Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey
Speaker 1: brain Stuff, Lauren vocal Bomb here with today's question, do
Speaker 1: fish get thirsty? And? Okay, the short answer is that
Speaker 1: we have no idea because thirsty is a human experience
Speaker 1: of wanting a drink, and any ichthyologist would tell you
Speaker 1: that we can't know what fish or any other non
Speaker 1: human animals are thinking and feeling. You know, exactly when
Speaker 1: you're thirsty, you might experience a range of symptoms, perhaps
Speaker 1: dry mouth, fatigue, reduced to your an output, lightheadedness, and weakness,
Speaker 1: among others. And when you're really really thirsty, like lost
Speaker 1: in the desert without a canteen type of thirsty, you
Speaker 1: simply crave water, sometimes to a degree that you can
Speaker 1: hardly think about anything else. That powerful urge is what
Speaker 1: keeps our bodies from becoming dangerously dehydrated. But because we
Speaker 1: can't put ourselves in a fish's shoes or fins, there's
Speaker 1: no way for us to know how fish perceive thirst
Speaker 1: or if they do it all. But we spoke via
Speaker 1: email with Boston College Assistant biology professor Christopher Kennelly. He said,
Speaker 1: I think of first as a cognitive response to hydration,
Speaker 1: and it's hard to get inside of fish's brain. However,
Speaker 1: we do know quite a bit about how fishes regulate
Speaker 1: water balance. Regardless of their thirst, drive or black thereof,
Speaker 1: these creatures absolutely need hydration to stay alive. They regulate
Speaker 1: water balance via a process called osmo regulation, which is
Speaker 1: common to many other vertebrates, including humans. Ultimately, says Kennelly,
Speaker 1: osmo regulation maintains the appropriate amount of salts and water
Speaker 1: in the body, and two main organs facilitate this process. First,
Speaker 1: the kidneys kick into gear, helping to maintain salt levels,
Speaker 1: and second, the gills have special cells that exchange water
Speaker 1: and salt with the environment. Notably, the process varies quite
Speaker 1: a lot depending on where the fish lives, in freshwater
Speaker 1: or in salt water. Freshwater fish don't stively drink water
Speaker 1: because it would dilute their blood and bodily fluids. Kennely
Speaker 1: said the challenge for a freshwater fish is different than
Speaker 1: a marine fish. For fresh water fishes, the blood and
Speaker 1: tissues are much saltier than the external environment, and thus
Speaker 1: water follows this osmotic gradient. That is, the body is
Speaker 1: a salty sponge. So the challenge in this case is
Speaker 1: to keep water from diluting the body. To counter this,
Speaker 1: the kidney of a freshwater fish expels a lot of
Speaker 1: water from the blood and creates very dilute urine. He
Speaker 1: noted that freshwater fish are almost always peeing out this
Speaker 1: diluted urine, while their gills are constantly pumping salts back
Speaker 1: into the body using these specialized salt cells. On the
Speaker 1: other hand, saltwater or marine species often drink water through
Speaker 1: their mouths to keep hydrated. The challenge there is to
Speaker 1: avoid losing water to the much saltier environment and to
Speaker 1: keep excess salt out. And Kennely explained their kidneys remove
Speaker 1: salt and conserve water, while the salt sells in their
Speaker 1: sills pump salt into the water. Using these different directions
Speaker 1: of passing salt and water, the bodies of marine and
Speaker 1: freshwater fish are equally hydrated and salty. But what about
Speaker 1: a nadronous fishes like salmon that swim in both freshwater
Speaker 1: and saltwater. We also spoke via email with Rebecca ash An,
Speaker 1: assistant professor of Fisheries biology at East Carolina University. She
Speaker 1: explained that salmon take the change in stages sort of
Speaker 1: like an airlock quote an adult salmon migrated into fresh
Speaker 1: water in order to reproduce. There's often a staging area
Speaker 1: where the salmon hang out before completing their migration. This
Speaker 1: staging area is located so that the fish are exposed
Speaker 1: to some brackish or fresher water so that they can
Speaker 1: gradually gain osmotic competency before migrating into their freshwater spotting grounds.
Speaker 1: As climate change rapidly warms the world's waters, fish like
Speaker 1: salmon may experience fast changing conditions regarding temperature stability in
Speaker 1: water columns around the globe. This can dramatically all turn
Speaker 1: the way fish adjust to the water's characteristics. Ash says
Speaker 1: that in some cases where warming causes sea ice to
Speaker 1: break off and float freely in a salmon staging area, quote,
Speaker 1: there will not be a lot of mixing between fresh
Speaker 1: and saltwater because the sea ice produces a large amount
Speaker 1: of fresh water as it melts, and this serves as
Speaker 1: a barrier preventing mixing. In that scenario, this barrier prevents
Speaker 1: salmon from being exposed to brackish water, which delays their
Speaker 1: ability to adapt to varying salt content in their environment.
Speaker 1: If this all sounds fishy to you, it shouldn't our
Speaker 1: own bodies share similarities with fish, Kennelly said, you can
Speaker 1: even make the case that we are a type of fish,
Speaker 1: after all, we descend from them. Thus we have retained
Speaker 1: many of the same osmo regulatory mechanisms are fishy ancestors
Speaker 1: had and modern fishes still use. That doesn't mean you
Speaker 1: should put your fishy credentials to the test, especially when
Speaker 1: it comes to saltwater. All animals can ingest a bit
Speaker 1: of salt water, which is about three point five per
Speaker 1: and salt by weight, but it won't say your thirst. Instead,
Speaker 1: you'll get thirstier by the minute as your body uses
Speaker 1: water to eliminate excess salt from your bloodstream. It's critical
Speaker 1: that fish use osmosis to regulate salt in their bodies.
Speaker 1: Without their sophisticated diffusion processes, saltwater fish would literally shrivel
Speaker 1: up into slimy raisins and freshwater fish that take on
Speaker 1: water until they burst. Today's episode was written by Nathan
Speaker 1: Chandler and produced by Tyler Clang. Brain Stuff is production
Speaker 1: of iHeart Radio's has Stuff Works. For more in this
Speaker 1: and lots of other not so fishy topics, visit our
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