BBC reports that while humans and most vertebrates die in a few minutes without oxygen, these fish are able to survive for months in icy conditions in ponds and lakes in northern Europe. 

Researchers have now uncovered the molecular mechanism behind this ability. In most animals there is a single set of proteins that channel carbohydrates towards the mitochondria, which are the power packs of cells. 

In the absence of oxygen, the consumption of carbohydrates generates lactic acid, which the goldfish can't get rid of and which kills them in minutes. 

Luckily, these fish have evolved a second set of proteins that take over in the absence of oxygen and convert the lactic acid to alcohol, which can then be dispersed through the gills. 

Scientists have also calculated for fun, how long it would take to produce an alcoholic drink from the fish excretions. Should you put them in a beer glass and closed them off, it would take 200 days to get it up to 4%. But in nature, it just would not happen.

BBC