# Fish and water temperature

**URL:** <https://boards.straightdope.com/t/fish-and-water-temperature/250314>\
**Category:** Factual Questions\
**Created:** [June 14, 2004, 5:30pm UTC](https://boards.straightdope.com/t/fish-and-water-temperature/250314 "2004-06-14T17:30:01Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [June 14, 2004, 5:30pm UTC](https://boards.straightdope.com/t/fish-and-water-temperature/250314/1 "2004-06-14T17:30:01Z")

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What makes tropical fish tropical in that they die in cool water?  
Why can goldfish live under ice while their relatives koi cannot?

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**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [June 16, 2004, 2:39am UTC](https://boards.straightdope.com/t/fish-and-water-temperature/250314/2 "2004-06-16T02:39:51Z")

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Bump, gosh darn it.

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**Author:** ![Rikster](https://avatars.discourse-cdn.com/v4/letter/r/e9a140/32.png) [@Rikster](https://boards.straightdope.com/u/Rikster)\
**Post date:** [June 16, 2004, 2:52am UTC](https://boards.straightdope.com/t/fish-and-water-temperature/250314/3 "2004-06-16T02:52:02Z")

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Koi live just fine under the ice as long as there is still unfrozen water under the ice. You do have to watch out for a toxic buildup of harmful gases that can acumulate under the ice so it is best to try to keep a hole open for them.  
mind you I am talking about a backyard pond which is what I think you were refering to

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**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [June 16, 2004, 3:42am UTC](https://boards.straightdope.com/t/fish-and-water-temperature/250314/4 "2004-06-16T03:42:11Z")

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> [@Rikster](#):
>
> Koi live just fine under the ice as long as there is still unfrozen water under the ice.

Well, yeah, but then they aren’t living under ice. Goldfish do, and why?

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**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\
**Post date:** [June 16, 2004, 3:48am UTC](https://boards.straightdope.com/t/fish-and-water-temperature/250314/5 "2004-06-16T03:48:24Z")

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> [@carnivorousplant](#):
>
> Well, yeah, but then they aren’t living under ice. Goldfish do, and why?

Oops, sorry. I misread your post to be “Water not frozen over”.  
The Aquarium fish magazine guy, Meyer, says Koi can’t live under a frozen surface.

Again, I apologize.  
So why do tropicals die at 50F?