the main substance, ciguatoxin, for use in laboratory experiments. All re search work at present is con centrating on finding out the exact chemical structure of this minuscule ciguatoxin. Once that is known, it may be pos sible to synthesise it and pre pare an antidote.

As few islanders want to exclude fish from their diet, and the majority of fish are quite safe to eat, Dr Bagnis suggests various ways that the risks can be minimised.

The poison is concentrated in head, liver, roe and intestines, so the most important precau tion is not to eat these organs.

The fish should be gutted and the viscera thrown away as soon as possible after catching, taking care not to puncture the viscera. The sauce, juice or soup that comes from cooking the fish should never be eaten, as some of the poison is ex tracted and concentrates in the cooking liquid. All oversize fish are particularly likely to be ciguatoxic, and large snappers, groupers, wrasses, jacks, barra cudas and moray eels are very suspect. The most commonly toxic fish in the Pacific region is the red snapper. In French Polynesia the 10 most suspect species have now been prohi bited from sale in the market.

As the toxicity is directly related to the amount eaten, it also pays to eat modest quantities of an unknown fish.

Meanwhile one message is clear: every outbreak of ciguatera indicates that some thing is wrong on the reef, usually that man has been interfering with the living reef, an action for which nature is making him pay a certain price.

Gwenda Cornell in Papeete.