Assay of toxicity
The test solution for toxicity assay was extracted from
the viscera of the crabs, and from the whole edible part of
other specimens. Briefly, each tissue was ground with the
same volume of 0.1N HCl, and heated in boiling water for
5 min after adjusting the pH to 2–4. The mixture was
centrifuged, and the supernatant was examined by the
mouse bioassay method which is the official Japanese
method for PSP monitoring (Kawabata, 1978). The activity
was expressed in mouse units (MU), 1 MU being defined as
the amount of toxin required to kill a 20 g ddY strain male
mouse in 15 min after intraperitoneal injection.