Map
of ciguatera areas (Centre d'océanologie de Marseilles.)
"La gratte"
The name "gratte" is employed in New Caledonia and in all French overseas tropical territories. The scientific name is "ciguatera". Ciguatera is transmitted to man through consumption of fish from coral reefs areas and from the lagoons.
Ciguatera is endemic in almost all the tropical regions with coral reefs and thus in New Caledonia.
Origin
Coral killed through various causes such as pollution, rising temperatures, etc. is then colonised by algae ( Halymenia sp., Portieria sp., Turbinaria sp. and Sargassum sp. etc. ) which host dinoflagellates. Dinoflagellate generate toxins, the main one, giving ciguatera, being the ciguatoxine.
Plant eating fish such as the surgeon fish and coral eaters such as the parrotfish ingest the toxin which is then passed on along the food chain. It gets best concentrated into the large predatory fish such as moray, golden trevally, groupers, and barracuda. The fisherman is at the end of the chain. Even crustacean and shells may get infected but this seems quite rare.
The ciguatera toxin is not destroyed by cooking or freezing. The toxic fish flesh has no peculiar taste. The toxin does not change the tasting qualities of a fish.
Symptoms and diagnosis
Ciguatera symptoms occur a few hours only after consuming the fish. They are akin to food poisoning with diarrhea, vomiting, headaches. They are sometimes accompanied by a lower blood pressure and weakening which may last several days. More enduring symptoms are intense itching, joint and muscle pain, burning or itching when cold liquids are touched or under showers. They are intensified or reactivated through consumption of alcoholic beverage or through eating fish again, even safe or tinned.
Some people very sensitive to toxins may develop grave illness with an anaphylactic reaction.
Symptoms may last up to 2 to 3 months.
Treatment
Treatment is generally supportive and includes antihistamines, calcium gluconate, pyridoxine, corticosteroids, atropine and vitamin B.
Mannitol treatment can be used for graver cases and is carried-out in hospital environment.
Traditionally in New Caledonia, herb teas of various plants are used for treatment. Some preparation of the traditional medicine seem to have some efficiency. Preliminary results of studies conducted by the IRD (ex Orstom) research center have confirmed the activity of some species such as the "faux tabac" (argusia argentea) and "faux poivrier" (schinus terebenthifolius). L' IRD has established a list of some 100 plants from New Caledonia and Vanuatu known to treat ciguatera but many have yet to be scientifically tested.
In any case it is recommended to drink a lot of water to help the toxin elimination. Thus herb teas from some plants such as the "liane jaune" would give good results perhaps because of their diuretic effects. On the other hand consumption of alcoholic beverage or eating fish must be avoided for several months.
Detecting potentially toxic fish
Presently, there is no commercial assay available to test potentially toxic fish. A test kit is sold by Oceanit Test Systems, Inc. but we do not know whether it is effective.
In New Caledonia numerous practical tests are used but their reliability is doubtful. The most well known consists in placing pieces of the fish to be tested , the liver for instance, on an ant bed. The ants are supposed to die if the fish is toxic. Pets friends would frown upon another test, said to be the most efficient, and which consists in giving some part of a suspected fish to your cat. Cats are said to be very sensitive to the toxin and the test would be fatal to them if the fish is toxic.
Theoretically any fish from the lagoon could be toxic. In fact the potentially toxic ones are the predatory fish among the eldest, thus the biggest. To make a list of the generally toxic fish or, better, the ones which have the reputation of never giving ciguatera, you should consult local people. A lot of lagoon and coral fish is eaten in New Caledonia and ciguatera cases are not that frequent. Local experience must have some interest.
Fish from outside the lagoon are not ciguatera toxic (tuna, marlin, jobfish, dolphinfish) and you can eat them without fear. These are the ones mostly served for safety reasons in Noumea restaurants.