Every winter, the northern European crucian carp gets frozen into the ice, and receives no oxygen. Every spring, when the ice melts, a seeming miracle occurs: the fish emerges from the ice and resumes normal life.
Or, not quite. When they thaw from their winter freeze, the crucian carp's brain is not quite the same, according to new research. But the same researchers also found that the fish can recover from its months of anoxia.
The mechanism whereby the fish stays alive has been relatively well studied. It relies on glycogen stored in the body, producing ethanol via glycolysis. Their hearts can remain active without requiring oxygen output, maintaining bloodflow, and releasing ethanol over the gills to avoid intoxication.
What happens to their brains has been a little more elusive.
To test how the fish's brain responds to frozen winters, a team of researchers from the University of Oslo and the University of West Scotland caught crucian carp from a pond near Oslo and subjected them to an artificial winter in a lab.
First, the fish were deprived of oxygen - a condition normally experienced in winter when the fish are frozen. After a week, they were resupplied with oxygen for an artificial spring.
Stains were used to detect cell death and growth.
Interestingly, a lack of oxygen showed no change in the normal rate of cell death in the brain. It wasn't until the fish was reoxygenated that cell death was observed - the rate more than doubling. This is consistent with earlier research conducted by one of the researchers.
"When the anoxic fish were given 1 day of reoxygenation at normal oxygen levels, a 170 percent increase in the number of apoptotic cells was detected," wrote researcher Lisa Yuen in her 2010 Master thesis.