Think about a venomous fang, and you’ll probably conjure up an image of a snake or spider. But perhaps you should also spare a thought for group of unassuming reef fish that are appropriately called fangblennies. They are finger-sized, colorful, and rather cute—that is, until they open their mouths. Their lower jaws bear two upsettingly large canine teeth, capable of delivering a deep bite. And the evolution of those teeth, according to a new study by Nicholas Casewell at the Liverpool School of Tropical Medicine, took the fangblennies down a path of subterfuge, double-crossing, and chemical warfare.
Of the 33,000 or so species of fish, some 2,500 are venomous—far more than the number of venomous snakes. A surprising number of deep-sea sharks (including many that glow-in-the dark) have venomous spines at the base on their fins. Stingrays deliver venom with their ostentatious tail spikes, stonefish inject toxins with spines on their backs, lionfish use their flamboyant fins, and tangs deploy scalpel-like spines at the base of their tails. (So, yes, Dory is venomous.) But among this toxic underwater menagerie, only two groups have venomous bites—an obscure group of deep-sea eels, and the fangblennies.
Unlike snakes, spiders, and scorpions, the venomous blennies don’t use their poisons to hunt. “They’re mostly plankton-feeders,” says Casewell. Instead, their toxins are defensive. George Losey from the University of Hawaii demonstrated this in the 1970s by offering captive fangblennies to groupers. If the large predators swallowed the tiny fish, they would soon re-open their mouths and allow the morsels to swim out unharmed. But if Losey defanged the blennies first, the groupers readily devoured them.