Occurrence of Natural Interspecific Hybrids in the Pufferfish, Genus Takifugu, and Their Tetrodotoxin-accumulating Tissues

Pufferfish in the genus Takifugu accumulate the potent neurotoxin tetrodotoxin (TTX) in specific tissues that vary by species; nevertheless, certain species are consumed as a luxury food in Japan. Therefore, the edible species and tissues of Takifugu pufferfish are regulated in Japan. In recent years, unidentifiable individuals with atypical morphological characteristics caught in waters around Japan have been found to be natural interspecific hybrids among Takifugu species. Four cases of natural hybridization have been reported; in all cases, hybrids had external characteristics intermediate between those of the parental species. Although the frequency of these hybrids was generally low, it is high in certain parental species combinations. The TTX accumulation in tissues of natural and artificial hybrids was investigated and it was inferred that TTX accumulation in the skin is dominantly inherited. However, information on hybrids’ toxicity in Takifugu pufferfish remains insufficient, and further research is required to prevent TTX poisoning associated with them.