Pufferfish are in the family Tetraodontidae with 120 species in 19 genera. Porcupinefish are in the Family Diodontidae with 22 species in 7 genera.
Pufferfish and porcupinefish are often mixed together as one group. They are scientifically in different families but have many similarities and only porcupinefish have spines. Both puffers and porcupinefish are gentle creatures that only use their defences if attacked by a predator. They have an unusual defense mechanism – expanding into an enormous ball if threatened. They deploy a special valve in their mouths to suck water into a pleated stomach, expanding up to 3 times their normal size.
These prolific reef residents also harbour a dangerous secret – they are believed to be the second–most poisonous vertebrates in the world, after the golden poison frog.
They contain one of nature's most dangerous poisons, tetrodotoxin, a naturally occurring toxin that was once assumed to be a metabolic product of the fish. Recent research now points to the production of tetrodotoxin by several relatively common bacterial species that are eaten by reef animals. Although they become immune to it, the puffers accrue the toxin in their internal organs and skin.