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Most animals have a way to protect themselves from predators. The antelope is fast because its predilection is to run, the tortoise has a shell to hide behind in case a predator comes hunting. The scorpion and the snake are known for their poisonous venom that keeps any hunters at bay, and now, a tiny tropical fish has been discovered to have venom to protect itself.

The tropical fish under discussion is known as the Meiacanthus atrodorsalis or the fanged blenny. It is a small fish, only inches long, found mainly in the Pacific and Indian Oceans. The fanged blenny is getting ecologists excited because it has many unusual characteristics that are changing the way researchers look at marine life.

The Unique Little Fish

The first time this fish came under scrutiny was in the 1970s when George Losey, a zoologist, studied them in his home. Losey put the fanged blennies in a tank filled with groupers. Over time he observed that the fanged blenny would get swallowed by the groupers because it is a small prey. However, Losey could not understand why a short while later the blenny would swim out of its captors’ mouth, unharmed.

To test out his hypothesis, Losey defanged some blennies and again fed them to the groupers. He realized that the larger fish had no problem consuming the blennies after that. Losey then concluded that the blennies’ relatively large lower canines must have had something to do with why the fish was rarely hunted.

Decades later, an international group of scientists has solved the mystery of the fanged blenny. In a paper published in the Current Biology journal, Dr. Nicholas Casewell of the University of Liverpool’s School of Tropical Medicine explains the defense mechanism of the fanged blenny.

For their study, Casewell and his partners Bryan Fry and Irine Vetter gathered samples of the fanged blennies. The team discovered after several tests that only about a third of the sample blennies were venomous. Casewell explained that this must have been an evolutionary mechanism depending on what part of the sea the blenny was situated in.

Another observation the team made was that the venomous fanged blenny’s mode of transmission of its venom was unique. Typically, venomous land animals are the ones that inject venom via bites while fish inject it using their fins, tails, and backs. The fanged blenny, however, used its lower canines to inject its venom into its attacker. The only other sea creature that shares this characteristic is a bizarre eel that scientists are yet to understand.

The researchers also unveiled the fact that the fish’s venom was comprised of unusual ingredients- an enzyme that causes inflammation, a neurotoxin that drops blood pressure and opioid, the kind found in heroin and some painkillers. By testing out the venom on mice, Casewell and his team discovered that the venom of the fanged blenny dropped the rats’ blood pressure by up to forty percent, making them uncoordinated and slack. The group proposed that that is why predators often ‘let go’ of the venomous fish. Fry also noted that unlike other toxic transmissions, the fanged blenny’s bite is not painful and Vetter clarified that this was unrelated to the venom containing opioid.

One other interesting fact that the team reported is that other fish mimicked the venomous fanged blenny in color, swimming style, and patterns to avoid predation.  Call it the survival instinct.