Ciguatoxin is a powerful neurotoxin produced by a tiny organism, a dinoflagellate called Gambierdiscus toxicus, which lives among the algae that grow in channels on the coral reefs. Herbivorous fish feed on the algae, and carnivorous fish in turn feed on them, so the toxin accumulates in large, predatory fish like snapper, grouper, surgeonfish, and jack (all of which I saw on the menu). The ciguatoxin causes no illness in fish—they seem to thrive on it—but it is very dangerous to mammals, and to man.
