Alcohol brewing goldfish

Scientists have discovered that goldfish survive harsh winters beneath frozen lakes by producing alcohol in low oxygen environments.

Most vertebrate animals and humans die within a few minutes without oxygen. Goldfish and their wild relatives – crucian carp – can survive for months at a time at the bottom of ice covered ponds. This is achieved by fish converting anaerobically produced lactic acid into ethanol which diffuses across their gills into surrounding waters. They can survive for up to five months underwater, relying on glycogen stored in their liver.

Above the limit

Dr Michael Berenbrink, from the University of Liverpool and co-author of the study, said: “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 50 mg per 100 millilitres, which is above the drink drive limit in these countries.”

The researchers discovered that crucian carp and goldfish muscles contain, unusually, two sets of the protein used to channel carbohydrates towards their breakdown within the mitochondria. Although one set appears similar to that in other species, the second is strongly activated by oxygen absence. It has a mutation enabling metabolic substrates to be converted to ethanol outside the mitochondria.

Dr Catherine Fagernes, from the University of Oslo and lead author, said: “This research emphasises the role of whole genome duplications in the evolution of biological novelty and the adaptation of species to previously inhospitable environments.

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.”

The research was published in Scientific Reports.