Tetrodotoxin, the chemical weapon of choice for pufferfish, is such a potent neurotoxin that a single animal contains enough poison to paralyze and kill dozens of predators, and even adult humans who dare to eat their delicate flesh. But new research suggests the poison serves another purpose for the fish entirely: stress relief.
Japanese, or tiger, puffers (Takifugu rubripes) don’t make their own tetrodotoxin (TTX), but instead accumulate it in their organs and skin from TTX-making bacteria in their diet. Those raised in captivity tend to have different diets and, thus, lose their toxicity. To find out how the toxin affects developing fish, researchers augmented the diets of young, captive puffers with a dosage of purified TTX for 1 month.
Puffers with replenished toxin stores grew a median of 6% longer and 24% heavier than those raised on a nontoxic diet. They were also less aggressive, nipping at each other’s tail fins less frequently. Growth rate and aggression are influenced by stress, so researchers also looked at levels of two stress-linked hormones: cortisol in the blood and corticotropin-releasing hormone in the brain. The nontoxic fish had higher levels of both, with a median level of cortisol four times that of the toxic fish, the researchers report online in Toxicon.
The findings suggest TTX isn’t just for keeping predators at bay, but is also essential for the healthy development of young pufferfish. Other research shows that without TTX, young puffers make riskier, potentially deadly decisions. For now, it’s unclear how, biologically, TTX blunts stress in puffers. But it’s unlikely to take the edge off daredevil diners who want to throw some pufferfish down the hatch after a stressful week.