Another Reason Not to Eat Shark (Meat)

Shark meat consumption is bad for sharks of course, millions of sharks are killed each year for the shark meat and fin trade, but it’s also bad for people.  I’ve written before about the way heavy metals and organic pollutants like PCBs concentrate in animals high up on the food chain.  Shark meat has been shown to carry levels of toxic metals such as mercury that far exceed what is allowable for human consumption.  A recent article demonstrates that sharks can also carry the dangerous and often fatal marine toxin ciguatoxin.  Eating a single piece of ciguatoxin-contaminated fish can be lethal for humans, and in the case described in this paper it caused the death of 11 people in Madagascar who ate the meat of a contaminated bull shark.

Ciguatoxin is produced by certain types of algae, which are consumed by fish and then become concentrated in higher levels of the food chain.  The disease that results in humans is called ciguatera fish poisoning (CFP).  Large predatory fish that eat ciguatoxin-contaminated prey can carry extremely high levels of the toxin, and tens to hundreds of thousands of human poisonings each year come from contaminated reef fish such as mahi-mahi, grouper, snapper and others.  Ciguatoxin is not destroyed by heat, so contaminated fish remain toxic even after cooking.  Symptoms of CFP are initially gastrointestinal (nausea, vomiting), and neurological (tingling of the lips and fingers), and eventually cardiac (irregular heartbeat, heart failure).  In survivors of the initial poisoning, the neurologic symptoms can persist for months.

Shark should be added to the watch-list for CFP.  In the Madagascar incident, 97 people became sick after eating the meat or liver of a bull shark.  Eleven of those who became sick eventually died.  Genetic analysis of remaining samples of the meat consumed showed that it all came from a single bull shark.  Mass spectrometry analysis was used to show the presence of ciguatoxin in the meat of the shark, and very high levels in the stomach.  To confirm the potency of the toxin as the cause of death, mice injected with an extract from the remaining shark meat samples died within hours.

So don’t eat sharks.

The article is: Diogene J, Reverte L, Rambla-Alegre M, del Río V, de la Iglesia P, Campos M, Palacios O, Flores C, Caixach J, Ralijaona C, Razanajatovo I, Pirog A, Magalon H, Arnich N and Turquet J. (2017) Identification of ciguatoxins in a shark involved in a fatal food poisoning in the Indian Ocean. Scientific Reports, 7:8240. DOI: 10.1038/s41598-017-08682-8.