Strange, non-oxygen-breathing animal poses more questions than answers

26 Feb 2020

Image: © SciePro/

Researchers have discovered a rather unique creature that doesn’t require oxygen to breathe, but aren’t sure how it generates energy.

Researchers at Tel Aviv University have published a study to the Proceedings of the National Academy of Sciences revealing a truly strange animal that doesn’t require oxygen to live.

The tiny, less than 10-celled parasite, Henneguya salminicola, lives in salmon muscle. As it evolved, the creature, which is from the same family as jellyfish and corals, ditched the need to breathe and consume oxygen to produce energy.

“Aerobic respiration was thought to be ubiquitous in animals, but now we confirmed that this is not the case,” said Prof Dorothee Huchon, who led the research.

“Our discovery shows that evolution can go in strange directions. Aerobic respiration is a major source of energy, and yet we found an animal that gave up this critical pathway.”

While organisms such as fungi and amoebas in oxygen-free (anaerobic) environments have lost the ability to breathe over time, this new study shows the same thing can happen to animals. This may be because the parasite happens to live in an anaerobic environment.

The parasite’s oxygen-free existence was discovered by accident when its genome was being sequenced, after Huchon noted it did not include a mitochondrial genome. The mitochondria is the powerhouse of the cell, where oxygen is captured to make energy.

Microscopic black and white image of the circular, non-oxygen breathing animal.

Image of H salminicola mitochondrion-related organelle with few cristae. Image: American Friends of Tel Aviv University

Impact on evolutionary science

Until this discovery, there was debate over whether organisms belonging to the animal kingdom could survive in anaerobic environments. This was assumed on the fact that animals are multicellular, highly developed organisms that first appeared when Earth’s oxygen levels rose.

“It’s not yet clear to us how the parasite generates energy,” Huchon said. “It may be drawing it from the surrounding fish cells, or it may have a different type of respiration such as oxygen-free breathing, which typically characterises anaerobic non-animal organisms.”

Whatever the outcome, Huchon added, the creature’s discovery has major implications for evolutionary research.

“It is generally thought that during evolution, organisms become more and more complex, and that simple single-celled or few-celled organisms are the ancestors of complex organisms,” she said.

“But here, right before us, is an animal whose evolutionary process is the opposite. Living in an oxygen-free environment, it has shed unnecessary genes responsible for aerobic respiration and become an even simpler organism.”

Colm Gorey was a senior journalist with Silicon Republic