To escape its predators, this little fish has a weapon of choice: it shoots them!

Scientists have discovered a unique chemical venom in meiacanthus atrodorsalis, a small tropical fish. Unlike most venomous creatures, this fish does not use its venom to capture its prey, but to escape its predators by « shooting » them.

Meiacanthus atrodorsalis is a species of saltwater fish in the family Blenniidae that is found on reefs in the western Pacific. Measuring only four inches, they are popular in aquariums, yet harbor a fascinating evolutionary secret. In nature, unlike aquariums, meiacanthus atrodorsalis is constantly under threat from predators. To defend itself, this small fish has a weapon of choice: fangs located on the lower jaw which deliver a particular venom: a chemical cocktail loaded with opioid peptides, which are found in particular in morphine, or heroin .

There are at least 2,500 poisonous fish in nature, most delivering venom through spines on their fins, tails, or backs. They have at least the common point of inflicting excruciating pain through their mixtures on their prey or adversaries. But the venom of meiacanthus atrodorsalis is totally different. Our little tropical fish is thus part of the very closed club of two species of fish (the other is an eel) which inject venom by biting, as a snake would do. And not only does its venom inflict no pain – but it also contains opioid hormones that act as painkillers.

 » Its venom is chemically unique. This fish injects other fish with venom filled with opioid peptides that act like heroin or morphine, inhibiting pain rather than causing it“, explains Brian Fry, from the University of Queensland in Australia, and lead author of this study published in the journal Current Biology.

CT scan of a venomous fang blenny/Anthony Romilio

On the other hand, this venom would not act as morphine or heroin could do in humans once released in the brain. Instead, researchers believe the venom blocks the predator’s blood pressure, making it weak and dizzy, causing it to loosen its grip and let its prey escape.

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