It seems that the majority of alien species in Star Trek breathe oxygen-rich air just like Humans. The Benzites seem to breath some other mixture of gases, and I believe Jadzia mentioned a Hydrogen-breathing alien in an episode of DS9 once. But what's surprising given Star Trek's fascination with sentient aquatic mammals from Earth is the apparent dearth of sentient water-breathing alien species. I can only think of one: the Xindi-Aquatic.

two Xindi-Aquatic in a large tank from from the Xindi council on Enterprise

Are there any sentient water-breathing aliens in Star Trek other than the Xindi-Aquatic?

Earth dolphins and whales are not water breathers, they're just really good at holding their breath. And they're not aliens to boot, so doubly disqualified. I'm not interested in any further commentary on dolphins or whales.

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    Whales are questionable given ST IV: The Voyage Home. I also thought of Bevvox, the massive Bioplasmic organism that is part of the "Think Tank" Voyager encounters in S05E20. Not quite water-breathing, but definitely lives permanently in some kind of "fluid".
    – LevenTrek
    Feb 28, 2018 at 4:19
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    The Enterprise-D did have a Cetacean Ops department - memory-alpha.wikia.com/wiki/Cetacean_Ops - also, in the Titan novels there is a water breathing crew member
    – NKCampbell
    Feb 28, 2018 at 4:44
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    Whales are not water breathing, they breath air. They are disqualified by being air breathing as well as not being aliens. Feb 28, 2018 at 5:58
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    Depending on what you consider canon, there is a highly intelligent dolphin-like species in Diane Duane's Trek Novel Dark Mirror that breathes water. Also, one could speculate that the Antedeans (those fish-like beings from TNG's "Manhunt" probably breathe water at least part of the time. Not sure if there's anything in Trek lore to confirm that, however.
    – Helbent IV
    Feb 28, 2018 at 6:27
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    @steenbergh Odo's species are the sea. Plus they can survive in space (at warp speeds no less) so they don't breath. Feb 28, 2018 at 7:24

5 Answers 5


The Aquans on the planet Argo are water breathers in "The Ambergris Element". But that is an animated episode and so might not be counted by as canonical.

An Aquan male

  • This led me to the memory alpha article on water breathers which only references the Aquans and the Xindi-Aquatics, which leads me to believe that this is the (only) correct answer. I'll accept unless something dramatic is revealed in the next couple hours. Feb 28, 2018 at 6:06

Technically correct answer:

Counselor Troi is a water-breathing alien in the TNG episode 7x19, "Genesis" (at least to the extent that a half-Betazoid is an alien)

enter image description here

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    I'm not sure if this counts. In this episode, she had reverted to an evolutionary ancestor of Betazoids. Not only does that imply that they no longer exist, but there was no evidence that they were sentient. While she was devolving, she was shown acting more like a fish, gasping when taken out of water, and silently slumped over in the small amount of water she had otherwise.
    – forest
    Feb 28, 2018 at 7:56
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    That screenshot is quite disturbing. But this gets my vote. :-)
    – Praxis
    Feb 28, 2018 at 14:26
  • @Praxis: I think the fish-out-of-water gasping is more disturbing, but I can't locate the video Feb 28, 2018 at 16:08

In addition:

Trill symbionts are alien, sentient, and water-breathing.

enter image description here

They originate from natural pools such as in the Caves of Mak'ala ("Equilibrium").

While it is clear they don't need to be submerged all the time to breathe (they can derive respiration from their host and don't appear distressed when exposed to air for a relatively long while), they breed and are born in the pools and they appear completely at ease while submerged in the pools so it appears they are naturally aquatic and water breathers.

enter image description here

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    Cool idea but I'm not convinced that they can actually breathe while underwater. Feb 28, 2018 at 20:01

Going out on a limb here, happy to be proven wrong...

No, the Xindi-Aquatics are the only water-breathing species in Star Trek Canon.

There are species that are almost there, but not quite:

  • The humpback whales of Star Trek IV: The Voyage Home are not quite "water-breathing" (since whales breathe oxygen), but they are water-dwelling.

  • The group that Voyager encounters in S05E20: Think Tank includes a bioplasmic lifeform named Bevvox. He lives permanently in a fluid tank on their ship, but it isn't water.

  • The species that Voyager encounters in S05E09: Thirty Days is an underwater society, but is not quite water-breathing.

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    Key word here is "canon". Another way to say that is "that we know about".
    – Tim
    Feb 28, 2018 at 5:31
  • If you're cataloguing close calls, you should add the Antedians. Feb 28, 2018 at 6:39
  • Thirty Days featured an eel that would have had nothing to breathe except the water, though we saw no evidence of sentience there. Feb 28, 2018 at 12:15

Assuming that aquatic lifeforms use gills to extract oxygen from water I searched Memory Alpha for "gills".

The result:

The Amphibian page lists, among Troy and Paris who have already been mentioned here:

Not many, but the Xindi-Aquatic aren't the only ones.

  • The Betarians were clearly not submerged in water, despite the aesthetic of gills. Feb 28, 2018 at 12:16
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    Yes, Star Trek Discovery is canon, just like every other live-action TV show is, at least from the perspective of those deciding the future of the Star Trek franchise. Anybody who doesn't like that can join all the people who think that Enterprise shouldn't be canon. Feb 28, 2018 at 15:38

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