What are blennies? Meet the predator fish who might carry the next opioid drug.

Fang blennies, a type of reef-dwelling venomous fish, are just two inches long — but they're not ones to mess with.

A new study into the small fish's venom, published in Current Biology, revealed the fish have a defensive venom with a distinctive result. Rather than inflicting pain to defend against predators, the fang blennies' venom instead contains opioid properties that, when injected into mice, caused their blood pressure to plummet by 40%, the New York Times reported. 

"The fish injects other fish with opioid peptides that act like heroin or morphine, inhibiting pain rather than causing it," said Brian Fry, a researcher and associate professor at the University of Queensland, Australia, in a statement. "Its venom is chemically unique. The venom causes the bitten fish to become slower in movement and dizzy by acting on their opioid receptors."

"To put that into human terms," Fry continued, "Opioid peptides would be the last thing an elite Olympic swimmer would use as performance-enhancing substances. They would be more likely to drown than win gold."

The fish, which are also known as poison-fang blennies or saber-tooth blennies, are often found in aquariums, according to the International Business Times.

Fang blennies typically eat plankton and algae, so the fish aren't using their fangs and venom to catch prey, study author Nicholas Casewell told Gizmodo. Rather, the opioid venom works as a protective measure to ward off predators — and, as the Sydney Morning Herald noted, claim the best coral reef real estate for themselves. 

"These fish are little jerks basically," Fry told the Herald.

These little jerks' venom, though, could hold an important key for humans. Fry told the Herald that the venom's opioid peptides are "identical to our natural painkiller ones," and the peptide's small size may mean it would be easier for scientists to create a synthetic version that humans could absorb.

The potential influence these fish hold offers an important reminder of why their habitats, such as the Great Barrier Reef, need to be preserved in the face of climate change.

"This study is an excellent example of why we need to protect nature," Fry said in the statement. "If we lose the Great Barrier Reef, we will lose animals like the fang blenny and its unique venom that could be the source of the next blockbuster pain-killing drug."