It turns out that goldfish can make their own alcohol when the conditions allow for it. If that was not weird enough, researchers have now figured out how they manage their Biblical trick – it turns out they actually share the mechanism with brewer’s yeast.
The ability to turn the water they are swimming in into alcohol is actually an evolutionary adaptation to the environment in which the goldfish, as well as their close relative the crucian carp, live. During the long winter months in northern Europe, the crucian carp has to survive in ponds that frequently freeze over for extended periods of time. This prevents oxygen exchange between the water surface and the air, and so the oxygen concentrations in the water crash.
To cope with living in completely oxygen-free water, the carp astonishingly switch to anaerobic respiration for weeks on end. As they respire anaerobically, the level of lactic acid in their bodies builds up. To deal with this, they convert it into ethanol – or alcohol – before it diffuses across their gills into the surrounding water.
“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 milliliters, which is above the drink drive limit in these countries,” explains the University of Liverpool’s Dr Michael Berenbrink, co-author of the study published in Scientific Reports, in a statement. “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.”
The researchers managed to pinpoint how the fish actually achieve this impressive feat. It turns out that they produce an enzyme known as pyruvate decarboxylase, analogous to the one found in brewer’s yeast. This, in addition to a specialized alcohol dehydrogenase, is the first of this enzyme to have been found in vertebrates.
While most vertebrates have one set of proteins that are used to channel carbohydrates, like glucose, towards their breakdown within the mitochondria, crucian carp and goldfish have two. This second, duplicated protein turns out to be strongly activated in the absence of oxygen, and channels the lactic acid produced during the anaerobic respiration into ethanol outside of the mitochondria.
An analysis of both the goldfish and the crucian carps' DNA found that their ability to create alcohol evolved around 8 million years ago in a common ancestor to both the fish, during what is known as a whole genome duplication event.
Drinking like a fish has taken on a whole new meaning.