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Let's say that I had some sort of habitat in a space station or similar structure, which had everything a blue whale would need to survive, but did not have any gravity. How large could a blue whale reach in a zero gravity environment? If allowed to breed and evolve, would they become larger? (The project I am working on isn't actually with blue whales, but I felt like would be a good example of the general concept I'm thinking of, which I could use to make my question more specific) Edit: This question is ONLY using blue whales as an example of "really large animal that could function in an environment with no ground to walk on", and I am only asking about how large they could get without the restriction of gravity, not whether or not they could survive. I do not agree with the sentiment that the ocean is "already pretty much zero gravity", as there is very clearly gravity in the ocean, and even just a little bit of gravity would still have at least some sort of effect on how large an organism could grow. Even if the increase is only a tiny fraction of a percent, I still want to know that.

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    $\begingroup$ They already live in what is effectively a near zero-g environment. And in zero-g, how would they know how to go "up" to the surface in order to breathe? Indeed, would there even be a surface where they could count on there being air instead of water? You might try whale sharks instead: en.wikipedia.org/wiki/Whale_shark $\endgroup$
    – jamesqf
    Aug 11 at 22:20
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    $\begingroup$ (1) Aquatic animals do live in an effectively zero g environment. (2) A closed habitat is in many ways similar to an island; an insular environment can produce both an increase in size and a decrease in size. See insular gigantism and insular dwarfism. $\endgroup$
    – AlexP
    Aug 11 at 22:20
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    $\begingroup$ 1) This question is not about if they could survive in a zero-g environment, it's about how big they could get. 2) I don't think that the ocean is close to zero-g, as there are up and down axis, and creatures are still affected by gravity, just not as much as on land. The idea that "the ocean is already close to zero gravity" just doesn't make much sense to me. Yes, it is affected much less severely than terrestrial environments, but it still has gravity. Even if it's only a few feet of a change in the maximum possible size of an animal, that would still be nice to know. $\endgroup$ Aug 11 at 22:22
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    $\begingroup$ Probably thermal dissipation is ultimate limiter. Processing of food generates heat. An ever large body will require increasingly large amounts of food. However square-cube law says that there will be less surface area to dissipate that heat. They rely on water for cooling, In zero G that might not be as readily available. $\endgroup$ Aug 12 at 0:44
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    $\begingroup$ A whale's biggest challenge isn't beating gravity, is beating its own body (heat dissipation and nutrient circulation to the cells at the end of the capillaries) $\endgroup$ Aug 12 at 11:12
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Absurdly large.

The main limitation on size is gonna be blood flow, and if you don't need to do much energetic stuff, it's not gonna be that hard to evolve some arteries to contract to push blood around.

The main limitation on whale size is food, and if you give them more food if they're larger you could push them to be even more massive.

You'd need to push them.

Blue whales are huge because competition is intense. They use lunge feeding, where they lunge after krill or similar prey to get huge amounts of food. This means they need huge amounts of energy for quick bursts and to have a larger mouth to catch more krill.

There are many more maneuverable or agile predators, but none with as much endurance and size of mouth as blue whales.

If they don't need to be larger to be fed, why would they evolve to be larger?

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  • $\begingroup$ Thank you for an actually helpful answer. That first section of your answer was exactly what I was looking for. $\endgroup$ Aug 26 at 3:53
  • $\begingroup$ Glad to help. Do you need anything else to accept my answer? $\endgroup$
    – Nepene Nep
    Aug 26 at 8:37
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    $\begingroup$ Nope, just accepted it. Thanks for reminding me to do so. $\endgroup$ Aug 26 at 14:53
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You are going to have very strange evolutionary forces if a single species and all it's ancestors never have to lift a fin for food or breeding. Perhaps it just evolves to be as cute as it can so the handlers will give them more food or attention. Sure it could get huge, but I don't think it would be a option all roads must lead to.

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