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Fang Blennies: The Aquarium Fish With Heroin-Like Venom

The Heroin Fish: Fang Blennies

Fang blennies are kept in tropical aquariums all over the world. The fish look cute and harmless, but they hide a terrifying ability. When a predator grabs it, a blenny bites like a snake and injects poison into the attacker. But unlike most other fish toxins, the venom causes no pain.

The bite isn’t useless, however. A dose of blenny revenge is full of opioid hormones that act like heroin or morphine. Apart from getting the predator high, the toxin also crashes its blood pressure.

A hunting scene involving a blenny would go something like this. The predator thinks the blenny is an easy lunch. But once inside the cavernous mouth, the blenny strikes. The poison acts fast and the larger fish, now feeling faint or trippy, slackens its jaw, allowing the blenny to escape.

Blennies sometimes use their venom on their own kind but not in self-defence. When a territorial fish falls in love with a patch of coral, it will bite a rival that also wants to move in (or an unlucky blenny that already lives there might get evicted). Luckily for the guy who lost the real estate battle, the effects of the toxin wear off in a few hours.

The striped blenny

The striped blenny

The Unique Venom

Did you also know that blenny bites are giving the scientific world goosebumps?

Researchers love finding things for the first time and this venom is unique. Indeed, the heroin-like chemicals and painless aftermath have never been seen before in any toxin from venomous fish, reptiles or plants.

The reason why researchers are excited by the discovery, which was made in 2017, is the fact that the venom could create new painkillers for humans. You know, without getting them high and all that!

Non-Venomous Blennies Fake It

Predator fish aren’t stupid. By either accident or experience, they eventually learn how to recognize a toxic fang blenny. The latter has certain patterns and swimming behaviours. However, not all blennies are poisonous. Incredibly, to avoid being eaten by predators, several species of non-toxic blennies have evolved to look and swim exactly like the venomous type.

How Many Blennies Are Poisonous?

There are about 100 species but only 30 types of blennies are not to be trifled with! There could be more than 30 toxic species but for now, that seems to be the rough number that experts agree upon.

The beautiful Australian blenny

The beautiful Australian blenny

A Surprising Twist

When scientists analyzed the genetic history of fang blennies, they were blown away by a bizarre step in their evolution.

Blennies are known for their large fangs (which are hidden inside their mouths). Apparently, all blennies developed their vicious teeth long before one group grew venom glands. Only then did the poisonous fish develop the grooves inside their fangs that allow them to inject the poison into an enemy or rival. It remains unknown why a tiny fish would evolve large fangs when, without venom, the teeth are essentially useless.

Well, yes. Some blennies do have a nasty bite but it does not seem to have any effect on humans. In the 1970s, when scientists first became aware of the unusual venom, a zoologist named George Losey allowed blennies to bite him on the hand and hip. He did not get high (let’s hope that was not his main intention!).

Fang blennies are popular aquarium fish. They are colourful and inquisitive. They are relatively easy to keep and care for. Blennies also adapt well to smaller tanks. For those who like to breed fish, fang blennies are also a good choice because they readily reproduce when the conditions are right.

The diamond blenny.

The diamond blenny.

Fascinating Creatures

A good rule is to never underestimate coral fish, and fang blennies are a prime example. These cute and tiny fish have fangs that deliver a heroin-like venom capable of incapacitating attackers for several hours. Or another blenny who wants the same coral tree!

The unique venom oddly evolved after their large fangs, and it might offer humanity exciting new painkillers in the future. Since a bite from a blenny cannot harm a person, there is no law against keeping these fish.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Jana Louise Smit


Peggy Woods from Houston, Texas on May 30, 2021:

It would be wonderful if scientists can turn the venom from these blennies into a useful pain killer for humans. Thanks for writing about these fascinating sea creatures.

Jana Louise Smit (author) from South Africa on May 30, 2021:

Thanks, Linda. I'm really happy your enjoyed it!

Linda Chechar from Arizona on May 30, 2021:

The scientists have a way to use the venom as a useful painkiller. These are thanks for the article, Jana!

Jana Louise Smit (author) from South Africa on May 30, 2021:

Hi Bill. I was unaware of blennies too until I recently read about them in science journals. That took me down a fascinating path of discovery and research! I just had to throw a hub out there about blennies and their strange venom. :)

Bill De Giulio from Massachusetts on May 30, 2021:

What a fascinating fish that I wasn’t aware of. I’m always amazed at the unique creatures that have evolved in the oceans of the world. Hopefully scientists can find a way to use the blenny venom as a useful painkiller. Great hub, thanks for the education, Jana.