Geographical differences in the composition of tetrodotoxin and 5,6,11-trideoxytetrodotoxin in Japanese pufferfishes and their origins.

Tetrodotoxin (TTX)-bearing fish are thought to accumulate TTXs in their bodies through a food chain that begins with marine bacteria. However, the mechanism of TTXs transfer between prey and predators in the food chain remains unclear and the reasons for regional differences in pufferfish toxicity are also unknown. To investigate these matters, we collected juveniles of four species of pufferfish, Takifugu alboplumbeus, Takifugu flavipterus, Takifugu stictonotus, and Chelonodon patoca, from various locations in the Japanese Islands, and subjected them to liquid chromatography-tandem mass spectrometry analysis for TTX and its analog 5,6,11-trideoxyTTX (TDT). Concentrations of these substances tended to be higher in pufferfish juveniles collected from the Sanriku coastal area (Pacific coast of northern Japan) than in those from other locations. Juveniles had higher concentrations of TTX at all locations than of TDT. Mitochondrial cytochrome c oxidase subunit I (COI) sequences specific to the TTX-bearing flatworm, Planocera multitentaculata, were detected in the intestinal contents of up to 100% of pufferfish juveniles from various sampling sites, suggesting that P. multitentaculata was widely involved in the toxification of the juveniles in the coastal waters of Japan. A toxification experiment was conducted on three species of pufferfish juveniles (T. alboplumbeus, Takifugu rubripes and C. patoca) using TTX-bearing flatworm eggs harboring equal amounts of TTX and TDT. The TTX content of juveniles fed on flatworm eggs was found to be more than twice that of TDT, suggesting that pufferfish preferentially incorporate TTX compared to TDT.