A large proportion of the ocean’s biomass consists of algae. When compared to sharks and stingrays, they might appear neither spectacular nor particularly dangerous, but appearances can be deceptive: roughly 5000 known species of algae produce potent toxins. One of these is Gambierdiscus toxicus, a dinoflagellate that produces ciguatoxin. This poison may travel a long way through the food chain—Gambierdiscus grows in association with macroalgae in coral reefs, which are consumed by herbivorous fish. When these fish are eaten by predators, the toxin accumulates and concentrates in carnivorous fish which, in turn, are captured by humans. As the toxin does not have any negative impacts on the fish, it is difficult to identify affected specimens. It is also odorless and tasteless. In humans, ciguatera fish poisoning causes symptoms like nausea, vomiting, and diarrhea, followed by sensory disturbances. Some patients experience a reversal of hot and cold sensations. There is no antidote and neurological symptoms typically persist for several weeks, while in severe cases they might lead to death, remain in a patient’s system for years, or even recur under conditions of stress. Apart from laboratory testing of samples, the best prevention is to avoid eating reef fish altogether.
Sources: Sobel, Jeremy and Painter, John, “Illnesses Caused by Marine Toxins”, Clinical Infectious Diseases, vol. 41, issue. 9, (2005): 1290–1296.
Friedman, M.A. et al., “Ciguatera Fish Poisoning: Treatment, Prevention and Management”, Mar Drugs, (2008): 456-479.
Mullins, Michael and Robert S. Hoffman, “Is mannitol the treatment of choice for patients with ciguatera fish poisoning?”, Clinical Toxicology, vol. 55, issue. 9, (2017): 947-955.