Listener Questions: Do Fish Smell Fishy to Fish?

In this listener questions episode, I talk about how fish smell smells, whether hyenas grow winter coats, and animals who don't mind spending a lot of time to get the job done, even thousands of years. 

See omnystudio.com/listener for privacy information.

Episode Transcript

Speaker 1 (00:05):
Welcome to Creature Future production of iHeartRadio. I'm your host
of Many Parasites, Katie Golden. I studied psychology and evolutionary biology,
and today on the show, I'm answering your questions. That's right,
your questions about animal behavior, about biology, about sometimes pets. Uh.

(00:25):
You can send me your questions at Creature featurepot at
gmail dot com and I do my best to answer them.
Got some really good questions this time around, so let's
get right into it. Here is the question. I've been
breathing here since shortly after I was born, so maybe

(00:46):
it's hard to think about having gills. We can't smell
anything without drawing air through our nostrils. How to fish smell?
And how do shark smell blood in the water for
miles away? Do they smell with their gills or something?
This is from j T. And I do want to
point out the title of the email because it's very funny.

(01:10):
It is do fish smell fishy to fish? So very
good question, and yes, so fish do smell fishy to
fish in the sense that fish can smell other fish
and other things in the water, So this is a
great question. Smells work a little differently under water. So

(01:35):
up here in the air, molecules are carried by the air.
We inhale them and they go up in our nostrils
and they bind two olfactory receptors in our nasal cavity,
and so that is how we will smell something. The
molecule will lock on, that'll trigger a chain reaction of

(02:00):
neural cells to our brain, and then we identify something
as a smell. And obviously the strength at which we
can detect smells depends on our species. Humans are decent smellers,
We're not amazing. Something like a dog is really really good,

(02:20):
and you can see with a dog they have a
lot of techniques that involve the passage of air in
terms of smelling things. So you see a dog kind
of sniffing the ground and then exhale like snort out.
That doesn't mean that the dog doesn't like the smell.
Means the dog is trying to get a better whiff

(02:42):
of it, with the air going both into the nostril
and then those molecules binding to receptors and then forcing
it back out of the nostrils once again, the air
carrying the molecules passing over these sensitive receptors once again,
and then they have a second pass at picking up

(03:02):
even more molecules, and they have really really sensitive sense
of smell. So all of that is enabled by the
air carrying these molecules. But underwater you can have a
very similar thing happening. So in the water, obviously you
don't have molecules carried by the air. You have them

(03:22):
carried by the water. So fish receive chemical information through
the water. It's a very good hypothesis that there might
be olfactory receptors in their gills, given that the waters
they have to have water pass over those anyway, so
it's a good spot to have some receptors there. In fact,

(03:47):
they do have receptors there. Technically they're not considered olfactory receptors.
They are taste receptors in their gills. In effect, it's
a very similar result where these receptors are picking up
on chemicals in the water, chemicals being any kind of

(04:09):
like compound, any molecule, and are sensing that. It's just
like they're the way that we've mapped sort of the
fish brain. Some we categorize as olfactory receptors and some
as taste receptors, just like in humans. But yeah, taste

(04:29):
and smell are very very much connected, very similar in
terms of how it works in terms of things binding
to receptors. So technically the receptors that they have in
their gills are taste receptors. But they do have noses.
I know it doesn't look like it, but if you

(04:51):
look at a fish or close up, they have nostrils
and those open up to olfactory chambers. Their nostrils, unlike ours,
are only used for smells. They do not breathe through
these nostrils. Their gills they use for breathing, as in,
they take in water and the water flows over these

(05:15):
gill structures that collect oxygen molecules from the water that
the fish can use. The nostrils don't do that. The
nostrils collect water solely for the purpose of smelling it
by the water flowing through, and again they pick up
these molecules, but instead of it being oxygen, they're picking

(05:36):
up any kind of like small molecule that combined to
these olfactory or scent receptors in this nasal cavity. And
then since what that is, so water containing molecules of
things like amino acids or other chemicals enter into this

(05:59):
old factory chamber and bind to the receptors in there.
This exact same thing goes for sharks. So sharks are
a type of fish. They have a similar situation with
their nostrils where the water goes in and carries these
molecules with it and then binds to the olfactory receptors.

(06:23):
So they may pick up on say, amino acid proteins
from blood which flow into their nostrils and bind to
their receptors, allowing them to follow its scent from up
to around a quarter of a mile away. They're very,
very sensitive to this. But it's not true that they

(06:46):
can smell a drop of blood a mile away. The
scent would be too diffuse before reaching them, because you
think about it, the physics of it, the molecules from
that blood droplet have to diffuse use far away enough
that the shark can get, you know, some amount of

(07:07):
the molecules, these little proteins from the blood up in
its nostrils. So if it's too far away, just mechanically speaking,
it's not feasible. But the sensitivity of a nose can
be that it picks up on a very small number
of these molecules, where for maybe other fish or other animals,

(07:29):
it would be way too low of a concentration for
them to pick up on it, but they can smell it.
So like the difference between say, humans and dogs, we
need a higher concentration of these molecules to actually like
have it trigger a response in us, whereas with dogs
they have more receptors, they're able to pick up on
lower concentrations of molecules in the air. So a similar

(07:53):
thing with sharks, who are very sensitive smellers, but not
maybe as much as the sort of internet or old
wives myths have about them being able to like smell
a drop of blood from miles away. So there are
other animals in the ocean aside from bony fish, and

(08:15):
they have different methods of smelling, but it follows the
same principle of picking up molecules from the water that
then bind to receptors. So, for example, sea slugs have
a rhinophores, which are these horn like protrusions that pick
up on chemicals in the water and it binds to
them and it's you know, sort of a form of

(08:36):
taste or form of smell. Octopuses have dimples in their mantles,
so the mantle is the main part of the octopus
and they have these little these little indentations, very very
tiny pores where they can detect smells and you know,
so like the water will flow over their mantle and

(08:58):
it'll pick up on these molecules and they'll bind to
these receptors. Their tentacles have taste receptors to further explore
their environment, so like they have to for their tentacles
to pick up on tastes and stuff like, you know,
it's more of a tactile thing. They can like touch
things and that will help them to pick up on

(09:20):
the taste of an object or the chemicals that are
coming off from it, and then other like all sorts
of different animals have sort of different organs or places
upon which these receptors are, but the mechanics of it

(09:43):
are pretty similar, where it's like a molecule binding to
a receptor. So for example, starfish have olfactory receptors all
over their skin, but it's the same technique where the
water passes over it, molecule binds to a receptor and
then that they perceive that they have the feedback of

(10:05):
like oh, here's something, and they can move towards it
or away from it, depending on what it is so
great question. Yes, fishes can smell, both smell as in
being smelly and smell as in detect odors. Onto the

(10:25):
next listener question. Hi Katie. Recently I've seen a post
circulating online claiming that hyenas can grow a winter coat
when exposed to colder climates. I cannot find proof one
way or another and was hoping you could help me
find some evidence. Thank you for the help, longtime listener

(10:45):
and zookeeper. This is from k Ewart and there is
a Reddit post that they sent as well. And I'm
looking at a fluffy hyena who appears to be sort
of buy some rocks and also buy some snow. So
this is a This is a great question. Always, if

(11:06):
you have there's like some kind of internet claim about
animals and you're sort of curious about it, please do
contact me because I love digging into these things, especially
when it's like something you just see all over and
there's no never like a link to a study or
an article or some experts say anything about it. So

(11:30):
let's investigate this. Do hyenas grow winter coats? A social
media post also makes a claim that that hyenas can
grow winter coats? Because they used to roam Europe. So
first let's let's explore the second claim, because that's that
one's easier to address. We're hyenas ever in Europe. This

(11:51):
part is true. So spotted hyenas, as well as extinct
relatives of hyenas, including the giant cave hyena, did live
in Europe for around a million years, but at about
twenty thousand years ago, their range was forced south. It's
not exactly known why they had to abandon Europe. It

(12:14):
may have been due to the colder climate or having
to compete with humans for resources. It could have been
a combination of these factors. Right, it got colder, harder
to get food, but then they also had to compete.
There's no definitive theory on this that has been sort

(12:36):
of I mean, it's really hard. It's really hard to
prove anything that happened in the past. But the understanding
of why hyenas had to leave Europe is not super
well understood. There's just some theories that lack a whole
lot of evidence. So they did exist in Europe though,

(12:59):
for sure, and they did exist in cold climates before
they were forced to leave, And we don't know whether
they were forced to leave because say, their coats were
insufficient or something like that. So onto the winter coat claim.
So I looked and do this. I saw tons of

(13:21):
posts about this on various social media websites, and like you,
none of them I could find any reliable sources, Like
it would just be this claim like did you know
that hyenas grow winter coats because they used to live
in Europe? And variations of that all over. Very frustrating, right, like,

(13:43):
you know, how do you determine whether this is true?
And I looked on Google scholar which is sort of
my go to resources in terms of really trying to
find some kind of evidence of something. I couldn't actually

(14:03):
find any really good sort of studies on this. The
closest things I found were like kind of vague claims
made by books written I don't know, like in the
nineteen thirties or something, right, So not really I wouldn't
consider that a reliable source, so I'm not going to

(14:26):
use that as one. But I kind of dug into
the posts themselves, these social media posts, and interestingly, I
found that they depict different species of hyenas, So some
of these posts depict like a brown hyena, And if
you a brown hyena is going to be different than

(14:48):
a spotted hyena. They actually have a longer, shaggier coat
than a spotted hyena. But they have this coat year
round and they're they're they're very they're very cute, they
look very nice. But it's like basically claiming that this
is a spotted hyena, right, because spotted hyenas are the

(15:08):
ones that used to be in Europe, and then showing
a brown hyena. So I think part of that is
that it's subverting the expectations of the person, right, like,
who may not know the brown hyena exists because they're
only expecting the lion King's sort of hyenas with the
really short coats and not the brown hyena, which has

(15:32):
a longer coat. So yeah, brown hyenas are a different species.
They have thicker coat year round. They live in Africa.
Their coat could be used for thermal regulation or protection,
but it's not really meant for cold winter seasons. But
including the post that the listener sent me, there are

(15:53):
posts that genuinely depict spotted hyenas with shaggy coats and
the images of actual spotted hyenas In these posts, to me,
actually do show a normal variation in coat and main

(16:14):
and not necessarily one that is seasonal. So one source
of the confusion could be that spotted hyena fur length
changes as they age, So from seven to fifteen months
old they have longer fur, which then gets a bit
shorter as they're older, and then really old hyenas might

(16:35):
have some hair loss that gives them a much shorter coat.
Can also depend on the health of the hyena. If
the hyenas more malnourished, it's not going to be able
to find off mites and parasites as well, so then
it might have more mange or more hair loss, more itchiness,
so then it'll have a thinner coat. And so there

(16:55):
are a lot of factors that can affect coat length
and hyenas. I really couldn't find any evidence any indication
of their coat length changing seasonally with colder weather or
being triggered somehow to grow out, say if they're at

(17:17):
a zoo where there's colder weather than they would encounter
in their natural habitat. Really couldn't find any evidence of that.
That doesn't mean it couldn't be true, right, Like, there
could certainly be some effect that temperature has on their shedding, right,
I think it's completely plausible that if it's cold, somehow

(17:41):
the hyena's hair follical growth cycle could be affected by that, right,
very believable, But couldn't find any studies on it, couldn't
find any evidence. But I did find plenty of evidence
that there are lots of variations in hyena coat length

(18:03):
as well as the patterns on it that does not
have to do with temperature, So that could be basically,
these these posts, like these images could just be say
a younger hyena at a zoo where there's snow around
and someone took a picture, and that are making this
claim that in general hyenas grow out these longer coats

(18:28):
in the winter without any evidence of this being true.
So I'm not going to say it's not true, because
again I think there's a it's a plausible hypothesis that
hyenas could grow out their coats in the winter, but
I couldn't find any evidence of it, And so when

(18:50):
there's no evidence, I think it's not responsible to make
the claim that this is something that is happening, right,
especially knowing that you can have a law kind of
a long haired spotted hyaena uh in perfectly warm weather
like that. If you if you look at like go
online right like, if you're curious and look at images

(19:11):
of spotted hyaenas, you will see uh pictures of them
in Africa in what's probably perfectly warm weather, with a
variety of coat lengths, short, longer. And I would suspect
that a lot of that has to do with age
and health things like that. Yeah, but no evidence. It's

(19:35):
it's temperature based. There could be some effect, but yeah,
we don't know. And this claim that they have this
sort of latent gene or capability to do it because
they used to be in Europe, yeah, I really could.
I couldn't find I could not find evidence of that,
so you know, still could still could be true, but
you can't can't make a claim unless you actually have

(19:58):
evidence of that. So it's you know, social media is
frustrating in that way, really spreading like something that it
could be misinformation, and it's I think what's frustrating about
it is there are plenty of really cool facts about
hyenas and other animals that have plenty of evidence supporting it.

(20:21):
And if this is true, and somehow the first person
who posted it had some access to a study that
was done on this, and then that got lost in
a mix. That's also really frustrating because I can't using
my modest research skills, I'm unable to track it down.
The listener, who I'm sure also has research skills, couldn't

(20:44):
track it down. So then you lose that like if
it ever existed. You lose that connection to actual research,
which is especially important with like social media posts, because
there might be some real research and then you look
into it, maybe the details are a little different right
from what the social media claim is. And yeah, I

(21:05):
mean things are just gonna get worse and worse with AI.
I've seen a lot of posts of animals that are
making some claim about an animal and it's not even
a it's not even a real image of the animal, guys.
It's like it's AI and it's you know, my There's
like this video of a koala quote unquote adopting kittens

(21:29):
and picking them up, and I was looking at it
and my immediate feeling was this is not real. Just
there is something about it that felt a little uncandy,
even though it was very photorealistic and indeed it's a I.
And then when you really looked at it, you could
see that the number of toes and the placement of

(21:49):
the toes on the koala is all wrong. So yeah,
there's gonna be a lot of these claims made online
about things, so please do, like, I really do like
to try to either debunk or bunk these things. I
don't know if bunk is the opposite of dbunk, but yeah, like, uh,

(22:11):
send me if you find something online on social media
where it's like making some claim about animals or even
like an image of an animal that you're like, is
this real or not? Do feel free to send that
to me. You can write to me at Creature Future
Pod at gmail dot com and I'll help you figure
that out. Because I think it's increasingly difficult to parse

(22:32):
media landscape. It's important to be able to do that,
and it's it's getting it's getting harder. It's getting a
lot tougher to uh identify misinformation. And so if it's
something that's like outside of my area of expertise, I'm
not very good at it because like the like AI
and stuff is getting really good at faking faking you out.

(22:56):
So yeah, thank you so much for that question. All right,
on to another listener question. I watched a video recently
about human persistence hunting and the video said the hunt
took eight hours. This make me think, first, are there
other persistent hunters in the wild? And then what is

(23:16):
the longest an animal will take to do a single task?
For clarification on what I mean, what is the longest
amount of time a spider will take to build a
web and doesn't take breaks while building its web? What
about burrowing animals? How long will they take to build
their home? What about mating displays? What is the longest

(23:36):
an animal continues its dance or display before it will stop?
Or are there animals that will dance to their deaths? Thank
you for the wonderful podcast and for helping me understand
evolution a little better, which is to say, now understand
evolution less than I thought, but more than I did.
But that's science. And this is from Daniel Hi. Daniel, Yeah,
I mean, I think when you start learning stuff, you

(23:59):
realize how much you don't understand. So getting more confused
is actually sometimes assign your understanding things better. And I'm
certainly confused a lot of the time. So you are
right in that humans are thought to have hunted not
by necessarily being the fastest or the strongest, but by

(24:19):
being able to out endure or outsmart their prey, so
distance running, tiring out the prey, but also hunting together
and using strategy. We have a pretty unique ability for
patients long term or medium term planning. That doesn't mean
that we are the only ones, though, So let me

(24:43):
I would actually just like to eat with your examples.
Just answer all the questions in your examples. So the
spider web question of like how long you could a
spider take to build a web, it's a really interesting one.
We can both look at individual spiders who build a
web on their own and social spiders who There are

(25:07):
various species of social spiders who usually are these little
tidy spiders who live in these big communal webs. And
so first let's look at individual spiders. A spider who
will build her web all on her own. Many species
of spiders can complete a web in around an hour.

(25:30):
Kind of depends on how big it is, how complex
it is, so anywhere from like twenty minutes to an hour.
It certainly takes some patience, especially because there might be
some interference and they have to start over again. But
for a real marathon weaver. We can take a look

(25:54):
at the Darwin's bark spider. These are little spiders. They're
less than an inch and diameter, cute little fluffy spiders
if you are into that sort of thing. They're found
in Madagascar and they make these giant webs all on
their own, so like where the basic the baseline structure

(26:18):
of the web can be up to twenty five meters
or eighty feet long and then two meters wide, so
they have what's basically like a giant bridge made out
of web, and then kind of in the center of it,
you have this large expanse where it is an actual

(26:39):
like spider web with the spiral and the reticulated structure,
and that one is about two meters wide, which is
still quite big. So the spider will sit on a
tree branch and spray out a line of silk and
let the wind carry it off to another tree. They

(27:01):
like to do this sort of at river banks where
there's like trees on one side and the other side
of the river and you have a lot of insect activity.
So the silk is really strong for it's a diameter,
but it's also really really light, so it might carry

(27:21):
it across the river, and then the wind takes it,
and then it settles on another tree and wants the
spider sense is that it basically has this long line,
like I said, up to like twenty five meters, and
now it can use that as a bridge for building
the central web. So it goes out. It reinforces first

(27:45):
this like sort of tether this line running between the trees,
and then she starts to build the center of the web.
And yeah, it takes a really long time. I wasn't
able to find the exact amount of time that it takes,

(28:08):
but many hours, many many hours to build this. And
she is really really patient because often she has to
restart if some bigger animal messes up the web, or
even if another another spider, either her own species a

(28:29):
Darwin spark spider or some other orb weaver spider finds
the structure that she's building and tries to sort of
steal her foundation to build its own web, and so
she'll have to like fight off this other spider or
cut off the webbing herself, and so she has to

(28:52):
restart and tear it all down. She'll actually collect the
webbing the silk, bundle it up and then she'll eat
it because that's valuable for resources that she can't like
redeploy the webbing, but she can eat it get some
calories so that she can produce more of the silk

(29:15):
from her spinneret, which is an organ on her abdomen.
They create a huge amount of this silk. And it's
not one hundred percent understood exactly how these little spiders
are capable of producing just so much webbing to make
these big, big webs. But they must have a very

(29:38):
efficient metabolism, and as their behavior suggests in eating webbing
that they have to recycle, they must be very very
good in terms of allocating their resources so they can
produce a good amount of silk. So, in terms of
social spiders, this is like a different species of spiders,

(30:00):
the little ones that live in these big, big communal groups.
There's many different species of these, and because they work
in large groups, these they're more human like in their
ability to create structures that take multiple generations to finish,

(30:22):
sort of like humans building a cathedral, right, So they
create these multi generational webs that take long beyond a
spider's single lifetime to build. And so recently there was
actually a social spider web found that's over one hundred
square meters found in a cave between Albania and Greece,

(30:45):
made by over one hundred thousand tiny spiders. And this
has probably taken many, many, many, many many many generations
of these spiders years and years to build this up.
I don't think they know yet. This is a relatively
recent discovery. They don't know yet how old it is.

(31:07):
I would not be surprised if it was, you know,
over one hundred years old. And when it comes to burrows,
we can actually turn to another arthropod. So termites definitely
when the prize, when it comes to patients and building burrows.
They build these giant tunnel systems that can sometimes be

(31:31):
built over thousands or tens of thousands of years. So
these are termites building tunnel systems and termite mounds, which
the mounds are basically like the dirt that they have
to extract from the ground in order to excavate these
massive tunnel systems. And so they may have built started

(31:56):
these structures tens of thousands of years ago and are
still being inhabited by living termite colonies to this day.
In Brazil, there is a termite colony estimated to be
around four thousand years old. It is the size of
Great Britain. So in it's this large area with two

(32:21):
hundred million termite mounds, which you know they're not always
like big mounds, but you know there is it is,
there is a mound there of some of this dirt
that has been excavated and put above ground. It is.
I didn't really when I saw these these numbers, I

(32:44):
was like, no, this is it has to be misinformation.
I looked into it, and it seems to be genuine
that it is just genuinely a termite country. That it
is that these termines have over thousands of years built
up in this Brazilian Uh, these Brazilians plane planes area.

(33:08):
So the termites created what's essentially like an entire England
size termite civilization. Yeah, let's let's keep going on with
these really patient animals. The question asker really did identify
an area in which animals have to be typically quite patient,
and that is courtship rituals. That's usually an exercise and

(33:33):
endurance and patients which might help the female select a
male who has the fortitude UH to provide good genes.
For example, for a lot of species that do co parenting,
the assessment is often like, hey, can this other this

(33:56):
this mate like actually have the attention span, the devotion
and to be able to take care of our offspring together.
So let's talk about some of the interesting mating rituals
that take a long time. So, the greater mouse eared bat,

(34:16):
which is the largest native bat in Europe, compete for
females in les so alek is a mating display arena.
It's a word used for multiple in any kind of
species that uses like this, like basically a big mating
area grounds and competes for female's attentions there. So these

(34:40):
mouse eared bats will find a bit of roosting territory
and they will defend it from other males and let
out these trill vocalizations to attract the females. So all
of this is tiring enough, but once a female actually
comes and chooses him, mating can last over thirty hours.

(35:02):
That's three zero thirty hours of mating. So this doesn't
mean they're kind of constantly having sex during this time.
A lot of it is cuddling actually, so the male
will wrap his wings around the female for hours after
copulation before going at it again. It's very, very time

(35:23):
consuming to do this, very romantic, and it also helps
him reaffirm the bond with the female, so the female
is motivated to stay and also to keep fend away
other males who may try to get in on this mating.
So who knows, maybe human cuddling has you know, there

(35:49):
may have been some point at which human cuddling had
a similar purpose. Right, So, in terms of your other question,
are there any mating rituals where the animal just basely
does courtship until they die. It's not exactly courtship, but
there is an animal that mates to its death, so

(36:10):
this is the antikiness. These are small mouse like marsupials
in Australia who go on frantic mating sprees until the
male dies of stress. So for two to three weeks
they mate near constantly, sometimes a single copulation lasting over
ten hours, which is yeah, there's a lot. The huge

(36:36):
surges of cortisol and testosterone actually kills off their organs
and they die and the females will mourn them by
eating their corpses, which is fuel for the offspring that
the males worked so hard to fertilize. So you know,
your basic meat cute in nature. Well, guys, thank you

(36:58):
so much for the question. If you've got some for
me that you want me to answer on the air
or in a response to your email, you can write
to me at Creature feature Pod at gmail dot com.
That's Creature feature Pod at gmail dot com. Thank you,
guys so much for listening, and thanks to the space

(37:20):
Cosaics for their super duper awesome song XO Lumina. Creature
features a production of iHeartRadio. For more podcasts like and
When You Just Heard, visit the iHeartRadio app Apple Podcasts
or Hey, guess what for you listen to your favorite shows.
I don't judge you, I'm not your mother, but man,
you know make maybe take some breaks when you're doing

(37:41):
a mating marathon. Maybe get a massage or do some
light meditation. Don't be like the anti Guayanas. All right,
see you next Wednesday.