Tetrodotoxin in Asian horseshoe crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus across different life stages from northern Beibu Gulf, China.

Horseshoe crabs (HSCs) are a group of ancient chelicerates with great ecological and biomedical importance. Food poisonings caused by the consumption of Asian HSCs have significant impacts on public health and safety. This study measured tetrodotoxin (TTX) concentrations in two HSC species across various life stages in May 2020 from the northern Beibu Gulf, their most important spawning and nursery habitats in China. The average TTX contents in both Carcinoscorpius rotundicauda and Tachypleus tridentatus ranged 6.2-8.0 µg/kg and 3.8-8.4 µg/kg, respectively. While sampling location, growth and molt stages have little influence on TTX distribution in both species, significantly higher levels of TTX were detected in hemolymph, but lower in pooled tissues of early-instar juvenile T. tridentatus. These results provide a regional view of TTX occurrence and distribution in HSCs during their spawning season, which are critical for future studies to enhance understanding of TTX dynamics and formation in HSCs.