Goldfish make their own alcohol in bid to survive extreme conditions

11 Aug 2017

Image: Mirek Kijewski/Shutterstock

New research into a goldfish’s ability to withstand extreme conditions has found it turns to alcohol in a bid to survive.

How a goldfish manages to tolerate the extreme, oxygen-depleted environments of frozen lakes for up to months at a time has often puzzled biologists, but new research has found that it’s down to some locally brewed alcohol.

In a paper published to Scientific Reports, a team of researchers from the University of Liverpool discovered that goldfish and their wild relatives, the crucian carp, are able to convert anaerobically produced lactic acid into ethanol.

This diffuses across their gills into the surrounding water, helping to prevent a dangerous build-up of lactic acid in the body, making it unique among vertebrates.

Possibly dating back to a mutation 8m years ago, the process was found in the muscles of goldfish and crucian carp, which contain two sets of the proteins normally used to channel carbohydrates towards their breakdown for energy production in a cell’s mitochondria.

While one of the proteins is similar to its vertebrate cousins, the second has been found to switch on in the absence of oxygen, allowing for the production of alcohol outside the mitochondria.

Enough to put a human over the limit

How much alcohol is produced might astound some, with crucian carp creating up to 50mg of alcohol per 100ml of blood, above the drink-driving limit of many countries.

“This is still a much better situation than filling up with lactic acid, which is the metabolic end product for other vertebrates, including humans, when devoid of oxygen,” said Dr Michael Berenbrink, an evolutionary physiologist at the University of Liverpool.

In trying to explain the possibly evolutionary purpose of the unique trait, lead author of the paper Dr Cathrine Elisabeth Fagernes said: “The ethanol production allows the crucian carp to be the only fish species surviving and exploiting these harsh environments, thereby avoiding competition and escaping predation by other fish species with which they normally interact in better-oxygenated waters.

“It’s no wonder then that the crucian carp’s cousin, the goldfish, is arguably one of the most resilient pets under human care.”

Colm Gorey was a senior journalist with Silicon Republic