Have you ever seen this warning on books, magazines or other media? It can apply to a few hundred tropical and subtropical reef fish (possibly over 400 according to some references) including some very popular aquarium species. You may even have some of these fish in your aquarium right now.
If you have no idea what ciguatera poisoning is, you aren’t alone. Even some TFP employees that I mentioned this blog topic to had no idea what “ciguatera poisoning” was even though they have seen the term before and we deal with these fish every day. Is it something that, as aquarists, should be worried about? No….and yes. Ciguatera poisoning is food-borne. As long as you don’t make a regular habit of eating fish from your aquarium, you aren’t going to contract it at home. But, if you eat fish regularly, it may a concern and certainly deserves more awareness than it is given.
The fish that cause ciguatera poisoning are usually predators at the top of the food chain, but the toxin itself comes from the bottom – tiny planktonic organisms known as dinoflagellates. Dinoflagellates are found in freshwater and saltwater, organisms responsible for the notorious “Red Tides” that bloom in some waterways. Zooxanthellae, the algae living within and providing food to the tissues of corals, are also dinoflagellates. The dinoflagellates that are responsible for ciguatera poisoning are related to and may even be the same as those thriving your corals right now. These dinoflagellates are from tropical and subtropical waters (around and between the Tropics of Cancer and Capricorn, including the equatorial region), including the areas of the Indian, Pacific and Atlantic Oceans that supply many fish for aquariums and seafood industries. The most notorious of these dinoflagellates, Gambierdiscus toxicus, along with others produce toxins like palytoxin (the toxin that makes some Zoanthid and Palythoa polyps potentially hazardous) and ciguatoxin, the toxin we’re focusing in in this article.
Dinoflagellates producing these toxins live in or cling to algae and corals, especially corals that may have been damaged, according to some recent research. The dinoflagellates are eaten by herbivorous, grazing fish, which are eaten by larger fish, which are eaten by larger fish and so forth up the food chain. This is a process known as bio-accumulation. The higher up the food chain a fish is, the more dinoflagellates accumulate in their own tissue from all of the fish they have eat. Fish like groupers, snappers, jacks, barracudas, moray eels and parrotfish are some of the fish most affected by this bio-accumulation and tend to have the highest levels of ciguatoxin in their flesh. These also happen to be some of the fish most commonly found on menus, here and abroad.
Avoiding Ciguatera Poisoning
“Just cook it and don’t eat raw fish, and its fine, right?” Nope. Ciguatoxin can’t be neutralized by heating or freezing. It doesn’t change the taste, look or odor of the fish (living or dead). It isn’t dangerous to the fish. There are no ways to test for it (other than complicated laboratory tests on the flesh, which are still fairly unreliable). It affects fish from an incredibly broad region (mostly the Pacific Ocean and the Caribbean) and can even be found in some farm-raised salmon. The only way to avoid it is to avoid any fish from these regions that are known possible carriers. Reports have also shown that the toxins can be sexually transmitted or passed through breastfeeding.
Symptoms and Treatment
How do you know if you have ciguatera poisoning? It is uncommon in the United States and most Americans who suffered from it acquire it while vacationing in the Caribbean or on tropical islands abroad. Symptoms usually start less than an hour after the meal and are pretty typical of what we think of as food poison –nausea, vomiting, diarrhea. The list of possible symptoms of ciguatera poisoning go far beyond this however. They are shared by other conditions like Multiple Sclerosis and can be neurological (numbness in arms and legs, dizziness, confusion, loss of balance, hallucinations) and cardiological (increased or lowered blood pressure, irregular heartbeats) as well as gastrointestinal (nausea, vomiting, diarrhea, cramping and severe abdominal pain). As a result, ciguatera poisoning is often misdiagnosed. The tell-tale symptom that tends to lead to a ciguatera diagnosis is one of the most bizarre – the seeming reversal of hot and cold. Hot things feel painfully cold and cold things feel burning hot.
There is no known cure for ciguatera poisoning. Some medications have been used to treat the symptoms but their effectiveness is questionable. The symptoms may disappear over time but may takes weeks or even years, and may come back with some triggers like nuts, alcohol, or exercise.
Rethinking tonight’s dinner plans yet? When I started researching for this blog, it was just intended to be a brief informational entry about a common term you may come across. All I really knew about ciguatera poisoning was that it was a type of food poisoning from predatory fish. Now, after researching the topic more, most of us in aquatic sciences here at TFP are taking a closer look at our seafood-heavy diets. Sure, there’s salmonella poisoning and mad cow disease and a slew of other food concerns, but awareness is the first step. Next time you are standing by the seafood case or glancing at a restaurant’s menu, try checking into the source of that snapper or grouper filet.
Ciguatera poisoning overview
Moray Eelimage referenced from wikipedia and originally posted by NHobgood
Grouper and shark image referenced from wikipedia and originally posted by Albert Kok