Ciguatera fish poisoning (CFP) is one of the most frequently reported seafood poisoning diseases. It is endemic to the tropical region and occurs most commonly in the regions around the Pacific Ocean, Indian Ocean, and Caribbean Sea. The principal toxins causing CFP are ciguatoxins (CTXs). In the Pacific region, more than 20 analogs of CTXs have been identified to date. Based on their skeletal structures, they are classified into CTX1B-type and CTX3C-type toxins. We have previously reported species-specific and regional-specific toxin profiles. In this study, the levels and profiles of CTXs in fish present in the tropical western Pacific regions were analyzed using the liquid chromatography–tandem mass spectrometry (LC–MS/MS) technique. Forty-two fish specimens, belonging to the categories of snappers, groupers, Spanish mackerel, and moray eel, were purchased from various places such as Fiji, the Philippines, Thailand, and Taiwan. Only the fish captured from Fijian coastal waters contained detectable amounts of CTXs. The toxin levels in the fish species found along the coastal regions of the Viti Levu Island, the main island in Fiji, and the toxin profiles were significantly different from those of the fish species present in other coastal regions. The toxin levels and profiles varied among the different fish samples collected from different coastal areas. Based on the toxin levels and toxin profiles, the coast was demarcated into three zones. In Zone-1, which covers the northern coast of the main island and the regions of the Malake Island and Korovau, CTXs in fish were below the detection level. In Zone-2, CTX3C-type toxins were present in low levels in the fish. CTX1B-type and CTX3C-type toxins co-occurred in the fish present in Zone-3. The toxin profiles may have reflected the variation in Gambierdiscus spp.

Temporal changes in the in situ germination flux of cysts and the abundance of vegetative cells of the toxic dinoflagellate Alexandrium catenella were investigated in Ago Bay, central Japan from July 2003 to December 2004. The in situ germination flux (cells m⁻² day⁻¹) was measured using ‘plankton emergence trap/chambers (PET chambers)’. Germination of the cysts in the sediments occurred continuously during the study, ranging from 52 to 1753 cells m⁻² day⁻¹, with no temporal trend. This germination pattern appeared to be promoted by a short mandatory dormancy period for newly formed cysts coupled with a broad temperature window for germination. For the vegetative populations, high abundances (>10⁵ cells m⁻²) were recorded in the water column from spring to summer and from autumn to early winter. The size of the vegetative populations did not correlate with the cyst germination flux but rather larger vegetative populations were often observed when the water temperature was around 20°C, indicating that bloom development was mainly regulated by the temperature. Nonetheless, the continuous germination pattern of A. catenella is advantageous enabling the germinated cells to immediately exploit favorable bloom conditions.

シガテラの主要毒素は，底生性渦鞭毛藻 Gambierdiscus 属が生成すると考えられている。シガテラが散発する本州太平洋岸においては，有毒種 Gambierdiscus toxicus の出現が 1980 年代から確認されている。一方，日本海沿岸ではシガテラの発生報告がなく，Gambierdiscus 属の生息も報告されていない。本研究では 2009 年 9 月に若狭湾西部の 6 定点で調査を行い，Gambierdiscus 属が日本海沿岸においても生息していることを見出した。今後は日本海産 Gambierdiscus 属の詳細な分類や広域的な分布を含め，その毒性や高次捕食魚類の毒化状況など包括的な研究の必要性が示唆される。