Including planocerid flatworms in the diet effectively toxifies the pufferfish, Takifugu niphobles.

Beginning with the larval stages, marine pufferfish such as Takifugu niphobles contain tetrodotoxin (TTX), an extremely potent neurotoxin. Although highly concentrated TTX has been detected in adults and juveniles of these fish, the source of the toxin has remained unclear. Here we show that TTX in the flatworm Planocera multitentaculata contributes to the toxification of the pufferfish throughout the life cycle of the flatworm.

Seasonal Changes in the Tetrodotoxin Content of the Flatworm Planocera multitentaculata.

Tetrodotoxin (TTX) is a potent neurotoxin that acts specifically on voltage-gated sodium channels on excitable membranes of muscle and nerve tissues. The biosynthetic process for TTX is unclear, although marine bacteria are generally thought to be the primary producers. The marine flatworm is a known TTX-bearing organism, and is suspected to be a TTX supplier to pufferfish.