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Zebrafish are basically aquatic lab rats.
They’re a model organism that scientists use to study everything
from development to disease,
in the carefully controlled environment ofa fish tank.
Now, researchers are also looking into how these small,
stripy minnows see,
and they published a paper about it last week in the journal Current Biology.
This study is the first detailed description of
how vision works in a vertebrate
that has 4 kinds of color photoreceptors,
not a measly 3 like humans.
And they found that,
as babies, these tiny fish have really precise vision that’s
more than meets the eye.
In fact, it’s tailored to the differentparts of their environment.
See, zebrafish are naturally found in clear,slow-moving water in Asia.
They rely on their eyes to find their way around,
hunt, and avoid getting eaten.
And baby zebrafish are like all eyes
their eyeballs make up a quarter of the total volume of their bodies
and contain half of the neurons in their central nervous system.
If our babies had similar proportions,
their eyes would be like grapefruit sized.
This research focused on the retina,
which is in the back of the eyeball
where light-sensitive photoreceptors are found.
There are two main types of photoreceptor cells:
rods detect low levels of light
but don’t really detect color
and cones work better at bright levels of light
but can detect color.
In human retinas, rods and cones are pretty evenly distributed,
except for a region called the fovea
where there are more cones and our vision is a little sharper.
But baby zebrafish retinas are more complicated.
While human retinas have 3 types of cones
one sensitive to red wavelengths of light,
one to green, and one to blue
zebrafish have a fourth that’s sensitive to UV light.
And in their eyes, different photoreceptors are concentrated
where they’re needed most.
Baby zebrafish hang out in shallow water
where death typically comes from above,
whether it’s a heron or other predator silhouettedagainst the bright sky.
So the part of the retina that gets light from above
has more rods,
because they just need to see if anything is coming
not what color it is.
大多数彩色的东西 比如礁石 植物
where light-sensitive photoreceptors are found.
are in front of or below baby zebrafish.
So those areas of the retina have more cones,
尤其对红光 绿光 蓝光敏感
especially the ones sensitive to red, green, and blue light
But the single-celled microorganisms thatbaby zebrafish eat are translucent,
which makes them hard to see with those cones.
Except they do reflect a good amount of UV light.
So the parts of the retina getting light from the strike zone,
which is just a cool term researchers use for the horizon of the fish’s vision,
have more cones sensitive to UV light.,
Basically all these retinal regions chunk up the world,
so different parts of the image
have boosted color or contrast
like Photoshop manipulation of the world in real time.
And this probably plays a big role in helping them survive,
otherwise they wouldn ’ t have evolved to be this way.
When baby zebrafish mature, though,
they grow into their eyes, move into deeper water, and
kind of lose their vision superpowers.
Their retinas change to be more like ours,
where different cones are redistributed in a more even pattern.
But not all fish have good eyesight!
The baby whale fish sounds like a poorly named bathtub toy,
我猜应该是短粗的 可爱的 鲸鱼样的
and I guess it’s kind of stubby and cute and whale-like.
But unlike zebrafish, it lives in muddy rivers
in Central Africa where visibility isn’t so great.
So instead of relying on its eyes, it uses electricity to get around.
And according to new research published
in the journal Current Biology last week,
knowing how these fish use electricity
may give us some insight into some serious human diseases.
Several species of fish use electricity to communicate
and sense what’s nearby, kind of like echolocation.
And to do that,
they have electric organs with specialized cells called electrocytes,
which can generate action potentials likemuscle cells and nerve cells.
Action potentials occur
when ions rapidly cross some membranes and alter the electrical charge and
when a whole bunch of electrocytes do this simultaneously,
they can emit an electrical discharge.
But ions can’t cross the cell membrane just anywhere.
They have to pass through special proteins called ion channels,
which are like carefully controlled doors.
Now, baby whale fish can generate
extremely quick electric pulses
that are only 2 ten thousandths of a second long.
They have to keep it short
so they can stay hidden from catfish,
which can also sense electricity and will totally eat them.
So these researchers wanted to know
how baby whale fish make these extremely short action potentials,
so they took a closer look at the KCNA7 potassium ion channel.
Humans have this same protein in our heart and muscle tissues,
but the baby whale fish has a slightly different version.
The researchers discovered a negatively charged patch of amino acids
in the fish’s ion channel
that makes it more sensitive and able to open more quickly.
Understanding how slight differences in these ion channels affect how they work
might someday help scientists treat diseases like epilepsy,
and certain heart rhythm and muscle disorders.
These conditions are linked with genetic mutations
that also change how potassium ion channels work.
So maybe understanding this odd little fish will help scientists find a fix.
Thanks for watching this fish-filled episode of SciShow News!
If you’d like to stay up to date
on the latest research in all fields of science,
from aquatic vertebrates to human medicine, we post these News episodes every Friday!
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