# Do fish get fevers? Cold-blooded defense against viruses and infection.... **URL:** \ **Category:** Factual Questions\ **Created:** [December 30, 2019, 5:33pm UTC](https://boards.straightdope.com/t/do-fish-get-fevers-cold-blooded-defense-against-viruses-and-infection/845604 "2019-12-30T17:33:38Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [December 30, 2019, 5:33pm UTC](https://boards.straightdope.com/t/do-fish-get-fevers-cold-blooded-defense-against-viruses-and-infection/845604/1 "2019-12-30T17:33:38Z")
I was thinking about the role of fever in humans–as I understand it, the temporary suckiness to the organism is still worth it to make the host less hospitable to viruses and, in ways I understand even less, benefits our systemic physiological response to infection. So this OP is based on my understanding that thermal regulation just isn’t A Thing for cold-blooded creatures, which is undoubtedly over-simplified. Given that, an alternative question as subject header (with viruses in mind) might be “Do fish catch colds? And then what?” Can anyone talk about fever, I guess, more generally, in light of my (mis)understanding of cold-blooded biology? Hell, any veterinarian comments on fish with snivels is good too. \*Somewhere/somewhen in SD is my OP “Do tapeworms sleep?”, to which IMO this OP may turn out to be a worthy companion. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [December 30, 2019, 5:48pm UTC](https://boards.straightdope.com/t/do-fish-get-fevers-cold-blooded-defense-against-viruses-and-infection/845604/2 "2019-12-30T17:48:46Z")
As you say, fish are cold-blooded (ectothermic). Their body temperature is essentially that of the water they’re swimming it. A fish can’t run a fever. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [December 30, 2019, 5:59pm UTC](https://boards.straightdope.com/t/do-fish-get-fevers-cold-blooded-defense-against-viruses-and-infection/845604/3 "2019-12-30T17:59:35Z")
So have viruses figured out, evolutionarily, that cold-blooded animals are terrific hosts, and fish can a ton of them? Or since fish have no thermal “defense” against them except simply dying, which does viruses no good, so the opposite is true? I guess I should have made the OP lead, “do fish catch colds?”…because I figured they don’t get fevers. Add to that I have no clue as to the fantastic back-and-forths in the virus-host struggles in any animal besides this one datum of thermal situations. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [December 30, 2019, 6:04pm UTC](https://boards.straightdope.com/t/do-fish-get-fevers-cold-blooded-defense-against-viruses-and-infection/845604/4 "2019-12-30T18:04:42Z")
Fish do attempt to raise their body temperature in response to infection - behaviorally, by moving to warmer water or increasing activity. > [@](#): > > Ectotherms as diverse as reptiles, fish, and insects raise their core temperature during infection through behavioural regulation, which leads to their seeking warmer environments (despite the risk of predation) or, in the case of bees, raising the local temperature of the hive through increased physical activity… the correlation between infection and increased temperature extends even to plants, which arose 1.5 billion years ago. For example, the temperature of the leaves from the bean plant Phaseolus vulgaris increases by around 2°C following infection > **[Fever and the thermal regulation of immunity: the immune system feels the heat](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4786079/)** > > Fever is a cardinal response to infection that has been conserved in warm and cold-blooded vertebrates for over 600 million years of evolution. The fever response is executed by integrated physiological and neuronal circuitry and confers a survival... And, of course, raising body temperature is only _one_ way to fight infection. Fish have a sophisticated immune system. > [@](#): > > Adaptive immunity arose early in vertebrate evolution, 450 million years ago between the divergence of cyclostomes and cartilaginous fish. The fundamental immune molecules, which include Ag-recognizing lymphocytes, immunoglobulins (Abs and Ig-family TCR), MHC products, and recombination-activating (RAG) 1 and 2 genes and the recombination mechanisms (cause of diversity in TCRs and Igs) are similar in fish and mammals. [https://www.sciencedirect.com/science/article/abs/pii/S0165247812001885](https://www.sciencedirect.com/science/article/abs/pii/S0165247812001885) ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [December 30, 2019, 6:05pm UTC](https://boards.straightdope.com/t/do-fish-get-fevers-cold-blooded-defense-against-viruses-and-infection/845604/5 "2019-12-30T18:05:06Z")
> [@markn\_1](#): > > As you say, fish are cold-blooded (ectothermic). Their body temperature is essentially that of the water they’re swimming it. A fish can’t run a fever. Well, not all fish. Tuna can elevate their body temperature through the effort of swimming at high speed. You could call it a fever in some sense of the word but it’s not due to illness. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [January 1, 2020, 6:36pm UTC](https://boards.straightdope.com/t/do-fish-get-fevers-cold-blooded-defense-against-viruses-and-infection/845604/6 "2020-01-01T18:36:00Z")
I call that a band from the late 1960s. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [January 1, 2020, 10:07pm UTC](https://boards.straightdope.com/t/do-fish-get-fevers-cold-blooded-defense-against-viruses-and-infection/845604/7 "2020-01-01T22:07:35Z")
> [@Leo\_Bloom](#): > > Somewhere/somewhen in SD is my OP “Do tapeworms sleep?”, to which IMO this OP may turn out to be a worthy companion. Here ya go: [Do Tapeworms Sleep?](https://boards.straightdope.com/sdmb/showthread.php?t=737221)