Ciguatera toxin tends to accumulate in large predator fish (weight over 2 Kg or about 4.5 lbs), such as the barracuda and other carnivorous reef fish, because they eat other fish that consume toxin-producing algae (dinoflagellates), which live in coral reef waters.he toxin has highest concentrations in fish visceral and sex organs. Ciguatera toxin is harmless to fish, but poisonous to humans. The toxin is odorless and tasteless, and cooking does not destroy the toxin. Eating ciguatera-contaminated tropical or subtropical fish is the main way that humans are exposed to the toxin.