Heroin-like Venom From This Fanged Fish Could Bring New Painkillers

A timid tropical fish's numbing bite may spur the creation of tomorrow's pain treatments, but its coral reef habitats are under threat.

Fang blennies are timid and colorful fish that are popular with aquarium enthusiasts, but many of them have a venomous bite. Even skilled researchers have had their hands chomped on by venomous fang blennies, resulting in inflammation and an odd feeling that goes away after a short while.

Avoiding such problems, a scientific team recently studied fang blennies, focusing on the fish's venom. They determined that the venom is full of opioid compounds known as peptides that act like heroin or morphine, inhibiting pain rather than causing it.

"These opioid peptides are a rich source of novel leads for new painkillers," project co-leader Bryan Fry of the University of Queensland told Seeker. "This discovery is an excellent example as to why we must urgently protect all of nature. It is impossible to predict where the next wonder drug will come from.”

Venomous fang blennies are only about two inches long, but they have two large grooved canine teeth that jut out of their lower jaw. These are their secret weapons, Fry said, since these fangs are linked to venom glands.

For the study, published in the journal Current Biology, Fry, co-leader Nicholas Casewell of the Liverpool School of Tropical Medicine, and their colleagues analyzed the venom to determine its components. Three of these were of particular interest: a neuropeptide (compound that acts on the nervous system) that also occurs in cone snail venom; an enzyme similar to one found in scorpion venom; and opioid peptides like those in heroin, methadone, and related drugs.

When the researchers injected the blenny venom into mice, the rodents did not show any signs of pain.

"The key here, as one of my co-authors Irina Vetter explained to me, is that opioids act as painkillers in the central nervous system, but outside this system they cause blood pressure drops," Casewell informed Seeker. "So the fang blenny toxins are almost certainly acting to rapidly drop blood pressure, rather than inhibit pain, in their predators."

The end result is that the perceived predator, when bitten by a venomous blenny, experiences a sudden zonked-out loss of coordination. Fish victims move slowly and erratically, but live to tell the tale.

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"Notably, these peptides only have a transient effect, in that they wear off quickly," Casewell explained. "So they provide enough time for the blenny to escape, but they don't kill the predator. This allows predators to learn to avoid future encounters."

Fry said he and his team were surprised that the venom acts in this manner. Usually defensive substances produced by fish and other animals really hurt victims.

"Fish with venomous dorsal spines produce immediate and blinding pain," Fry said in a statement. "The most pain I've ever been in, other than the time I broke my back, was from a stingray envenomation. 'Stingray' sounds so benign. They don't sting. They are pure hell."

Although the venomous fang blenny's bite lacks such a painful punch, people who keep these fish in aquariums must take care to house them with other species that are compatible, such as dwarf and large angelfish, cardinalfish, clownfish, damselfish, gobies, hawkfish, and tangs.

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Larger fish that prey on the blenny perhaps led to the evolution of its fangs. This happened before fang blennys evolved their venom, which is rare, Casewell said. He explained that in snakes and other venomous animals, rudimentary venom secretions evolved before the elaborate venom delivery mechanisms emerged.

Not all blennies are venomous. Some have evolved coloration and swimming behaviors similar to the venomous species. A few "faux" fang blennies use their mimicry to great advantage, getting right up into the faces of very large potential predator fish and feeding on their scales without any repercussions.

Casewell, Fry, and their colleagues hope to study fang blennies and the venom more in future, but time is of the essence. In the wild, these coral reef fish are found in Australia's highly threatened Great Barrier Reef and other tropical waters.

"The Great Barrier Reef is currently dying due to the effects of climate change, and the Australian government has been shockingly inactive in responding to this threat," Fry said. "Instead, it has just approved the largest coal mine in Australia's history, an action that will contribute to further climate change, and thus further threaten biodiversity-based medical research."

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