Differential Accumulation and Excretion of Tetrodotoxin and 5,6,11-Trideoxytetrodotoxin in the Mussel Mytilus galloprovincialis Following Ingestion of Toxic Flatworm Larvae.

Tetrodotoxin (TTX), commonly known as pufferfish toxin, is widely distributed among marine organisms. In the past decade, TTX has been detected in edible bivalves along coasts worldwide, raising concerns about unexpected food poisoning. Recent research suggests that planktonic larvae of the TTX-bearing flatworm Planocera multitentaculata are involved in the toxification of bivalves. However, some uncertainties remain: although these flatworms contain large amounts of 5,6,11-trideoxytetrodotoxin (TDT), TDT is generally not detected in bivalves, even when TTX is present. The aim of this study was to characterize the accumulation and excretion of TTX and TDT in the mussel Mytilus galloprovincialis after ingestion of toxic P. multitentaculata larvae and to determine whether differences in their excretion could explain the rarity of TDT in naturally contaminated bivalves. LC-MS/MS analysis revealed that the toxified mussels accumulated both TTX and TDT in the midgut gland. However, the concentrations of both compounds decreased over time, with TDT showing a faster decline than TTX. These findings provide the first evidence for the accumulation and excretion of TDT in bivalves and suggest that its faster elimination contributes to its rare detection in naturally contaminated specimens. The results also indicate that detection of TDT in wild bivalves may reflect relatively recent ingestion of TTX-bearing organisms, providing new insights into TTX analog dynamics and contributing to seafood safety monitoring.