We all know that breathing oxygen in frozen waters is nearly improbable but goldfish seem to just slow down a bit and are not too bothered by a low-oxygen environment even in long periods. Carassius fish, such as the goldfish and crucian carps, produce alcohol in their cells in order to ensure their survival.

Now researchers have discovered how goldfish have managed to avoid death by diffusing dangerous lactic acid buildup as alcohol. Apparently, our fishy friends have become expert alcohol brewers through the process of evolution.

In order to determine just how the Carassius fish does this, the researchers grouped crucian carps and placed them in airless tanks for about a week. Then they took DNA samples and sequenced them to determine what is going on in their cells.

What researchers discovered is that the fish actually have two sets of proteins in their cells that are responsible for the breakdown of carbohydrates. They also found that, while one set functions similarly for energy production, the other set is strongly triggered by the lack or absence of oxygen.

Legally Drunk Swimmers

According to the researchers, goldfish produce pyruvate decarboxylase — an enzyme similar to brewer's yeast — when oxygen runs out and lactic acid begins to build up. This enzyme basically ensures that goldfish will only release ethanol through the process of fermentation instead of the more dangerous lactic acid.

The Carassius fish will then be able to safely diffuse the alcohol through their gills and allow them to survive for months even without oxygen. However, since the fish tend to save energy by barely moving while the process occurs, researchers are not sure whether they are affected by alcohol or it's just a matter of energy conservation.

If it is any consolation, however, the researchers say that goldfish blood alcohol levels during this time are illegal in some countries.

"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.

But Wait ... Doesn't Brewer's Yeast Come From Plants?

The quick answer is that, yes, brewer's yeast does come from plants but goldfish have somehow managed to produce a similar enzyme.

It is highly possible that Carassius fish genes have mutated over time.

"This research emphasizes the role of whole genome duplications in the evolution of biological novelty and the adaptation of species to previously inhospitable environments," University of Oslo researcher and lead author Cathrine Elisabeth Fagerne said.

The research team hopes that other researchers would study and compare other species to determine whether there are differences in the process of alcohol production.

The study has been published in Scientific Reports.

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