Giant clams. Giant clams: could they represent a new vector of Ciguatera ?

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Roué, M. | Picot, S. | Ung, A. | Viallon, J. | Sibat, M | Amzil, Z. | Gaertner-Mazouni, Nabila | Chinain, M. | Darius, Ht.

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International audience. Ciguatera Fish Poisoning (CFP) is a form of ichtyosarcotoxism caused by the consumption of tropical coral reef fishes that haveaccumulated ciguatoxins (CTXs), neurotoxins produced by dinoflagellates of the genus Gambierdiscus. However, giant clams,frequently consumed in the South Pacific, are sometimes also involved in strong and atypical Ciguatera incidents, as observed inFrench Polynesia, New Caledonia and Vanuatu. To evaluate the ability of giant clams to accumulate CTXs in their tissues, in vitrocontamination experiments were conducted. When fed 10 times per day for up 2 days with 2,000 cells.l -1 (for a total of 40,000cells.l-1) of a highly toxic strain of Gambierdiscus polynesiensis (containing 7.5 eqv pg P-CTX-3C.cell-1), giant clams appeared toxicby cell based assays (CBA), with a mean of 11.23 eqv ng P-CTX-3C.g-1 wet weight. However, giant clams fed with the sameconcentration of a non toxic strain of Gambierdiscus toxicus were found non toxic on Neuro-2A cells. When giant clams were fedwith lysed cells of G. polynesiensis or G. toxicus, similar results were obtained using CBA. These results will be completed by liquidchromatography mass spectrometry (LC-MS/MS) analysis in order to confirm the identity of the toxins accumulated. These firstobservations indicate that giant clams are able to fix CTXs and could thus constitute another pathway in the ciguatera food chain.This study should contribute to the improvement of seafood poisoning risk assessment and management programs in ciguaterapronecoral reef regions worldwide.

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