Is it possible for a multicellular living creature to have no need to intake oxygen or some other gas?

So this question came to mind when I was pondering the plausibility of space-dwelling life forms. I did some research and I came to the conclusion that living creatures as we know them need oxygen (or in a grander scale some sort of gas) to help them grow, produce energy, break down food, and basically to just function.

It turns out the only animal on earth that doesn’t need to intake oxygen is the henneguya salminicol which is a small parasite that lacks a mitochondria. It is presumed it gets its energy from its host but it’s still unclear.

This led me to thinking that there could be alternative ways to produce energy rather than breathing in air. Perhaps it is as simple as consuming more nutrients through food or more complex like having a specialized mitochondria-like cell that achieves this in whatever way that might be possible.

So in short, is it possible for multicellular living creatures of all shapes and sizes to lack the need to intake oxygen or some other gas, if so, how would they achieve this feat?

  • $\begingroup$ Yes, lots of animals do this, those that are small enough to simply absorb all the oxygen they need directly through their tissues, they can be quite big as long as they're small enough in cross section (long and thin) did you want something bigger? $\endgroup$
    – Pelinore
    Jan 21 at 3:39
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    $\begingroup$ When other folks build answers using the common definition of "breathing" -- instead of what you really intend (no oxygen exchange at all), you will get answers that you seemingly won't find useful. They are not wrong -- they are simply not clairvoyant. I suggest you edit your question to clearly use the proper terms for what you actually seek. You will get more useful answers. $\endgroup$
    – user535733
    Jan 21 at 9:08
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    $\begingroup$ The "plausibility of space-dwelling life forms" in sentence 2 makes it rather clear what is meant by no breathing $\endgroup$ Jan 21 at 16:03
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    $\begingroup$ Ditto what user535733 said. Because fish don't breath. Don't make people guess what you intend, or waste time drafting an answer you don't like. Use the correct words to describe exactly what you mean. If you mean "don't require oxygen" use the phrase "don't require oxygen" instead of "breath", which as you admit means exchanging oxygen in the air through lungs. DV for lack of specificity. $\endgroup$ Jan 21 at 16:55
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    $\begingroup$ Oxygen? or gas? They are not necessarily the same thing. Fish require oxygen, but they do not consume it as gas. They extract dissolved oxygen from the water in which they swim. Also, not sure if this is relevant or not, but there are salamanders living under my deck that require oxygen (gas) from the air, but they do not breathe it. They absorb oxygen through their moist skin. $\endgroup$ Jan 23 at 20:50

7 Answers 7


Strictly anaerobic.

I proposed a giant sea creature that would not need to breathe because it metabolized its food using anaerobic glycolysis.

Could a deep ocean creature use some kind of bacteria in its body as a way to generate oxygen?

But here is another idea for your creature as regards oxygen: it minimizes its use of oxygen by using anaerobic metabolism. When humans do this it is https://en.wikipedia.org/wiki/Anaerobic_glycolysis Energy can be derived from glucose without oxygen in short bursts. Lactate is the end product and builds up - this is the burn you feel when you feel the burn. Ultimately the liver has to oxidize the lactate when there is oxygen around again. It is an inefficient use of sugar compared to aerobic metabolism but we can do it.

But what about a creature that did anaerobic glycolysis and then ignored the end product? Yeast do exactly this - the end product is ethanol and it just builds up until they cant stand it any more. Or it evaporates away. A sea monster with lots of food and little oxygen could just let the lactate waste product ooze out of its pores into the water. It would need a lot more food (I think three times as much?) than a comparably sized creature using oxidative glycolysis, which extracts more energy from the sugar. But it could get by with much less oxygen.

This is how tapeworms do it - they don't breathe or need much oxygen which is good because there is not much to be had in the hot poopy gut. They do anaerobic glycolsis and dump their wastes back in the fecal stream. The sea monster would be similar.

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    $\begingroup$ @HomegrownPotatoes: Initially when life began on Earth there was no free oxygen. All life was anaerobic. A billion years later, some new disruptive organisms evolved, which found a way to synthesize sugars from carbon dioxide and water and sunlight, releasing oxygen as a waste product. The newly available free oxygen promptly started to oxidize everything that could be oxidized, and began accumulating in the air. It was the deadliest mass extinction ever. $\endgroup$
    – AlexP
    Jan 21 at 0:18
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    $\begingroup$ @HomegrownPotatoes - you do not need oxygen for anaerobic glycolysis. Worms get by without. $\endgroup$
    – Willk
    Jan 21 at 3:20
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    $\begingroup$ There are three types of anaerobic organisms. There are strict anaerobes (oxygen deadly for them, they are mostly single-cell), oxygen-tolerant anaerobes (oxygen useless, but not much poisonous either, these are mostly single-cell as well) and opportunistic anaerobes (use oxygen when available, but can live without it, these range from bacteria all the way to some fish species). Be aware that the anaerobic glycolysis yields like 10x less energy than the aerobic path and also releases much more unwanted waste (ethanol + carbon dioxide or lactic acid being the most common). $\endgroup$
    – fraxinus
    Jan 21 at 9:22
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    $\begingroup$ @AlexP en.wikipedia.org/wiki/Holocene_extinction $\endgroup$
    – user253751
    Jan 23 at 15:15
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    $\begingroup$ @user253751 We are currently in a mass extinction event, yes, but the Great Oxygenation Event is theorized to have killed 80%-99% of all life on Earth. Just because they were microbes does not make them any less diverse as species. It truly was the closest life ever got to being completely wiped out; the other mass extinctions are peanuts compared to the GOE. $\endgroup$
    – Thegs
    Jan 23 at 22:06

This led me to thinking that there could be alternative ways to produce energy rather than breathing in air.

Of course there are. There are small sealed glass balls for sale with plants inside, closed ecosystems which only require light. The sealed glass ball does not breathe anything at all.

Your creature could have large transparent skin sacs filled with symbiotes that would convert sunlight, or maybe even hard radiation (like D. radiodurans), into energy-rich chemical compounds.

Of course then the creature would still need to eat in order to grow and repair itself.

It could have evolved on a moon that was gradually losing atmosphere while orbiting around its primary. Over the aeons, the organism adapted to lower and lower pressures, until it grew skin sacs large enough to replace breathing altogether. Some more hundreds of thousands of years later, the moon grew so close to its primary that began disintegrating. The creature was already vacuum-proof at that time, and had developed zero-g instincts, so it readily adapted to life in space: long periods of dormancy to save energy, looking for small asteroids with ice and minerals.

It would land on an asteroid, and start crushing the rubble of carbonaceous chondrite and volatile ice to "digest" them like plants would. Its "stomach" would be more akin to a small greenhouse, and the creature would in essence eat earth. Waste material and useless rock fragments would be stored and used as reaction mass to navigate in space.

  • $\begingroup$ +1 for the creativity, but remember the question wasn’t about space-dwelling life. $\endgroup$ Jan 21 at 0:27
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    $\begingroup$ @HomegrownPotatoes sorry, I'm not sure I understand - didn't you write «I was pondering the plausibility of space-dwelling life forms»? However, this kind of setup (minus the need to resist vacuum and move in zero-g) would also work for a land-dwelling creature (it wouldn't underwater - there, you need to predate other organisms and Willk's answer is way better). $\endgroup$
    – LSerni
    Jan 21 at 0:47
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    $\begingroup$ The plants in those sealed balls do breathe, It just happens that they consume at night what they produce at day. $\endgroup$
    – L.Dutch
    Jan 21 at 6:08
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    $\begingroup$ @L.Dutch It sounds like the question you're trying to ask "Is it possible for a living creature to not use oxygen at all". Which is very different to "not having to breathe". If that's the case you should make a new question and be more specific in what you're looking for. $\endgroup$
    – Kaz
    Jan 21 at 7:38
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    $\begingroup$ @L.Dutch yes, the plants breathe, but the whole ensemble does not. Likewise, we humans do not need some substances in our diet even if they are essential to our metabolism, because they get produced from other substances by gut symbionts. So the overall organism (human plus gut bacteria) can "do without" those substances (until a gut infection kills off enough symbionts to send us into some deficiency). In my scenario, the "overall organism" does not need to breathe because it has plant symbionts that take care of that. $\endgroup$
    – LSerni
    Jan 21 at 19:36

Anerobic bacteria get by just fine without oxygen.

According to the laws of thermodynamics, the driving force of change in a system is disorder, which must always increase. There are two ways of doing this in a chemical reaction. One is to produce heat, which makes the surroundings vibrate, thereby increasing disorder. The other way is to increase disorder in the reaction products, typically by increasing the number of molecules, especially when these are gases.

The equation for anaerobic respiration of glucose is as follows:

C6H12O6 ---> 3CO2 + 3CH4

This is typical of the reactions that occur in digesters to produce biogas.

It's a very inefficient way of using glucose (because a lot more energy can be released by burning the methane produced) but it does work and could work fine in space.

In fact, this reaction is being carried out by bacteria in your gut right now.

Multicellular organisms are perfectly possible, especially around undersea hydrothermal vents. For example https://en.wikipedia.org/wiki/Loricifera

There are also plenty of non-gaseous oxidants other than oxygen that a space-dwelling organism could use. These include nitrates, chlorates and peroxides. The biggest difficulty for life in outer space is that liquid cannot exist in a vacuum. In a vacuum, all liquids evaporate, leaving just solids. Several bodies in the solar system have an ice crust which imparts enough pressure to allow a liquid ocean below the surface. One such body is Europa, a moon of Jupiter, which has a thin atmosphere of oxygen. This results from photolytic decomposition of H2O, with the hydrogen escaping into space as it is much lighter than the oxygen.


May depend on your definition of breathing. My first thought was the fish; however absorbing oxygen directly from seawater (pumped through gills) still meets your definition of breathing, and correctly so, given your need to dwell in space.

My second thought was to remain underwater, but to look at the relatively new development of Air Independent Propulsion (AIP) in submarines. These allow long submerged range and good performance, without nuclear power, and have shown themselves to be embarrassingly effective in NATO exercises.

Most AIP submarines "drink" and store liquid O2, not exactly compatible with the chemistry of living beings we know, though maybe space dwellers have evolved with at least some organs running at suitably lower body temperatures.

However a few (submarines) have been developed to use other oxidisers such as (liquid) hydrogen peroxide. The fact that HMS Explorer was known within the Senior Service as "HMS Exploder" hints at the difficulties even in a submarine, let alone the stomach lining chemistry of a creature capable of drinking peroxide...

Either way, instead of breathing, the creatures need to drink some suitable oxidiser. This may not be naturally available. If not, is it possible for your beings to evolve alongside other races in a symbiotic fashion?

Perhaps they evolved alongside future humans or other technological races, capable of bottling peroxide or liquid O2, in return for some services from the creatures, perhaps as messengers, or as grazers of the asteroid belt, shitting nickel and lithium as they chug down another bottle of oxidiser.

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    $\begingroup$ Agreed. Most commonly, to release energy, things (living or not) use bipropellant methods, i.e. a combination of fuel (i.e. ATP from food in animals) and an oxidizer (often oxygen, but peroxide etc. are also available as noted). There is nothing stopping a creature for storing both fuel and oxidizer, instead of storing one of them and continuously ingesting other. Or even continually ingesting both! One could also be combining more than two substances (multipropellent) to release energy, as well as using one only substance (see monopropellants $\endgroup$ Jan 21 at 16:35

The fundamental problem here is that almost no life on Earth works this way because it's very inefficient. Oxygen is by far the most energetic oxidizing agent available and thus anything using it in it's cycle has a huge competitive advantage over anything that doesn't.

Thus you have to look at environments in which there is no gas to be had to find a metabolic sequence that doesn't use it. We have some gut-dwelling stuff that would provide a basis for zero-gas metabolism.

However, this misses the fundamental issue--you don't need a zero-gas cycle for your space-based life! Rather, you need to think like a rocket rather than a jet--bring everything you need to the table. Obtaining matter is going to be a big problem for space-based life because it's in an environment with very little of it. Thus any worthwhile space-based life must do it's utmost to hold onto everything it gets except those elements it gets an excess of that it can't make use of. (Likely an issue with hydrogen--it's available in the solar wind but your life will have little to react it with.)

You can use the normal photosynthesis and oxidation cycle of Earth-based life, just keep the gasses inside the creature. The sunny side reduces CO2, the shady side oxidizes the carbon.


living creatures as we know them need oxygen

This is very untrue (as you indeed acknowledge). Anaerobic life is common. Even humans and other higher mammals have many anaerobic metabolic pathways. In fact, all life on earth was anaerobic until 2.4 billion years ago, whereas life has been around for at least 3.7 billion years. In some ways, anaerobic life is the norm, and metabolism that uses oxygen is a strange innovation.

But moving on from that, supposing these fictional organisms are aerobic. Cutaneous respiration is common in many organisms, especially amphibians. It has been measured (PDF), and counts for 100% of the oxygen of the lungless salamander, and 90% for the Lake Titicaca water frog.

Note that having only cutaneous respiration limits the bulk of these fictional organisms. (Because of reasons to do with the amount of surface area feeding the amount of body.) There are no big amphibians. If your fictional beings are big, they'll have to be thin like a big pancake.

"Aerobic metabolism is the most efficient way of producing ATP by producing 18 times more ATP for each molecule of glucose than anaerobic metabolism." – so your fictional anaerobic beings will need about 18 times more food to do the same amount of work, or eat the same amount of food we do but be 18 times smaller/lazier.


Here's the problem: here on Earth nearly all living things require oxygen because it's the most convenient, plentiful, and non-toxic oxidizing agent. Oxidation could realistically be called the center of the living universe. No oxidation, no life (insofar as we know and understand life today). It does a lot more than just make energy. Oxidation is needed for decomposition, to fight pathogens, for all kinds of things.

Which means that unless you walk away from describing the internal workings of your creature (honestly, most authors don't explain the inner workings of things for a reason), you either need to replace oxidation with something that can be found in outer space or you need to explain how you're getting enough oxygen. Why? Because oxygen is consumed in the oxidation process and I'm not a good enough chemist to suggest a way that it can be recycled (which would likely break the laws of thermodynamics, anyway).1

It's true that many things other than oxygen can be used as oxidizers. The problem is that most of those things are toxic for one reason or another. Yikes!

So, I'm going to ignore the tag and go with instead

Let's combine some things we know and see what imaginative fiction we can come up with.

  1. At the bottom of the ocean, there's little to no free oxygen. That means there are a whole host of creatures that have to make do or go without. From that linked source we learn:

the giant red mysid (Gnathophausia ingens) continues to live aerobically (using oxygen) in OMZs. They have highly developed gills with large surface area and thin blood-to-water diffusion distance that enables effective removal of oxygen from the water (up to 90% O2 removal from inhaled water) and an efficient circulatory system with high capacity and high blood concentration of a protein (hemocyanin) that readily binds oxygen.

Another strategy used by some classes of bacteria in the oxygen minimum zones is to use nitrate rather than oxygen, thus drawing down the concentrations of this important nutrient. This process is called denitrification.

What this tells us is that a good space creature design would be one that uses oxygen with enormous efficiency.2

  1. The universe is filled with plasma. I'm actually having trouble finding details about what kinds of atomic plasma can be found out there, but the reality is that oxygen plasma can be one of those wonderful atoms. From that link we learn...

The magnetosphere provides a barrier between our planet and particles continually given off by the Sun's corona called the "solar wind." These particles constitute a plasma - a mixture of electrons (negatively charged) and ions (atoms that have lost electrons, resulting in a positive electric charge).

Sure, that plasma is proverbial as hot as the nether foundations of Lucifer's kitchen! But all the electrons and atoms you need (given massive efficiency!) are out there. Well.. OK, there's not a lot of them. But that's one of the reasons I'm shifting to the tag.

  1. Finally, there are creatures who require oxygen that can't get enough of it from the depths of the ocean. One famous example is a whale, which must periodically surface to get the oxygen it needs.

I give you Vernaculus Solanum Tuberosum Balaenus3

Your creature needs oxygen like pretty much every other form of life. But it has:

  • The most evolved oxygen efficiency in the known universe,
  • The ability to supplement its oxygen by recombining the electrons and atomic nuclei in Solar Wind (the heat is used to aid in other things, like digesting wayward spaceships),
  • The capacity to store an unearthly amount of oxygen,
  • And the periodic need to skim oxygen from venting comets and unsuspecting planets.

And when the natives of an otherwise perfectly peaceful world see a school of those whammer-jammers coming in to suck down a little prime oxy... oh, yeah... whole religions are born.

1That's not completely true. As an EE I can tell you that you could use solar power (saving the laws of thermodynamics) to break apart oxidized compounds to free the oxygen to be used once again as an oxidizing agent. However, I consider that line of reasoning a great deal less believable than what I'm going to explain next. A chemist might know better than I, but I don't know of any animal solar-accumulating-break-oxygen-apart anythings. That's why I'm skipping this potential solution.

2You could legitimately convert from oxygen to nitrogen based on the fact that some bacteria use nitrogen rather than oxygen. But I suspect there's not a whole lot more nitrogen in the vast reaches of space than oxygen, so you're basically back to the same solution I'm offering, other than the supplies of nitrogen are a whole lot smaller than of oxygen. Weird, that....

3That's likely the worst Latin translation in history and I can easily imagine Latin enthusiasts laughing for weeks and Latin professionals closing their Worldbuilding accounts because of it. It loosely translates to: The Homegrown Potato Whale.

  • $\begingroup$ Wait... You don't know of any biological system which can use solar power to break apart oxidized compounds to free the oxygen to once again be used as an oxidizing agent? Have you heard of photosynthesis? $\endgroup$
    – brendan
    Jan 23 at 14:41
  • $\begingroup$ @brendan I have heard about photosynthesis! The chemical reaction is 6CO2 + 6H2O → C6H12O6 + 6O2, which frees up oxygen. But that doesn't completely work. Explaining the CO2 is easy, but explaining where the water is coming from isn't. Besides, there are some serious problems with a plant in outer space, which is why I ignored it. It is my fault that I used "biological" rather than "animal." I'll go change that. $\endgroup$
    – JBH
    Jan 23 at 18:30
  • $\begingroup$ I'm not sure why the CO2 is easy to explain but the water isn't. Both of them are products of respiration, which is just the same chemical reaction as photosynthesis in reverse. Both of them are easier to find in space than dioxygen gas, and in fact I would tend to think that water is easier, since it forms solid chunks anywhere past the snow line. And there are some photosynthetic animals. Yes, they do this by ingesting/capturing algae which actually do the photosynthesis, but this is in a sense how plants do it as well; chloroplasts are descended from captured blue-green algae. $\endgroup$
    – brendan
    Jan 24 at 11:01
  • $\begingroup$ @brendan CO2 can be (and probably is) a natural consequence of energy processing. In humans, we take in O2 and exhale CO2. That CO2 isn't a function of the lungs so much as it's a byproduct of processing the O2. That's why it's easy to explain - the creature would produce it. Water, on the other hand, won't be created by the creature unless it's burning O2 and H to get it (tough to sell that one). I'm not sure water can be found in space that easily. Planets, atmosphere, comets, but not space (hence my desire for the whale to dip into atmospheres from time to time). $\endgroup$
    – JBH
    Jan 25 at 1:13
  • $\begingroup$ Note that plants don't create water through photosynthesis, that's not part of the equation. Plants derive water a bit from the atmosphere, but primarily via their roots. All that's why I assert water is the problem. But, if you shift to science-fiction, water can be found in lots of places. $\endgroup$
    – JBH
    Jan 25 at 1:13

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