As we wrote in last month’s issue, brass-eating fish are not the cause of ciguatera aka fish poisoning, or gratte, as ciguatera is called in many areas of the world. Ciguatera is caused by eating fish that are contaminated with Ciguatoxin or Maitotoxin, two of the most lethal, naturally-occurring toxins, considered more toxic than arsenic.
Microscopic alga known as dinoflagelates, specifically Gambierdicus toxicus, found living on tropical and sub-tropical dead coral are the hosts of Ciguatoxin. According to the literature found in the library at the U.S. National Museum of Natural History, Gambierdicus toxicus was first identified in the Gambier Islands in the Pacific around 1979. It was also identified around Hawaii in 1979, the U.S. Virgin Islands in 1985, and the Florida Keys in 1981; however, it has been present in the tropics and affecting peoples’ lives for far longer.
There is some evidence that Alexander the Great refused to allow his troops to eat fish for fear of fish poisoning. Captain William Bligh described an outbreak of ciguatera among his sailors in 1789. A Portuguese biologist, Parra, first gave fish poisoning its official name, ciguatera, around 1771.
While all involved in the study of ciguatera and world-wide health agencies agree that the reporting of cases is incredibly lax among countries in the tropics and sub-tropics where ciguatera is present, they estimate that approximately 50,000 people per year are infected. Many scientists believe the incidence is much higher because many sufferers do not seek treatment and there are those that believe some countries deliberately do not report cases for fear of scaring away travelers. Under or non-reporting coupled with a medical profession that often is not always knowledgeable about ciguatera are good indicators that the incidence of ciguatera may be much higher.
After speaking with scientists attempting to obtain accurate medical records of ciguatera poisonings in the Caribbean with little success, met with resistance when requesting those records with no explanations given, I spoke with employees working at a hospital emergency room. Because they were concerned for their jobs, they would not consent to official interviews. One, however, was adamant that he had seen several cases in the ER over one six-month period in 2006 yet that hospital would not co-operate with the scientists attempting to develop predictors for ciguatera outbreaks. This employee also stated that he had never heard of ciguatera prior to arriving in the Caribbean, no mention made during his medical training.
So…what fish carry ciguatera? There are over 400 species throughout the tropical and sub-tropical zones. Not only are alga-eating fish carriers but also their predators. Some of the more common carriers are certain species of grouper, snapper, parrotfish, eels, King mackerel, and Greater amberjack. Barracuda seem to be at the top of the list since they feed upon many species of the reef fish. As the reef food chain moves upwards, fish feeding upon smaller fish that feed upon yet smaller fish, each step up the ladder increases the amount of toxin carried as the loads of toxin are cumulative.
While there is no accurate way to test for ciguatera before eating a fish other than submitting the fish to complicated biological studies done in laboratories, avoiding the consumption of reef fish and their predators when ciguatera is present is recommended. But how does one know if ciguatera is present?
Scientists are currently working to develop predictors based on several factors including time of year, currents, storm patterns, water temperature, monitoring the health of reefs and corals, and medical statistics. Due to the previously mentioned lack of accurate medical statistic reporting, the development of predictors will be a long process.
In the meantime, recommendations include knowing from where and by whom the fish are taken. Local fishermen whose livelihood depends upon providing safe, quality fish have knowledge of where, when, and what species of fish to catch based on history. That said, there seems to be emerging evidence that toxic fish may move by choice or be forced to move by strong tropical storms so an area that was safe one day may be unsafe a day or two later.
Not eating fish caught in lagoons and pools where water movement is very slow or even stagnant is also a recommendation. Avoiding the consumption of reef fish from areas of known coral die-off is another. And, know your fish; consumers have become ill when an unscrupulous chef or fisherman has substituted dog snapper for mahi or wahoo…know what the fish ordered should look and taste like. Or, avoid eating reef fish and, particularly, barracuda, altogether, and eat only deep water species.
Know the symptoms of ciguatera and the recommended treatment in case the medical provider is uninformed. Within 10 minutes, up to 24 hours, of eating fish, should symptoms occur (including vomiting, pain, dizziness, temperature reversal, tingling/numbness, and muscle cramping), seek immediate medical attention. While there is no cure for ciguatera, intravenous mannitol given within the first few hours can lessen the multiple symptoms in some patients. Symptomatic treatment with the administration of medications for relief of pain, nausea, and careful monitoring of vital signs as well as monitoring for complications while the victim recovers is the only protocol available.
As a service to our readers, we have included a pull-out poster in the center of this month’s issue of All At Sea. We hope you will keep the pull-out as a reference and that it keeps you safe as you continue to enjoy eating what is generally one of nature’s most healthy foods.
After 30 years as a wild and domestic animal rescuer, rehabber, and educator in the states, Becky Dayhuff became a scuba instructor and award-winning journalist covering the marine environment in the Caribbean. She is a contributing photographer to NOAA.