Humans and most other animals cannot survive long without oxygen.
We all know that breathing oxygen in frozen waters is almost improbable but goldfish seem to just slow down a bit and are not too bothered by a low-oxygen environment even in long periods. Instead of producing lethal levels of lactic acid like a human body would, the fish are equipped with enzymes that allow them to produce ethanol, which they then release. This is an issue that many fish must deal with, typically by slowing down their movement dramatically and continuing to pull oxygen out of the water by passing it over their gills, but carp have developed a particularly robust backup system for dealing with oxygen depletion. When that oxygen runs out, the cells turn to a different process, anaerobic respiration, that produces lactic acid, which can quickly build up and cause harm. If goldfish can not get rid of this lactic acid, they would die within few minutes.
The team has shown that muscles of goldfish and crucian carp contain not just the usual one, but two sets of the proteins normally used to channel carbohydrates towards their breakdown within a cell's mitochondria - a key step for energy production.
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.
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. Researches suggest that common ancestor of goldfish and crucian carp adapted to extremely cold conditions some 8 million years ago.
Most animals, including humans, require oxygen as part of the metabolic process.
"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 milligrams per 100 millilitres, which is above the drink drive limit in these countries", University of Liverpool evolutionary physiologist Michael Berenbrink said.
This metabolic adaptation gave goldfish an advantage over other fish in the water that would normally kill without oxygen.
"It's no wonder then that the crucian carp's cousin the goldfish is arguably one of the most resilient pets under human care", Fagernes said.