These brightly coloured blennies are a popular choice for home aquariums, but it turns out they harbour a fascinating evolutionary secret in their (relatively) giant fangs.
Instead, the researchers think the venom crashes the predator's blood pressure, making them faint and dizzy, which loosens their grip and lets the blenny escape.
A fearless fanged coral reef fish that disables its opponents with heroin-like venom could offer hope for the development of new painkillers. A new study shows their venom doesn't inflict pain when tested in mice, unlike the often-excruciating stings of other poisonous fish. When injected with the venom, mice showed blood pressure drops of almost 40 percent-but didn't show significant signs of distress.
An analysis of the venom found three key components - a neuropeptide also found in cone snail venom, a lipase found in scorpions, and an opioid peptide. "Fish with venomous dorsal spines produce immediate and blinding pain. They would be more likely to drown than win gold", he said.
"The predators would shake and quiver, and open their jaws and gills really wide", says Nick Casewell of the Liverpool School of Tropical Medicine, UK, and joint leader of a team that has established the ingredients of blenny venom.
Casewell believes that all of the mimicking that takes place among those fishes is ultimately stimulated by the venom system that the fang blennies have. And one seems to be a chemical similar to opioids, including prescription painkillers like Percocet and OxyContin and street drugs like heroin, which may explain why grouper seem so out of it after a blenny bite. They make their living by nibbling on the scales and fins of bigger fish. The fish were then returned to the tanks and the swabs were suspended in a solution to draw out the venom. They discovered something pretty wild: That the fish attack predators with a venom that acts on animals' opioid receptors, the same ones activated by opium-based drugs. Although used for defence, the venom "inhibits pain rather than causing it". Fry and his colleagues determined that, unlike in venomous snakes, where venom evolved before the fangs that could deliver the weapon, fang blennies evolved fangs first and venom later. However, the researchers observed about 40 percent drop in the mice's blood pressure.
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In the study, a team of global researchers analyzed those glands and found the toxins are a chemical mix of different opioid peptides that act like morphine or heroine. The team plans to continue their research into the special toxic blend by comparing the venom of different blenny species against each other.
If you want to see evolution at its most attractive and deadly, look no further than this tiny fish that puts its predators into a drugged stupor.
The venom is "chemically unique", Fry said, which drives home the importance of biodiversity.
'While the feeling of pain is not produced, opioids can produce sensations of extremely unpleasant nausea and dizziness in mammals'.
Their behaviour is also intriguing, he said, for the way they appear unafraid of predators and fight for territory with similar-sized fish.
Prof Fry concluded: 'This study is an excellent example of why we need to protect nature.