Toxicity of cultured puffer fish and seasonal variations in China

To confirm the toxicity or the tetrodotoxin (TTX) content of cultured puffer fish in China, 565 specimens of cultured puffer fish (Takifugu rubripes, Takifugu fasciatus or Takifugu obscurus, Takifugu flavidus and Takifugu bimaculatus) were collected from five provinces from November 2007 to November 2008. The toxicity of the skin, muscle, liver and testis/ovary was examined using methods based on a mouse assay for TTX. The results indicated that the skin, muscle, liver and testis of specimens were ‘non‐toxic’ in both of the mouse assays [<10 mouse unit (MU) g^?1 or 2.2 μg g^?1] from the viewpoint of food hygiene. However, TTX was detected from an ovary sample of the cultured T. rubripes collected from the Shandong province in March 2008, which was 125.43 MU g^?1 tissue. The average TTX contents in the muscle, liver and skin of T. rubripes from Hebei and Shandong provinces were the highest in May or July (1.31, 0.90 and 0.62 MU g^?1, respectively, in Hebei, and 1.57, 0.32 and 0.16 MU g^?1, respectively, in Shandong) and the lowest in January (<0.1 MU g^?1 or 0.02 μg g^?1). Thus, non‐toxic cultured puffer fish could be produced successfully in mainland China.