By: Dana Sackett
|Friedman et al. 2008. (http://www.mdpi.com/1660-3397/6/3/456)|
So where do these toxins come from and how do they get into our fish? Ciguatoxins are naturally produced by microscopic algae called dinoflagellates (Gambierdiscus sp.) that are found in tropical waters around the globe. They commonly live on seaweed, recently disturbed or altered shallow water marine habitats and coral reef surfaces. Planktivorous or herbivorous fish will eat the algae or seaweed, ingesting the ciguatoxic dinoflagellates, and then pass the toxin on when they are consumed by predators; biomagnifying the toxin in top predatory fish.
Gambierdiscus toxicus. The dinoflagallate often responsible for ciguatera fish poisoning. (http://www.underwatertimes.com/news.php?article_id=47518926031)
This toxin is also very fat soluble (lipophilic) and is, therefore, found in high concentrations in the fat dense areas of a fish (e.g. skin, visceral tissue, roe). Unfortunately, this does not exclude the toxin from accumulating in muscle tissue (the part we like to eat) and there are no cooking or preparation methods that can remove it.
|Growth rates of six species of Gambierdiscus measured in the laboratory at
temperatures from 18 °C to 33 °C (Tester et al. 2010).
Ciguatera is generally a concern when eating tropical species, such as grouper, triggerfish, lionfish, amberjack, barracuda and others. However, this may not be the case in the years to come. Researchers have linked high water temperatures with greater distributions and abundances of ciguatoxic algae. These results concern fishery scientists because rising ocean temperatures may result in greater geographical ranges and higher growth rates.
Because of this concern, Tester et al. (2010) examined growth rates of ciguatoxic algae and the number of poisoning events in the Caribbean and West Indies in relation to sea surface temperature. Their research found that high temperatures (>29oC) that last an extended period of time were correlated with high algae growth rates and increased ciguatera poisoning events.
|Average ciguatera fish poisoning incidence rates per 10,000 population per year from 1996–2006 across the Caribbean, plotted with temperature contours (°C) from annual average sea surface temperatures from 2002–2007 (Tester et al. 2010).|
Other research has shown that high water temperatures can increase ciguatera in other ways too. Tyler Smith and his students in the Virgin Islands found that ciguatoxic algae, which secrete mucus to attach to their environment, are unable to attach to live coral. They suggest that massive coral death (due to coral bleaching from warmer water temperatures or dredging) could provide more habitat for the toxic algae and again result in more infected fish and thus more human poisoning events.
|Picture of a great barracuda, often contaminated with ciguatoxin
because of its role as reef apex predator.
Just a few weeks ago, an innovative approach at understanding ciguatera in relation to fish ecology was published in Science of the Total Environment (O’Toole et al. 2012). They associated fish movements (using acoustic telemetry) with the accumulation of ciguatoxins in great barracuda (Sphyraena barracuda). Their results suggest that those fish that were less mobile and stayed within relatively small areas on the western side of Cape Eleuthera had higher concentrations of ciguatoxins.
Receiver stations where telemetered barracuda, with and without ciguatoxin,
were detected near Cape Eleuthera, The Bahamas (O’Toole et al. 2012)
This study helps to answer the question of whether ciguatoxins are accumulated in fish locally or elsewhere by migratory fish that move into local areas. Little information is known about the conditions that support toxic algae growth and the pathway of accumulation in fish. This information is needed to prevent poisoning events. In addition, for many contaminants that can biomagnify through aquatic food webs, changing environmental conditions require us to understand the link between toxin sources, fish movements, and food web structure to prevent future poisoning events.
Friedman MA, Fleming LE, Fernandez M, Bienfang P, Schrank K, Dickey R, Bottein M-Y, Backer L, AyyarR, Weisman R, Watkins S, Granade R, & Reich A. 2008. Ciguatera Fish Poisoning: Treatment, Prevention and Management. Marine Drugs 63:456-479.
Lewin A. 2010. Discussions focus on ciguatera poisoning. Virgin Islands Daily News. http://virginislandsdailynews.com/discussions-focus-on-ciguatera-poisoning-1.1075699
O’Toole AC, Bottein M-Y D, Danylchuk AJ, Ramsdell JS, & Cooke SJ. 2012. Linking ciguatera poisoning to spatial ecology to fish: A novel approach to examining the distribution of biotoxin levels in the great barracuda by combining non-lethal blood sampling and biotelemetry. Science of the Total Environment. http://www.sciencedirect.com/science/article/pii/S0048969711013684
Tester P, Feldman RL, Nau AW, Kibler SR, & Litaker RW. 2010. Ciguatera fish poisoning and seasurface temperatures in the Caribbean Sea and the West Indies. Toxicon 56:698-710. http://www.sciencedirect.com/science/article/pii/S0041010110000978
Underwater Times. 2012. Marine Scientist Awarded Grant To Study Ciguatera Fish Poisoning; ‘There’s A Lot We Don’t Know.’ http://www.underwatertimes.com/news.php? article_id=47518926031