- There are all kinds of fish with blue colors right?
Blue tangs, blue spotted angelfish, starcki damsel fish,
even fish like the potter's angelfish or
the mandarin goby's have some blue in them.
But, are these fish actually blue?
Well, it depends on how exactly you define blue.
Hi guys and girls.
I'm ReefMan and this video is all about how fish
and other plants and animals get their color.
Specifically, blue color.
Blue is a special case amongst animals.
There really aren't that many blue things in nature.
Try to think of a blue flower.
And certainly, if you're really looking for a blue pigment,
it's even more rare.
In fact, of all the fish that we know about,
only the blue mandarin goby,
also called the red or the green
or the psychedelic mandarin, makes a blue pigment.
That's not to say that there's no other species in the ocean
that make blue pigment.
But no other fish that we know of, can do it
So, what about all the other blue things
that you're thinking of.
What about the fish I mentioned at the start of this video?
The blue-ringed octopus, these things are blue right?
Well, all of those things are using trickery and reflection
to appear blue.
This is something called structural color.
Rather than a pigment-based color.
First, it'll be helpful to know that white light,
like what I'm filming this video under
and what you're watching the video under,
is actually a mix of all different colors.
And, that color of light is really dependent
on the wavelength, that the light actually is.
That's what sets it's color.
A pigment is simply a chemical that absorbs
some wavelengths and only reflects certain wavelengths.
So, you know, white light come in,
red light comes out, red pigment.
Because only some of the wavelengths are reflected back
off the pigment, we can see those colors directly,
without the other colors mixed in,
which were absorbed by the pigment.
And a pigment-based color is gonna be the same color,
no matter what light you look at it in or what angle
you look at it from.
Structural color on the other hand, is created by the
interaction of microscopic structures
that change the light being reflected back to us.
These tiny little grooves or sometimes layers,
interfere with the light as it's being reflected
and they cause that interference and a whole different
color to show up.
Because the wavelength actually gets shifted.
And, peacock feathers like this one,
well, they're actually brown,
although you're seeing a lot of color, right?
They've actually got melanin in them, just like our skin
and because of the microscopic structure that is in them,
the interference causes them to appear blue, green
and all those other colors that we see in between them.
These structures are tiny.
There could be only tens or a couple 100 nanometers in size.
And a nanometers is a billionth of a meter.
That's super tiny.
In fact, these structures are tiny enough to interact with
and change the wavelength of light itself.
The distance from one peak to another,
defines the wavelength and therefore the color of the light.
In the case of blue light, that's gonna be around
490 to 450 nanometers between those peaks in the wave.
So, the exact placement of these tiny structures
is going to decide the final color that we see.
And depending on their spacing, we might see red,
green, blue or in the case of iridescent things,
the final color you might see, could just depend on the
angle that you're looking at it from
and what getting reflected from it at that point.
This is why a lot of blue fish appear iridescent.
The mechanism behind the iridescence is very closely related
to the one that produces just structural color in general.
Although, for iridescence there's multiple layers of it.
In this case though, it's almost always these like,
semi-transparent layers of cells that are going to reflect
different lights back up, from both the top of them
and sometimes also the bottom layer.
And that causes the reflective light to be just out of sync.
And when the physics and the interference in these
wavelengths line up just right,
you'll see an iridescent flash of color.
You can see the structure that I'm talking about
very well in this photo of mother of pearl.
That's just the inside layer found in some mollusc shells.
See how there's all these tiny little layers?
Well each of these layers in mother of pearl,
reflects back some light from both it's top and bottom
and because there's so many layers,
we see that shimmering iridescent color,
instead of whatever the boring brownish cream color
the shell would otherwise be.
Lots of fish and other animals do similar things.
and even some minerals, like opal do.
Although, maybe without so many layers.
I thought it was really crazy, that there's only one
blue fish that has blue pigment.
Who would have guessed?
I couldn't believe it.
We have so many fish that look blue,
but it's all just tricks.
It's all just structural color.
Nature is incredible.
I hope you enjoyed this brief intro to color in nature
and in our reef fish.
Like any scientific topic, there is so much more detail
that you can get into with color, wavelengths,
interaction between wavelengths, so dive in.
You never know when you're gonna learn something amazing.
And you know, science like this could just blow your mind.
Until then, enjoy the world around you.
Be kind to each other.
Stay safe.
Don't forget to subscribe.
And have an amazing day.
Bye.