Do Fish Experience Thirst?

human animals are thinking and feeling. You know, exactly when you're thirsty, you might experience a range of symptoms, perhaps dry mouth, fatigue, reduced to your an output, lightheadedness, and weakness, among others. And when you're really really thirsty, like lost in the desert without a canteen type of thirsty, you simply crave water, sometimes to a degree that you can hardly think about anything else. That powerful urge is what

keeps our bodies from becoming dangerously dehydrated. But because we can't put ourselves in a fish's shoes or fins, there's no way for us to know how fish perceive thirst or if they do it all. But we spoke via email with Boston College Assistant biology professor Christopher Kennelly. He said, I think of first as a cognitive response to hydration, and it's hard to get inside of fish's brain. However, we do know quite a bit about how fishes regulate

water balance. Regardless of their thirst, drive or black thereof, these creatures absolutely need hydration to stay alive. They regulate water balance via a process called osmo regulation, which is common to many other vertebrates, including humans. Ultimately, says Kennelly, osmo regulation maintains the appropriate amount of salts and water

in the body, and two main organs facilitate this process. First, the kidneys kick into gear, helping to maintain salt levels, and second, the gills have special cells that exchange water and salt with the environment. Notably, the process varies quite a lot depending on where the fish lives, in freshwater or in salt water. Freshwater fish don't stively drink water because it would dilute their blood and bodily fluids. Kennely said the challenge for a freshwater fish is different than

a marine fish. For fresh water fishes, the blood and tissues are much saltier than the external environment, and thus water follows this osmotic gradient. That is, the body is a salty sponge. So the challenge in this case is to keep water from diluting the body. To counter this, the kidney of a freshwater fish expels a lot of

water from the blood and creates very dilute urine. He noted that freshwater fish are almost always peeing out this diluted urine, while their gills are constantly pumping salts back into the body using these specialized salt cells. On the other hand, saltwater or marine species often drink water through their mouths to keep hydrated. The challenge there is to avoid losing water to the much saltier environment and to

keep excess salt out. And Kennely explained their kidneys remove salt and conserve water, while the salt sells in their sills pump salt into the water. Using these different directions of passing salt and water, the bodies of marine and freshwater fish are equally hydrated and salty. But what about a nadronous fishes like salmon that swim in both freshwater and saltwater. We also spoke via email with Rebecca ash An,

assistant professor of Fisheries biology at East Carolina University. She explained that salmon take the change in stages sort of like an airlock quote an adult salmon migrated into fresh water in order to reproduce. There's often a staging area

where the salmon hang out before completing their migration. This staging area is located so that the fish are exposed to some brackish or fresher water so that they can gradually gain osmotic competency before migrating into their freshwater spotting grounds. As climate change rapidly warms the world's waters, fish like salmon may experience fast changing conditions regarding temperature stability in water columns around the globe. This can dramatically all turn

the way fish adjust to the water's characteristics. Ash says that in some cases where warming causes sea ice to break off and float freely in a salmon staging area, quote, there will not be a lot of mixing between fresh and saltwater because the sea ice produces a large amount of fresh water as it melts, and this serves as

a barrier preventing mixing. In that scenario, this barrier prevents salmon from being exposed to brackish water, which delays their ability to adapt to varying salt content in their environment. If this all sounds fishy to you, it shouldn't our own bodies share similarities with fish, Kennelly said, you can even make the case that we are a type of fish, after all, we descend from them. Thus we have retained many of the same osmo regulatory mechanisms are fishy ancestors

had and modern fishes still use. That doesn't mean you should put your fishy credentials to the test, especially when it comes to saltwater. All animals can ingest a bit of salt water, which is about three point five per and salt by weight, but it won't say your thirst. Instead, you'll get thirstier by the minute as your body uses water to eliminate excess salt from your bloodstream. It's critical that fish use osmosis to regulate salt in their bodies.

Without their sophisticated diffusion processes, saltwater fish would literally shrivel up into slimy raisins and freshwater fish that take on water until they burst. Today's episode was written by Nathan Chandler and produced by Tyler Clang. Brain Stuff is production

of iHeart Radio's has Stuff Works. For more in this and lots of other not so fishy topics, visit our home planet has Stuff works dot com and for more podcast for iHeart Radio, visit the iHeart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.