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Scientists Discover the First Warm-Blooded Fish

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The unique thing about the moonfish isn’t the fact that it's as big as a car tire or comically round. It’s its blood. The opah, or moonfish, is the first species of fish identified by scientists that’s warm-blooded. 

While tuna and some sharks can temporarily retain a bit of heat in the muscles they use for swimming [PDF], their bodies aren't fully warm-blooded. By contrast, the camera-shy and relatively little-studied opah keeps its whole body, especially its brain, at temperatures higher than its surrounding environment, as researchers from the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center in California discovered. This, they write in the journal Science, makes the opah “distinctively specialized to exploit cold, deeper waters” up to 1300 feet below the surface. 


Blood vessels carrying warm blood from the fish’s heart are located directly next to those that carry cold blood in the gills, forming a counter-current heat exchange that works kind of like a car radiator. The warm blood from the fish’s core helps warm up the cool blood that has been closer to the cold water in the gills (where it absorbs oxygen).  

This makes the big fish a fearsome predator. Thanks to the warm blood flowing throughout its body, it likely has better eye and brain function than its cold-blooded counterparts. While most other fish in cold environments move relatively sluggishly, the moonfish is active and agile, with more muscle power and stamina to chase down its deep-water prey. 

[h/t: Science Daily]

All images courtesy NOAA Fisheries/Southwest Fisheries Science Center

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Animals
Listen to the Impossibly Adorable Sounds of a Baby Sloth
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RODRIGO ARANGUA/AFP/GettyImages

Sometimes baby sloths seem almost too adorable to be real. But the little muppet-faced treasures don't just look cute—turns out they sound cute, too. We know what you're thinking: How could you have gone your whole life without knowing what these precious creatures sound like? Well, fear not: Just in time for International Sloth Day (today), we have some footage of how the tiny mammals express themselves—and it's a lot of squeaking. (Or maybe that's you squealing?)

The sloths featured in the heart-obliterating video below come from the Sloth Sanctuary of Costa Rica. The institution rescues orphaned sloths, rehabilitates them, and gets them ready to be released back into the wild.

[h/t The Kid Should See This]

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