Ciguatera is a foodborne illness poisoning in humans caused by eating marine species whose flesh is contaminated with a toxin known as ciguatoxin, that is present in many micro-organisms (particularly, the micro-algae Gambierdiscus toxicus) living in tropical waters. Like many naturally and artificially occurring toxins, the ciguatoxin bioaccumulates more at higher level of the food chain, such as predator species near the top of the food chain in tropical waters, such as barracuda, moray eel, and amberjack, although many other species have been found to cause occasional outbreaks of ciguatera. Ciguatoxin is very heat-resistant, so ciguatoxin-laden fish cannot be detoxified by cooking.

Due to the localized nature of the ciguatoxin-producing micro-orgaisms, ciguatera illness is only common in tropical waters, particularly the Caribbean, and usually is associated with fish caught in tropical reef waters.

The symptoms of ciguatera are gastrointestinal distress (nausea, vomiting) followed by neurological symptoms such as headaches, muscle aches, numbness, and hallucinations. Severe cases of ciguatera can also result in hot-cold reversal, in which hot and cold sensations seem reversed.