[theme music]
The fishes is the most diverse group of vertebrates on the planet.
With over 33,000 living species,
sometimes it can be a bit confusing and often surprising
as to what constitutes as a fish.
So what exactly is a fish? And why should we care?
If I showed you these ten generally well-known animals,
would you be able to differentiate the fishes from the non-fishes?
Here—take a closer look. Pause the video if you need some time.
I’ll even help you out and put down their most commonly used names.
How do you think you did? Well, stick around.
By the end of this video we’ll most assuredly have a better idea of what a fish is
and I’ll reveal which of these ten animals are fishes.
[Koaw theme music]
Now I bet you already have a good idea of what a fish is.
I bet many of us when we first hear the word ‘fish’ or ‘fishes’
immediately think of our favorite water-themed animated movie
like The Little Mermaid or Finding Nemo.
And others may think of those vibrantly colored creatures
gracefully mingling over coral reefs and within tall kelp forests.
Others may immediately think of the sport of fishing.
Or perhaps commercial fishing and aquaculture.
Or perhaps some of us just think of food.
And fishes come in all shapes, sizes and colors.
After hundreds of millions of years of evolution,
and with extraordinary array of adaptations,
the fishes have figured out how to essentially colonize the entire planet,
populating both hemispheres in the deepest parts of the oceans
and in hypersaline seas
and in land-bound lakes and ephemeral ponds
to raging rivers and mountain streams.
They even live in underground caves
and hidden oases in arid deserts.
And also under the freezing Arctic ices.
Through the millennia, the fishes have greatly influenced
the lives of humanity within industry, culture and religion,
and within every spiritual and intellectual crevice in-between.
And that holds true, even now on this day.
Many populations of humans are directly dependent on the oceans and fishes
as a way of life
as most humanity lives within sixty miles of a major body of water.
With so much biodiversity on our blue planet,
often it can be difficult to distinguish as to what classifies as what
within the animal kingdom, especially within the waters—
a habitat that still offers a vast amount of scientific uncertainties and awaiting discoveries.
There are still thousands of fishes left undiscovered in our world—
now that’s pretty nifty.
We’re going to take a closer look as to what makes a fish…a fish.
Hello everyone, Koaw here.
This is the first video in a mini educational web series devoted towards two passions of mine
—science and fishes. Better said—ichthyology,
or a branch of zoology that deals with the biology of fishes.
Now I know that not everyone is as enthused about fishes as I.
Well…perhaps this little girl is.
And for many, the thought of a mucus-covered fish makes them squirm.
Or the thought of a big shark in murky waters gives them the heebie jeebies.
But I do most all of us are intrigued, if not fascinated by the animal kingdom
and have an appreciation of the splendiferous beauty
and mesmerizing complexity that is nature.
So this web series is devoted towards teaching the basics about fishes,
and then some, for a general audience of all ages
with an intention to be easy to follow, enjoyable, but most of all, a bit educational.
So without further ado, let’s get into it.
So what is a fish?
Yeah, that’s a fish.
Well like most endeavors within the sciences—
from systematics to definitions to theories—
not all scientists and researchers are always in agreement,
which, is actually the imperative driving force behind scientific progression.
We build and expand on the wisdom and knowledge of our ancestors.
And without the criticisms and consensuses of our peers within the scientific community,
we’d still be thinking that the world is the center of the universe
and that alchemy is the grandest form of chemistry.
And the definition of a fish is no different
as it has been dynamically changing since it was first described.
You would be hard-pressed to find matching definitions of a fish
in differing ichthyology texts.
I’m going to take you to a definition of a fish
that I had first learned in my first ichthyology course years ago.
A fish is an aquatic vertebrate with gills throughout life,
and limbs, if any, in the shape of fins.
Now that’s not a bad definition at all—I like Nelson’s definition.
But I’m going to put an asterisk right next to it and I’ll explain why later.
First, let’s break down that definition so it’ll be easier to understand.
‘Aquatic’ – okay, well, that’s an easy one.
What do we think of when we hear the word ‘aquatic’?
Water. Exactly.
That just means that the animals are predominately growing in or living in water.
‘Vertebrate’ –now that’s a bit more esoteric
but that basically means having vertebrae or a backbone, or spinal column,
that provides support to the body and protects the spinal cord or notochord.
Now, to get a bit more technical,
when we’re referring to vertebrates,
we’re referring to all animals within the phylum: Chordata, subphylum: Vertebrata.
Now, you are already quite familiar with the vertebrates,
considering that you are one.
If you ever had a pet dog or cat or turtle or bird, well, those are vertebrates too.
The described living vertebrates,
fishes, amphibians, reptiles, birds and mammals,
make up less than 5% of all known living animal species.
The rest are invertebrates without a backbone.
The fishes are a paraphyletic group
meaning that it’s a group with its last common ancestor
and all descendants of that ancestor
with the exception of one or two monophyletic groups.
Where in this case, the tetrapods,
which are the amphibians, reptiles, birds and mammals, are not included.
I know that’s a bit confusing unless you’re a biology major, so let me show you.
So around 520 million years ago the vertebrates came into existence.
Soon we saw the jawless fishes emerge, the agnathans,
which are represented now by orders Myxiniformes, or the hagfishes,
and the Petromyzontiformes, or the lampreys.
Then the jawed vertebrates, or gnathostomes
came to be in the Ordovician, somewhere around 450 million years ago.
The gnathostomes, now represented by living groups of Chondrichthyes,
or cartilaginous fishes, better known as sharks, skates, rays and ratfishes, or chimaeras,
and Euteleostomi, or the bony vertebrates.
From there, fast-forward 30 million years to about 420 million years ago.
The first actinopterygians, or ray-finned fishes, made their presence known on Earth.
Now representing 96% of living species of fishes.
We’re talking tuna, piranha, tetras, cichlids, salmonids,
well over 30,000 species of fishes.
And the other bony vertebrates mentioned here, sarcopterygians,
showing up about 418 million years ago,
now represented by only 8 living species of fishes:
2 coelacanths and 6 lungfishes.
But the sarcopterygians would arguably progress to be
the most successful animals on Earth via the tetrapods.
And around 390 million years ago, that’s when the tetrapods started to appear.
There are a few fossils of an ancient fish called Tiktaalik roseae,
that is an absolute ideal representation of how the fishes made the transition into terrestrial tetrapods,
that is, how vertebrates evolved to live on land.
And even though Tiktaalik may not be the direct ancestor of modern day tetrapods,
this magnificent fish, or fishapod, as it is often called,
has been a revolutionary discovery of great magnitude.
So again, the fishes are a paraphyletic group of vertebrates.
And so often when we refer to the actinopterygians, or ray-finned fishes,
and sarcopterygians, or lobe-finned fishes,
ichthyologists like to refer to them as the group Osteichthyes, or bony fishes,
replacing Euteleostomi, bony vertebrates,
that is after we exclude the monophyletic group of Tetrpoda.
But in truth, you and I, well we’re Osteichthyan.
We are bony fish.
So is this dude. And this dude. And this dude.
As of now, Dipnoi, or the lungfishes,
are the closest living relatives to tetrapods, or us.
Okay, take a breath.
It’s a lot less technical from here on out.
Let’s go back to our definition—what have we covered?
Aquatic—lives in water. And vertebrate—has a spinal column.
Good. What’s next?
‘Gills’ – gills are just respiratory organs
that extract dissolved oxygen from water,
excreting carbon dioxide as a byproduct.
And lastly we have ‘fins’.
Well, that’s just an attached appendage to the body,
except the fishes, such as the bony fishes,
have rays and spines covered in skin in a webbed-fashion,
and the cartilaginous fishes, well their fins look more like paddles or flippers.
So remember that asterisk I threw up on the definition? Well, let me explain why.
Aquatic—well not all fishes spend the entirety of their time in water.
Some fishes, such as lungfishes,
are capable of spending up to four years burrowed in the ground, or aestivating,
during periods of drought or low water.
Mudskippers are capable of leaving the water during low tide in search of food or mates.
The snakeheads are capable of walking on land from water source to water source.
And the second part of our definition:
well let’s go to vertebrates.
It’s been an up-and-down sort of disagreement-agreement
when it comes to lampreys and hagfishes within ichthyology and systematics.
And figuring out who belongs as a fish and who doesn’t.
Overall, as of now,
hagfishes and lampreys are inclusive in fishes
even though hagfishes don’t necessarily have a vertebral column.
But this is thought to be a secondary loss, or reverse evolution.
Now that just means that ancestor possessed the trait and it was lost over time.
And the third part of our definition—gills.
Well let’s go back to our lungfishes.
All lungfishes except for the Australian lungfish are obligate air breathers
meaning that they have to use their lungs to breathe atmospheric oxygen—
not dissolved oxygen in water—
because their gills are so atrophied in adulthood.
Now we have lungs, and the lungs of lungfishes are homologous to what we have—
meaning that if you followed the course of time their lungs were our lungs.
And there are many other species of fishes that have lungs or modified swim bladders
or some different anatomical feature
where they’re not entirely using gills in order to
incorporate oxygen into their respiratory system.
Those betas that you see in pet stores,
or Asian fighting fish as sometimes they are called, well—
they’re capable of sitting in those jars, looking all sad,
without any aeration because they’re capable of going up to the surface and gulping air.
Fins and limbs.
Well, not all fishes have limbs
and definitely not fins in the way that we may think of them.
The hagfishes, lampreys and many eels,
well they really only have a modified caudal fin for locomotion.
Overall, a definition for a fish that I find to be more befitting
comes from Hastings, Walker, and Galland.
Fishes usually live in water,
usually obtain oxygen through gills,
are usually ectothermic (i.e. cold blooded),
and usually have limbs in the form of fins.
Can you see why I like that definition?
With the quadruple plugging of the word ‘usually’
it simple accounts for all the anomalies of extreme variance within the fishes.
For reiteration, there are a lot of extant species of fishes on the planet.
And when I say ‘extant’, or (ex-tent),
I’m simply referring to ‘in existence,’
which is a word meaning roughly the opposite of ‘extinct’.
Now there is an estimated 82 orders of fishes
and over 500 families
and over 33,000 species of fishes.
And those are only the ones we know about.
There are still thousands left undiscovered.
Now I’m going to put this into perspective for you.
Not only are there more fishes than the amphibians—
more fishes than the reptiles—
more fishes than the birds—and more fishes than the mammals—
there are fishes than all four of those other groups combined.
So why should we care what the fishes are? ♪♪
Well, besides any ethical obligations we owe to them,
and their sheer awesomeness,
humanity is quite dependent on the fishes.
Yeah, I’m serious.
And our first steps toward understanding our relationship to the fishes
is understanding what fishes are.
I salute anyone, from marine biologists to conservationists to volunteers
that are working to preserve and understand fishes and all of wildlife.
As a global society we know that overfishing is bad,
and pollution is bad, and global warming is bad.
But we still have corporations and nations tirelessly working against nature,
eliminating precious habitats such as coral reefs and eradicating irreplaceable species.
All the while completely disrupting vital ecosystems that we too are dependent upon.
We are living in a mass extinction event.
Yes, what killed the dinosaurs was called a mass extinction event.
I’m not exaggerating here.
There are species going extinct every single day.
The best way to help, whether you are 7 or 70, is to embrace the truth.
Learn about fishes. Learn about the ocean.
Learn about your connection to the world’s waters and nature.
Truth is the ambrosia of progression, albeit at times it can be rather bitter.
To sum it up: A fish is usually going to be found in water,
usually going to have fins, usually going to have gills,
and usually going to be ectothermic.
But there are exceptions to all of those rules.
Watch more of my videos. Learn more about fishes.
I’ll catch y’all later.
Okay, I’m going to reveal which ones are fishes on this board.
And if you want a more detailed explanation,
watch my other video where I’ll go over each one.
[theme music] Thanks for watching!