Scientists have figured out how goldfish produce alcohol to survive when trapped beneath the icy surfaces of frozen lakes and ponds.

Unlike most vertebrates which die within a few minutes without oxygen, goldfish and their wild relatives crucian carp are able to survive for months in oxygen-free water.

Biologically speaking, the fish convert their anaerobically produced lactic acid into ethanol which diffuses across their gills into the surrounding water.

The researchers from the Universities of Oslo and Liverpool have discovered the unusual molecular mechanism behind this unique ability.

They have pinpointed sets of proteins which are normally used to produce energy by channelling carbohydrates towards their breakdown within a cell's mitochondria.


While one set of those proteins is very similar to what other species of vertebrate possess, the second set is uniquely activated by the absence of oxygen.

Dr Michael Berenbrink, an evolutionary physiologist at the University of Liverpool, said that the blood alcohol concentration in these fish can exceed the drink-drive limit during the winter.

"During their time in oxygen-free water in ice-covered ponds, which can last for several months in their northern European habitat, blood alcohol concentrations in crucian carp can reach more than 50mg per 100 millilitres," said Dr Berenbrink.

"However, 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."

Lead author Dr Cathrine Elisabeth Fagernes, from the University of Oslo, 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."