Tissue distribution of diarrhetic shellfish toxins in ascidian Halocynthia roretzi

Ascidian Halocynthia roretzi is a very important aquacultured species on the coast of Miyagi Prefecture. In Miyagi Prefecture, the harvest season of this species is from late spring to early summer, which is also the season when Dinophysis species as the causative plankton of diarrhetic shellfish poisoning (DSP) have been observed in the coastal waters. There have been reports on the detection and tissue distribution of diarrhetic shellfish toxins (DST) in H. roretzi, but there are few reports on such tissue distribution throughout the DSP season. In this study, we detected DST toxins from H. roretzi throughout the DSP season and compared them with the mussel Mytilus galloprovincialis, an indicator species of DST. The results indicated that almost all of the DST were contained in the hepatopancreas of H. roretzi throughout the DSP season, and that H. roretzi was poisoned by D. fortii as well as M. galloprovincialis. Among the results, okadaic acid (OA) was detected in H. roretzi as well as dinophysistoxin 1 (DTX1). On the other hand, no OA was detected in M. galloprovincialis in this study or previous studies in Miyagi Prefecture. These findings suggest that there might be different metabolisms of DST between distinct taxa.