It is one of many aspects of the fish mind mentioned in the article; things like developing memories, comparing oneself to other fish, exhibiting preferences, etc. Each of them alone may not be enough to argue &quot;fish have feelings&quot; or &quot;fish can think&quot; or &quot;fish are sentient beings&quot;, but they <i>are evidence</i> of those things. They don&#x27;t make it so, but they hint at something that it is hard to figure out without a number of data points.<p>Occam&#x27;s razor can just as easily be applied here to come to a conclusion that is opposite your conclusion.<p>Fish do things that mammals (humans) do. We know that mammals do those things (stress fever) because they are experiencing things in a way at least somewhat comparable to the way we experience them (they are experiencing discomfort and fear and their body is responding to it, just as ours do). What is the simpler explanation here?<p>1. Your conjecture that fish are utterly and completely different from other living things that exhibit this response and that they are exhibiting this response for reasons unlike our reasons (i.e. they aren&#x27;t experiencing discomfort and fear, but are still heating up like we do).<p>2. They&#x27;re more like other sentient beings than we&#x27;d previously assumed, and are experiencing things in some ways similarly.<p>In short: If you&#x27;re coming at this with the strongly held belief that fish are impossibly different from humans and can&#x27;t possibly have feelings, you would interpret your way. But, if you&#x27;re coming at it with no strongly held beliefs on the subject, and you see a fish behave in ways that indicate they are sentient and experience suffering like other animals...well, you assume the responses and behaviors are because they are kinda like those other animals.<p>Your assumption (that this response has no relation to the similar response in mammals) requires a <i>new</i> explanation for why the response happens. Thus, it seems to not be the simplest explanation (to me).