It’s a small fish, only a couple of inches long, and its bright colors make it pop in the Pacific coral reefs it calls home. The first thing that makes this fish peculiar is the striking pair of large lower canines it sports.
But when attacked by a predator, this fish, part of a group called fang blennies, does something even more strange. A predator that puts this fang blenny in its mouth would experience a “violent quivering of the head,” according to George Losey, a zoologist who observed this species up close in a series of feeding experiments in the 1970s. Then the predator would open its jaws and gills. The little blenny would swim away, unscathed.
“This is one of the most in-depth studies of how venom functions in any particular group of fish,” said Matthew Davis, an assistant professor of biology at St. Cloud State University in Minnesota, who did not participate in the research.
The authors of the study took a multipronged approach to studying venomous fang blennies. First, they imaged the jaws of fang blennies collected from around the Pacific and Indian Oceans to confirm what scientists long suspected: Not all fang blennies have venom glands at the base of their teeth.
Out of 100 fang blenny species, only about 30 are venomous, said Nicholas Casewell, a lecturer at the Liverpool School of Tropical Medicine and an author of the study. This pattern suggests that fang blennies first evolved large teeth, which certain species then coupled with venom.
Analyzing venom extracted from one fang blenny species, the scientists identified three toxins: an enzyme, a molecule used in neuron signaling and an opioid, in the same class as heroin and some prescription painkillers.