[Analysis of Ciguatoxins in Variola louti Captured off the Ogasawara (Bonin) Islands]

Ciguatera poisoning (CP) is one of the most abundant seafood poisonings in the world. CP frequently occurred in the tropical and subtropical Indo-Pacific Ocean and the Caribbean Sea. In Japan, CP cases have been reported annually, from the subtropical regions, including Okinawa Prefecture and Amami Islands, Kagoshima Prefecture. The principal toxins, named ciguatoxins (CTXs), are bio-synthesized by benthic dinoflagellate of genera Gambierdiscus and Fukuyoa. They are bio-transferred herbivorous animals to carnivorous fishes via the food chain.The Ogasawara Islands comprise more than 30 islands, Mukojima Islands, Chichijima (Bonin) Islands, Hahajima Islands, Iwo Islands, Nishinoshima, Minamitorishima, and Okinotorishima, which locate in the tropical to subtropical regions. The Mukojima Islands, Chichijima Islands, and Hahajima Islands locate approximately the same latitude as Okinawa. The distance from Tokyo is approximately 1,000 km for Chichijima, 1,700 km for Okinotorishima (the southernmost tip of Japan), and 1,900 km for Minamitorishima (the easternmost tip of Japan). These islands exist in a wide range of waters, latitudes from 20°25' to 27°44' North and longitudes from 136°04' to 153° 59' East. We collected 65 specimens of a grouper, Variola louti, the most frequent species implicated in CP in Japan, from the waters around the Chichijima, Mukojima, and Hahajima islands. The fish flesh specimens were analyzed CTXs using the liquid chromatography-tandem mass spectrometer (LC-MS/MS). While the peak whose retention time is almost identical to that of CTX1B was detected in all specimens on our routine protocol, no 52-epi-54-deoxyCTX1B nor 54-deoxyCTX1B was detected. The peak retention time was quite different from that of CTX1B when re-analyzing by changing the analytical column. Thus, the CTXs in the specimens in the waters of these islands seemed to be undetectable levels.