Tetrodotoxin Detection in Japanese Bivalves: Toxification Status of Scallops

Tetrodotoxin (TTX), or pufferfish toxin, has been frequently detected in edible bivalves around the world during the last decade and is problematic in food hygiene and safety. It was reported recently that highly concentrated TTX was detected in the midgut gland of the akazara scallop Chlamys (Azumapecten) farreri subsp. akazara collected in coastal areas of the northern Japanese archipelago. The toxification of the bivalve was likely to involve the larvae of the flatworm, Planocera multitentaculata. However, the overall status of bivalve TTX toxification has not been elucidated. In this study, 14 species/subspecies of bivalves from various Japanese waters were subjected to LC-MS/MS analysis to reveal TTX toxification state, demonstrating that the Pectinidae, including C. farreri akazara, Chlamys farreri nipponensis, Chlamys (Mimachlamys) nobilis, and Mizuhopecten yessoensis, accumulated TTX in their midgut gland. Many individuals of C. farreri akazara and C. farreri nipponensis were found with high concentrations of TTX, while C. nobilis and M. yessoensis exhibited low concentrations. The extent of TTX accumulation in C. farreri akazara and C. farreri nipponensis varied widely by region and season. Curiously, no other bivalve species investigated in this study showed evidence of TTX. These results suggest that monitoring for TTX, like other shellfish toxins, is necessary to ensure that pectinid bivalves are a safe food resource.