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  • Hey smart people, Joe here.

  • Have you ever heard the phraseto drink like a fish?”

  • Well, unless you're a ocean dwelling species, that probably means staying sober.

  • Because freshwater fish don't drink!

  • Saltwater fish on the other hand?

  • They're constantly drinking.

  • But if some fish drink all the time and other fish don't drink at all, we're left with

  • an obvious question: Do fish pee?

  • Whatyou've never wondered that?!

  • Water is essential to life as we know it.

  • To keep their chemistry running smoothly, living things need just the right amount of

  • water in their bodies.

  • You'd think that fish have it made when it comes to staying hydrated, but it's not so easy.

  • Fish gills lets oxygen flow into their bodies, but they're also letting water constantly escape.

  • Ocean water is *saltier* than the inside of fish.

  • So water wants to move from the inside out to balance that out.

  • That's a problem if you're a fish who wants to stay alive.

  • It's a process called osmosis, and we can demonstrate that with these eggs.

  • I've dissolved the shells away, leaving a membrane that'll allow water to pass through.

  • One is covered in pure H2O.

  • And one goes into sugar syrup.

  • The syrup contains lots of sugar molecules, and not much water, so water passes out of

  • the egg to balance it out, and the egg shrinks!

  • Life is all about balance.

  • Now, we keep the salts and dissolved chemicals in our blood balanced by flushing the extra

  • through our kidneys, and by drinking fresh water when we're thirsty.

  • But ocean fish only have one option: drink salt water in order to get the H2O they need to stay alive.

  • And most of them do that a *lot*.

  • But they need to get rid of the salt without dehydrating, which they do using special cells

  • in the gills that pump out the extra.

  • Ocean fish only make a tiny amount of urine, and what little pee they make is almost as

  • salty as the pool they pee in.

  • Freshwater fish have the opposite problem.

  • Their insides are saltier than where they live, so water is constantly leaking *in*

  • through their skin and gills.

  • It's just like the naked egg we put in pure water.

  • The inside of the egg is saltier than the water around it, so water flows in

  • and the egg swells up!

  • Plus, they get even more water from their food.

  • So even in their wet world, they never have to take a drink.

  • Freshwater fishes have to *get rid* of water constantly to keep their cells from bursting,

  • which means they pee *a lot*.

  • They're pretty much peeing all the time.

  • If I peed as much as a freshwater fish, I'd release up to 28 liters a day, which is about

  • 20 times more pee than I usually make.

  • For fish, peeing in the yard is a big help to their neighbors.

  • Fish pee is full of ammonia, a nitrogen containing compound, and phosphorous, both nutrients

  • that plants crave.

  • These also help feed algae and coral reefs, like a liquid fertilizer that helps keep aquatic

  • ecosystems healthy.

  • Fish are little swimming, urinating, nutrient recycling plants.

  • Some fish get crazy with this salt-and-water balancing act.

  • Some are able to live in water so salty it's hard for them to even stay below the surface.

  • Others, like salmon, can tweak their body chemistry to move between salty and fresh water.

  • Sharks and their relatives are especially weird when it comes to salt balance.

  • Using a special enzyme, they stuff ureaanother nitrogen containing compoundinto their tissues.

  • By loading their insides with another ion, they keep water from wanting to rush out of their bodies.

  • It's also why their meat smells like pee.

  • Thankfully, we (sniff sniff armpit) don't do that.

  • I smell great.

  • But we do owe our ability to regulate water and salt to our fishy ancestors.

  • Scientists think that a healthy salt level for the bodies of most living animals is about

  • the same concentration as the ancient oceans where life began.

  • You even have evidence of this in your body.

  • Before we're born, human embryos develop three different types of kidneys.

  • Two get absorbed, and one eventually becomes the final pair.

  • The extra organs are an evolutionary leftovers: early kidneys that we also see in primitive

  • fish, who use it to balance their salty bodies.

  • It reminds me of the famous poem by I.P. Freely:

  • Tinkle tinkle, little fish Homeostasis is what you wish

  • The ocean's your toilet, and even though you soil it

  • Urea-ly have mastered your niche.

  • Stay curious.

Hey smart people, Joe here.

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B2 US fish water pee salt freshwater egg

Do Fish Pee?

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    Liang Chen posted on 2019/04/30
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