Poisonous Reef Fishes

Several kinds of reef fishes are poisonous to eat. This page describes two types of poisonous or potentially poisonous fish.

Tetradotoxic             Ciguatoxic

Tetradotoxic

Porcupinefish / Buteten tituka' / Diodon hystrix
Images from Coral Reefs CD

Buteti (puffers) and buteten tìtuka'(porcupine fishes) produce an extremely toxic substance called tetrodotoxin. Dånglon and toriyu(boxfishes) and tripletooth puffers might also produce this poison, but more research needs to be done. Tetrodotoxin is usually concentrated in the internal organs and skin, but the flesh may also be toxic. The toxin is one of the most powerful poisons known and a very small amount can cause death. Some people eat the flesh of puffers, but that is a very dangerous practice. The toxin cannot be destroyed by cooking or any other process. The toxin causes the skin of these fishes to taste bitter so predators will avoid them. Puffers also can make themselves larger and harder than normal by inflating themselves with water. This also makes it harder for a predator to eat them. An inflated spiny puffer is nearly impossible to eat. Boxfishes also produce a substance that makes them taste bad. This poison is released from the skin when the boxfish becomes frightened or stressed and can kill other fishes in the same bucket or aquarium as the boxfish. It is not yet known whether the poison from boxfishes is the same as tetrodotoxin.

Puffers, porcupinefishes, and boxfishes eat a variety of plants and bottom-dwelling animals like mollusks, crustaceans, sea urchins, starfishes, and worms. Some have broad diets while others specialize on certain things. Some puffers for example, feed mainly on tips of branching corals. Most of these fishes are slow swimmers since they have little to fear.

Ciguatoxic

Giant moray eel / Titoghe / Gymnothorax javanicus

Several kinds of reef fishes may contain toxins that can produce symptoms called ciguatera. There are several neurotoxic substances which affect the nervous system. Ciguatoxins are produced by a tiny single-celled organism called dinoflagellates. The dinoflagellates colonize bare surfaces of the reef as well as man-made surfaces or even blades of seagrass. They are eaten with filamentous algae by herbivorous fishes which are in turn, eaten by predatory fishes. The toxins are not metabolized, but accumulate in the body tissues and become most concentrated in the liver and reproductive organs. Each time a predator eats a smaller fish, it accumulates its victim's lifetime accumulation of ciguatoxins. Consequently, large predatory fishes tend to have the highest concentrations of ciguatoxins and are the most likely to cause ciguatera poisoning.

More information on ciguatera in the food chain.

On Guam, large tagåfi (red snapper) and large titohge (moray eels) are frequently toxic and should NEVER be eaten. Occasionally, large individuals of other kinds of reef fishes such as gådao (groupers), ålu (barracudas), mamulan (jacks), lililok (emperors), or pulonnon (triggerfishes) may be toxic and should be avoided. The liver and other internal organs of any reef fish should never be eaten. Fortunately, ciguatera is not found in deepwater or pelagic fishes, that is, those caught below 400 feet (122 m) or in the open sea away from the reef.
Symptoms of ciguatera range from a tingling of the lips to reversal of the sensations of hot and cold, muscular weakness, vomiting, diarrhea, shortness of breath and cardiac arrest. Death is rare, but the sickness can last for months. Anyone suspected of suffering from ciguatera should seek medical care immediately.

Giant coral grouper / Gadao / Plectropomus laevis

Twinspot snapper / Tagåfi / Lutjanus bohar