Emily Yeager

Emily Yeager

Nov 02, 2022

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Sharks do it differently: All about shark pee

Have you ever found yourself sitting at the beach or scrolling through your phone and suddenly thought: "I wonder how sharks pee?"

No? Well I bet you're thinking about it now!

I know, I know, it's a bit taboo. But we all do it. In fact, we need to pee to allow our body to function properly.

When we pee, our body is getting rid of excess water, waste and toxins. So, wouldn't any organism that acquires excess toxins, waste, and water in it's body need a way to remove it?

Yes! All organisms that eat, need to get rid of waste but the way they go about removing that waste is different.

Unlike us, sharks live in a saline (or super salty) environment. Because of the salty nature of their environment, they don't have excess water like us--in fact, they had to evolve a unique way to retain water inside of their bodies.

Sharks produce a substance called urea (a collection of salts) that they store in high concentrations in their tissues and bloodstream to help retain water.

Why do they need to do this?

Have you ever licked salt off your hand (or gotten a mouthful of it)? You may have noticed that, after eating the salt, you got thirsty. That happened because of something called osmosis--or the (spontaneous) movement of water from places of lower salt concentrations to places of higher salt concentrations.

Since sharks live in a salty environment, the water in their bodies naturally wants to move from places of low salt (inside of them) to places of high salt (the ocean surrounding them). By maintaining urea inside of their tissues, sharks increase the amount of salts inside of their body relative to their surrounding environment--preventing water from leaving them.

So sharks have urea (named appropriately like urine as it serves a similar function) that they store in their bodies--how do they get rid of it?

The short answer--through their skin!

Sharks maintain high concentrations of urea in their bodies to prevent water loss and thus don't need to get rid of it regularly.

But what happens if the urea concentration gets too high or the salty environment they live in becomes less salty (yes, some sharks do travel into more freshwater environments)?

They excrete it!

(Like pee, you ask? Not quite)

As sharks don't have excess water in their systems like us, they don't make the same watery urine that we do. Instead, they have been shown to get rid of urea (or excrete it) through their bodies (and gills).

And, the urea that they excrete is measurable--which is why we want to study it!

Shark urea uptake and excretion. Sharks take up salts from the environment through their gills and distribute it through their muscle tissues and bloodstream as urea, Urea allows sharks to osmoregulate in highly saline environments. When the environment changes (or the shark is stressed), urea can then be excreted through the shark's gills or skin. Infographic created by Emily Yeager on BioRender.

So, do sharks pee? Yes, sort of.

How do they do it? Through their skin and gills!

Why do we want to study it? Well, beyond being able to say we study shark pee, urea can tell us a lot about shark physiology and how osmoregulation (or the management of water/salt balance within the body) changes by shark species, environment, and capture/release stress.

Do you now know more than you ever wanted to about shark pee? Perhaps, but I hope not!



Thank you so much for taking the time to read this lab note! We are in our final stretch of fundraising so, if you want to help us study shark pee, please feel free to support our research! To everyone who has donated so far--THANK YOU, this research wouldn't be possible without you.

Have more questions or want an explanation of another part of our project? Feel free to send us a note or ask in the comments section!




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About This Project

Sharks use solutes, such as urea, to prevent cellular water loss. While the mechanisms of urea retention are well studied, no studies have accessed urea loss in the field or across multiple species. This study will provide insight into how sharks moderate water loss by collecting non-invasive urea samples from the shark gill interface. This project will allow us to determine urea concentrations at the surface of shark gills and to better understand how sharks use urea to control water loss.

Blast off!

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