before this week if i'd had to name one
thing that separates the not fish from
the fish
it would have been breathing air yes
there are obvious other differences too
like feet but changing the whole system
and animal uses to literally
take in the molecules that keep it alive
feels more important somehow
except in working on this episode i
learned that sometimes some fish breathe
air too
and it turns out there are a lot more of
them that do this than i had originally
thought
for example mudskippers these little
bug-eyed guys actually breathe through
their
skin when they're on land yes i said
fish on land
that is also very weird and how about
the walking catfish
despite the name they don't actually
have feet
but they do have an accessory organ that
lets them breathe air
when they like the mud skippers decide
to just leave the water
and then there's the lungfish which okay
fair enough
they have lungs it's in the name i can't
really be that surprised about that one
what i'm trying to say is
if you're an air breathing fish there
has to be something else weird about you
to make you a bizarre beast
good thing gars have that
today there are seven living species in
the gar family
and they're only found in the americas
from as far
north as southern canada to as far south
as costa rica they mostly live
in warm shallow freshwater habitats like
lakes and rivers
but some species like the alligator gar
which can grow to more than three meters
in length
also venture into brackish and salt
water and where they live
is really important it's what makes
their ability to breathe air
a useful adaptation instead of just a
neat party trick
and it might be partially responsible
for one of the
other strange things about them see you
and i
we're obligate air breathers we don't
have any other way to take in
oxygen but gars are considered
facultative air breathers
they have gills that take in oxygen from
the water they're in
like a normal fish but when that water
is low in oxygen
they can surface to gulp air into a
specialized swim bladder
they have oxygen options and warm
shallow slower moving water tends to
have
less dissolved oxygen in it than cold
fast-moving water
in fact one study found that gars
breathe air more often
when the water they're in is warmer so
gars can survive in places that other
fish
ones that only have gills can't and one
of the things they do
in those lower oxygen places is
reproduce female gars
lay thousands of eggs at a time and the
different species have slightly
different preferences about where they
lay their eggs
for example alligator gar spawn in the
shallow grassy floodplains formed when
rivers flood their banks
long nosegar prefer to lay their eggs in
gravely or weedy places in small
fast-moving streams and florida gar like
weedy backwaters
or a shallow pool but one thing that all
gar eggs or roe
have in common is that they're poisonous
but
only to some animals experiments where
mice and crayfish were fed
garrow went badly for those critters
and the eggs are also toxic to birds and
for humans
no gar caviar for us either thanks
case reports from emergency rooms on
people who have made the mistake of
trying it
promise nausea sweating vomiting and
diarrhea
not fatal but definitely not a good time
to quote my co-host hank green
here don't eat that fish and red eared
turtles though
don't seem to react to the toxin if
they're fed the eggs and the fact that
fish aren't affected
might have to do with the whole gar air
breathing thing
mammals birds and arthropods like
crayfish can potentially hang out in the
kinds of
lower oxygen environments that gar
frequent but other
fish can't so maybe gar
eggs are only poisonous to the kinds of
animals that have been around to
potentially prey on them
or it might just be chance regardless
it's pretty rare
only something like 10 genera of fish
out of over 5200
are known to have poisonous rose as for
what makes the eggs toxic
well researchers seem to only kind of
know it's usually just called an
ichthyotoxin
which means it's a toxin made by fish so
not very specific it seems to be slow
acting and the amount that's consumed
does seem to matter one very weird
experiment that applied alligator
garrote extract
to isolated turtle hearts
suggested that whatever the toxin is it
somehow messes up the ability of cells
to maintain the balance of calcium ions
they need
to function correctly so it looks like
while some turtles can eat the eggs
applying the toxin directly to their
hearts still goes badly for them and no
i have no idea why they tried that
the study actually doesn't say just
don't eat gar eggs
seriously you can eat their meat though
if that's something you're into
if you can get to it you're going to
need something more heavy duty than a
filet knife
because gar scales are basically fishy
armor along with
regular bone those scales are also made
up of a material called ganowin
which seems to be closely evolutionarily
related to tooth enamel you know
the hardest substance in your entire
body guards aren't the only fish with
this kind of scale either the sheers
also have ganoid scales and like gars
they are the living representatives of a
really ancient lineage of fish both
groups
separately split off from the rest of
the family tree of fish
more than 200 million years ago gars
are survivors between the poisonous eggs
and the armored scales
it's kind of no wonder they've stuck
around for as long as they have and what
i think is really funny about this whole
story of a
weird family of fish is that it started
off with the one thing they share in
common with us
the ability to breathe air first off we
want to thank dr
solomon david for pitching us on these
excellent fish
and for all of his help with this
episode if we've made you a fan of gars
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[Music]
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