The Only Animal That Can Live Without Oxygen

Scientists have recently discovered an animal - the first of its kind to be found - that does not require oxygen in order to live. It is a parasite commonly seen inside salmon, which is its host. The study was recently published in the Proceedings of the National Academy of Sciences journal.

Henneguya salminicola is a cnidarian and a member of the family Myxozoa, a group of microscopic animals closely related to hydroids and jellyfish. The study found that it does not need  aerobic respiration for survival, which is a startling revelation that could significantly alter our perception of life on our planet and the cosmos.

Through genomic and microscopic analysis of the animal, scientists found that it lacks mitochondrial DNA. The mitochondrial genome is the small portion of the DNA found inside the mitochondria that has the genes responsible for respiration.

H. salminicola's lost its capacity to perform aerobic respiration on the cellular level. It has spent its entire life residing inside and infecting dense muscular tissues of underwater worms and fish, and thus didn't have much opportunity to utilize oxygen and convert it into energy. The DNA of all other multicellular animals that have so far been studied has respiratory genes. In contrast, the genome of H. salminicola's does not.

There have been previous discoveries of single-celled organisms that also do not respire or breathe. In 2010, another study looked into whether a loriciferan animal species, which is also microscopic, could survive in the absence of oxygen, although their findings haven't been satisfactorily confirmed.

 H. salminicola is relatively common,. It is a salmon parasite that causes "tapioca disease" or "milky flesh disease" in the fish, as stated by the Alaska Department of Fish and Game in their fishing guide. This type of disease causes unsightly cysts to form on the flesh of salmon, although it is relatively harmless even if humans consume it. It is also harmless to the salmon. H. salminicola lives inside the salmon, and since this environment has inadequate oxygen, the tiny organism has adapted by doing away with the need for oxygen for its physiological processes and survival.

 The researchers who conducted this study discovered that the animal, which once looked much like jellyfish and their ancestors, gradually evolved to lose many of the normal traits that are associated with most multicellular species. H. salminicola's current appearance resembles a series of blobs. Under the microscope, its spores resemble bluish sperm cells that have oval "eyes" and two tails. These "eyes" are stinging cells that help the animal latch onto its host.

 Live Science interviewed evolutionary biologist and co-author of the study Dorothée Huchon, from Tel Aviv University in Israel, who said that over time, the animal have lost its tissue, its nerve cells, its muscles, and "everything." Now, they found that it additionally also lost its ability to breathe. The study has not made clear how the animal could do this, but offered speculation that H. salminicola could survive by leeching its host's energy.