Fish that snoozes for years with no food and water

The African lungfish can sleep out of water for three to five years without any sustenance, only to wake up when freshwater surroundings become available.

A study showing what happens on the cellular level to the fish could help scientists one day induce a similar state in humans, making long distance space travel and more advanced forms of medicine possible.

During suspended animation, the fish don't eat or drink and produce no waste, sometimes for as long as five years.

The researchers claim that in the process they slow down their biological clock, relinquishing the normal need for sustenance and surviving in a very low energy state. 

This kind of suspended animation has always fascinated scientists because if it could be replicated in some form in humans.

It could be induced in patients in critical conditions - such as gunshot wounds - in order to buy some extra time to operate without the brain shutting down.

It would also allow astronauts to go into hibernation during long distance space missions.

Scientists at the National University of Singapore discovered that entering and maintaining this state, known as aestivation, involves the regulation of diverse cellular activities.

“Overall, our results signify the importance of sustaining a low rate of waste production and conservation of energy store during the maintenance phase, and the dependence on internal energy store for repair and structural modification during the arousal phase, of aestivation in the liver,” wrote the researchers in their paper.

Researchers led by Professor Ip Yuen Kwong from the biological sciences department compared the differential gene expression in the liver of African lungfish after six months of suspended animation to fish in a normal state in freshwater.

They also compared the gene expression from the first day of arousal after suspended animation - when the fish wake up - to gene expression during the hibernation phase.

During suspended animation, genes related to detoxifying waste were “up-regulated”, stopping the build-up of harmful products in the liver.

Simultaneously, the expression of genes related to blood coagulation and iron and copper metabolism were “down-regulated”, which the researchers say could be strategies to conserve energy. The results were published in the journal Plos One.

The African lungfish is one of the closest relatives of tetrapods, the first group of four-limbed vertebrates to live outside of water.

Their anatomy offers clues as to how animals first evolved to breathe air, as they have adapted a lung that can sustain them in periods when their environment dries up.

In addition to being able to gulp air to breathe, they are able to pump oxygenated blood separately to deoxygenated blood, similar to mammals.

They pass the long stretches of the dry season holed up in burrows in the mud, and they can use their long appendages to crawl and move outside of the water.