A total of 256 specimens of “Nashifugu” pufferfish Fugu vermicularis vermicularis were caught in Ariake Bay from June 1993 to May 1994, and examined for anatomical distribution of toxin by the standard mouse assay method for tetrodotoxin. The frequency of the specimens whose toxicity exceeded the quarantine limit (10MU/g) was 84% for skin, 72% for liver and 100% for ovary. The highest toxicity scores were 3120MU/g in skin, 2910MU/g in liver and 6240MU/g in ovary. In regard to muscle, only 4 specimens caused death with toxic symptoms in mice and their toxicities were calculated to be <5-7MU/g. However, they did not show any toxicity when tested on the deep part of the muscle. In further experiments, the surface part of skinned bodies of “Nashifugu” pufferfish was mostly toxic, though the deep part of the muscle did not show any toxicity. It was also shown that the surface part washed with water was nontoxic. Thus, the toxic result on the muscle was considered to be due to the contamination of tetrodotoxin from toxic skin during preparation of the samples.
