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Andy Turko, University of Guelph

To Cool Off, This Fish Gets Out of the Water

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Andy Turko, University of Guelph

If you can’t stand the heat, get out of the water. That’s one fish’s strategy, anyway. New research shows that the mangrove rivulus fish (Kryptolebias marmoratus) flings itself onto land when the water gets too hot.

Plenty of fish split their time between surf and turf. Amphibious fish like K. marmoratus and the mudskipper can breathe and scoot around in the water and on land, which gives them an advantage when conditions in either place become uncomfortable or dangerous. 

But even among its weird amphibious brethren, the mangrove rivulus fish is unique. The little fish, which can be found in waters from Florida to Brazil, holds the record for the longest time spent on land. Researchers in South America found K. marmoratus living on land for up to 66 days at a time in crab burrows, beer cans, and even hollow logs. 

“We kicked over a log and the fish just came tumbling out,” one researcher memorably told Reuters

Getting out of the water can be tricky with no arms or legs, but K. marmoratus has it down to a science. The fish flings itself upward like an acrobat and flips, end over end, eventually landing on its belly. From there, it wriggles into a comfortable spot.

Why do they do this? For the same reason we jump into a swimming pool: to cool off. Researchers at the University of Guelph discovered that the fish leave the water when it gets too warm. In a paper published this week in Biology Letters, the scientists reported that the body temperature of an overheated fish drops within a few seconds of the fish leaving the water. It’s called evaporative cooling: as a fish’s wet skin dries, its body temperature drops.

This self-propelled air conditioning is an impressive and important adaptation for the fish, which live in waters that regularly reach 100.4°F.

“If the fish are prevented from jumping out of the water, they would die,” lead author Patricia Wright said this week in a press release.

Wright and her colleagues also found that, given a few days to acclimate, K. marmoratus quickly adapts to warmer water. This will serve the fish well as climate change dials up the heat in waters worldwide.

The ability to adapt is vital in an age of rapidly changing environments. K. marmoratus’s methods may be unorthodox, but they work. In time, we may just find that the weird will inherit the Earth.

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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
Watch a School of Humpback Whales 'Fish' Using Nets Made of Bubbles 

Just like humans, humpback whales catch many fish at once by using nets—but instead of being woven from fibers, their nets are made of bubbles.

Unique to humpbacks, the behavior known as bubble-net feeding was recently captured in a dramatic drone video that was created by GoPro and spotted by Smithsonian. The footage features a school of whales swimming off Maskelyne Island in British Columbia, Canada, in pursuit of food. The whales dive down, and a large circle of bubbles forms on the water's surface. Then, the marine mammals burst into the air, like circus animals jumping through a ring, and appear to swallow their meal.

The video offers a phenomenal aerial view of the feeding whales, but it only captures part of the underwater ritual. It begins with the group's leader, who locates schools of fish and krill and homes in on them. Then, it spirals to the water's surface while expelling air from its blowhole. This action creates the bubble ring, which works like a net to contain the prey.

Another whale emits a loud "trumpeting feeding call," which may stun and frighten the fish into forming tighter schools. Then, the rest of the whales herd the fish upwards and burst forth from the water, their mouths open wide to receive the fruits of their labor.

Watch the intricate—and beautiful—feeding process below:

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