Thanks to the Monterey Bay Aquarium and their research
and technology partner MBARI for partnering with us on
this episode of SciShow.
They are super excited for folks to learn about the deep sea.
[♪ INTRO] Even though they live in Earth’s largest
habitat, we just don’t know a whole lot about the extraordinary
creatures found in the deep sea.
So we typically have to base our research on animals that
were caught in trawl nets, or more recently, by combing
through thousands of hours of deep-sea video recording.
This means we’re often left with more questions than
answers.
That was certainly the case for a few different taxonomic
families of deep-sea fish that had long been puzzling
scientists, some for over a hundred years.
Despite collecting many individual fish with shared traits
that helped us place them into three distinct groups, some
key specimens from each family were weirdly absent,
leaving huge gaps in our understanding of their lives.
So we thought we knew very little about these three
different families of fish, but as it turned out, we actually
knew a lot about one.
The fish family Cetomimidae has been known to scientists
since as early as 1895.
They’re called whalefish because, well look at them, and
they’re about as unusual-looking as you’d expect a fish
found in the deep sea to be.
They have tiny, poorly developed eyes, but seem to get
along just fine without sophisticated eyesight.
After all, there’s not much detail to see way down
in the midnight zone, the midwater area below 1,000 meters
and the ocean floor.
Instead they’re equipped with large sensory pores that
detect the movement of predators and prey, allowing them
to navigate their surroundings even in complete darkness.
But it’s not just their unexpected appearance that made
scientists puzzle over the whalefish.
Even though researchers have collected more than 600
specimens of several different species from within this
family over a hundred-year span, all of them were female,
and they were always sexually mature.
Without any known males or juveniles, this family
remained a mystery.
Up until the early 2000’s, we were also puzzling over the
Megalomycteridae, a family known as the bignose fishes, also found below 1000 meters.
These fish are long and fairly small, with their namesake
large schnozz.
It houses large nasal organs, presumably to sniff out a mate.
Adding to the curiosities about these unusual fish, adult
males don’t bother to eat.
They have immobile jaws, and no esophagus or stomach, just a big liver
storing energy.
They also have a pair of enlarged gonads, so it would
appear their strategy is to survive just long enough to
reproduce.
And they represented a parallel head-scratcher to the
whalefish.
All bignose specimens were male.
Enter puzzle number three, the Mirapinnidae family, which
are generally found above 200 meters.
These astonishing-looking fish have large mouths with
jaws pointed dramatically upward, like an intense
underbite.
The family is mostly composed of species of tapetails,
which have a long streamer on their tail fin that can be up
to nine times their body length.
That is, this is what they look like as larvae.
Despite having collected over one hundred individuals
since the 1950s, only sexually immature tapetail specimens
were ever found.
Well, put together one fish family of only females with one
family of only males, add in another of only juveniles,
and you get one true family of fish!
Sure, congratulate yourself for calling the twist, but nobody
laid it out that way for the scientists who had to piece it
together!
Thankfully, while looks can be deceiving, DNA doesn’t lie.
In 2003, researchers compared small segments of the
genome called mitochondrial DNA between a juvenile
tapetail and female whalefish.
And their mitochondrial genomes were almost identical.
And not long after, new bignose male specimens were
found together with whalefish females at depths below
1500 meters, which sparked a connection between these
two families.
In 2009, scientists also determined that some of the
bignose males were actually juvenile tapetails, changing
shape as they matured!
They performed further DNA analyses to close the book on
both the bignose and tapetail families, confirming that they
were in fact all one family, now collectively known as
Cetomimidae!
And now that we’ve finally put their story together, we can
better appreciate their unique adaptations through different
stages of their life cycle, and between sexes.
As juveniles, fish in this family gorge on small crustaceans,
thanks to those big vertically-positioned mouths.
But when they mature, they not only travel a thousand
meters or more down into the ocean depths, but their
bodies become radically different depending on their sex.
Species within this fish family showcase an extreme
example of sexual dimorphism, where the males and
females can look dramatically different from one another.
As the males develop into adults, they lose the ability to
eat.
Instead, they store the energy from their last meals in
a giant liver, which they rely on as their sole source of
nutrients for the rest of their lives.
Presumably, this gets them through their search for a mate
and not much longer.
Meanwhile, females continue eating and grow to be much
larger.
Their jaws get longer rather than smaller, which
allows them to gulp up very large prey.
While there’s still a lot to learn about the life strategies of
these fish, these two opposing adaptations would help
both males and females survive in the ocean depths where
food might be hard to come by.
While we’ve cracked the case that puts these three
families together into one, we still haven’t fully matched
together all the different life stages.
We now know there are over 20 individual species of
Cetomimidae, but we won’t fully understand who’s who
when it comes to matching larvae with males and with
females until more genetic analysis is done.
So although we’ve solved one big part of the puzzle, we’re
still far from having a full understanding of these
extraordinary deep-sea fish.
It just goes to show we still have much to learn about
deep-sea inhabitants and the extreme lives they live.
Thanks to the Monterey Bay Aquarium and their research
and technology partner MBARI for partnering with us on
this episode of SciShow.
You can make like a whalefish and swim over to their
websites and social media.
MBARI’s YouTube channel has awesome videos about the deep sea, and on
the Aquarium’s website, you can make a donation
to support their exhibits, education programs, and ocean
conservation work.
Oh, and the Aquarium’s YouTube channel posts these
amazing lofi mixes set to relaxing Aquarium videos that are
perfect for getting work done, if you need somewhere to go
next!
[♪ OUTRO]