Beware of Toxic Fish

unicornfishMore than 400 species of tropical reef fish, including wrasses, snappers, groupers, jacks, moray eels, surgeonfish, shellfish, and especially barracudas are known to cause seafood poisoning (ciguatera). There’s no way to tell if a fish will cause ciguatera: a species can be poisonous on one side of the island, but not on the other.

In 1976 French and Japanese scientists working in the Gambier Islands determined that a one-celled dinoflagellate algae or plankton called Gambierdiscus toxicus was the cause. Normally these microalgae are found only in the ocean depths, but when a reef ecosystem is disturbed by natural or human causes they can multiply dramatically in a lagoon. The dinoflagellates are consumed by tiny herbivorous fish and the toxin passes up through the food chain to larger fish where it becomes concentrated in the head and guts. The toxins have no effect on the fish that feed on them.

French Polynesia’s 700 to 800 cases of ciguatera a year are more than in the rest of the South Pacific combined, leading to suspicions that the former French nuclear testing program is responsible. Ciguatera didn’t exist on Hao atoll in the Tuamotus until military dredging for a 3,380-meter runway began in 1965. By mid-1968 43 percent of the population had been affected. Between 1971 and 1980 more than 30 percent of the population of Mangareva near the Moruroa nuclear test site suffered from seafood poisoning. Yet ciguatera has been around for a long time, having been reported in New Caledonia by Captain Cook.

The symptoms (numbness and tingling around the mouth and extremities, reversal of hot/cold sensations, prickling, itching, nausea, vomiting, erratic heartbeat, joint and muscle pains) usually subside in a few days. Induce vomiting, take castor oil as a laxative, and avoid alcohol if you’re unlucky. Symptoms can recur for up to a year, and victims may become allergic to all seafood.

Avoid biointoxication by cleaning fish as soon as they’re caught, discarding the head and organs, and taking special care with oversized fish caught in shallow water. Small fish are generally safer. Whether the fish is consumed cooked or raw has no bearing on this problem. Local residents often know from experience which species may be eaten.