Low oxygen levels in extremely cold waters make it difficult for any kind of creature to breathe. But goldfish and crucian carps – kinds of Carassius fish – have a unique way of coping.
Researchers have found that the key to goldfish’ survival in freezing waters is because their bodies get them drunk, Tech Times reports. Their cells produce alcohol in their cells by diffusing lactic acid buildup so that they can keep breathing. In short, these fish have evolved to become experts at alcohol brewing throughout time.
In order to determine how Carassius fish are able to do this, researchers grouped crucian carps and shut them in airless tanks for a week. Then they took DNA samples and sequenced these to examine how the cells worked.
It turned out that the fish have two sets of proteins in their cells that break down carbohydrates. One set functions to produce energy, while the other set comes into play when there is a lack of or absence of oxygen.
Goldfish produce an enzyme called pyruvate decarboxylase, which is similar to brewer’s yeast, the researchers said. This enzyme is released when oxygen runs low and lactic acid begins building up, and ensures that the goldfish only create ethanol through fermentation, instead of lactic acid. Too much lactic acid is dangerous for the fish.
The fish can then safely diffuse the alcohol through their gills, allowing them to survive for long periods of time even without oxygen. When the process happens, the fish barely move, also saving energy. Scientists are unsure whether or not this is because of the alcohol or because the fish just need to conserve energy.
The alcohol level in goldfish during this process is illegal in some countries. Michael Berenbrink of the University of Liverpool 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 milligrams per 100 millilitres, which is above the drink drive limit in these countries.
Cathrine Elisabeth Fagerne of the University of Oslo and lead author on the study said, “This research emphasizes the role of whole genome duplications in the evolution of biological novelty and the adaptation of species to previously inhospitable environments.”
The study was published in Scientific Reports.