Best Perch Dissection: Part I – External (Jr. High, High School and College Review)

Best Perch Dissection: Part I – External (Jr. High, High School and College Review)

August 19, 2019 0 By Stanley Isaacs


(upbeat music playing) – Hello, I’m Steven Rokusek with South Dakota Public Broadcasting. – And I’m Dale Droge, Professor of Biology at Dakota State University. – And today we’re gonna dissect the … – Yellow perch. – Yellow perch? – Yeah. Yellow perch
belong to a group of fishes called the “ray finned fishes”. You can see that here with
the rays in their fins. They’re interesting
because they’re the largest group of vertebrates –
there’s more than 20,000 species of these, which
is nearly three times the next largest group of vertebrates. Sometimes we don’t appreciate that, because we don’t see them
so much cause they live in the water, but they’re
a very diverse group. But if you think of all
the coral reef fish, and other kinds of deep
fish, or fish that live deep in the ocean, there’s
a large number of these. – Then why select the yellow perch? – The yellow perch for study is probably – it’s easily obtainable,
it’s relatively cheap, it’s a good size, the numbers are good, their
abundance in nature is good so we don’t impact their populations. – And on feeling this before there, there’s definitely some spikes here, as far as, compare this to a shark… – Yeah, a shark will
have more fleshy fins, and something like a catfish,
for example, or a minnow, have more soft rays, their
fins would bend around. A lot of these fish, like
these, a lot of the sportfish, bass, these type of things,
with the ray-finned fish, they have these hard spines
in many of their fins. – And as far as number of fins,
or certain number of fins? – Yeah, yeah. – I can hold him here for you. – Externally, it’s pretty simple. The fins are the dorsal fin,
which we’re familiar with like for sharks, on the back, and in the case of
something like a walleye, it actually consists of
two parts, but it is a single fin that just has two sections. And then we have the caudal
fin, which is the tail. A lot of the pull, or force
for movement comes from the caudal fin pushing against the water. And then the anal fin, which
is down here near the Cloaca, where the wastes come out,
and then in many of the more what we consider “advanced fishes”, the pectoral fins appear in the front, are raised up toward
the middle of the body, and now the pelvic fins move forward. So you have what’s called
the advanced greyfin fish fin arrangement, which is to
have the pelvic and pectoral fins fairly close together. There seems to be an
advantage in maneuverability when they’re floating in the water, then they can turn more easily with that. – Now a kind like this, is it speed, would these help with, as far
as catching prey or anything? – I would probably say maneuverability. The speed would mostly
come from the tail itself. – As far as catching food then, is there any special
adaptations for that then? – Yeah, and in here as we
can see in the mouth here, in the mouth, you can
see it’s a large mouth. One thing that’s interesting
about these kinds of fish is that you think about trying
to capture something in water, if you try to grab it, how the water pushes it away from you. So what these fish actually do
when they get up toward prey, if I could try to pull this down here, you can see the mouth
extends out to large gape, and what that does is
create a suction pressure, and actually pulls small
prey into their mouth. They do this so fast
you almost can’t see it without a slow-motion camera. So it’d come up, and so
instead of grabbing things, instead more or less
sucks them into its mouth. – So then he’d take it in whole, or is there any kind of chewing? – Yeah, not much chewing in fish. They pretty much just swallow it whole. – And then as far as a complete system, is there an anus then,
or how does that work? – Yeah, it’s a little different in fish. If you wanna hold it there, the mouth, of course, comes in, the food goes through the digestive tract, and then there’s the anus
would be right inside of this opening, and so there’s
actually this hole here, this space here, is the
common opening of both the reproductive tract and
the digestive tract. That’s called the Cloaca,
which is Latin for “sewer”, which makes sense when you think about it. They have a single opening
for those two systems. So really, it’s only mammals
that really have separate openings to the urinary system
and the digestive system. – As you were opening that mouth, any kind of nostril up here, anything… – Yep, and we did forget that too. Yeah, there are a pair of nostrils, and they blend in pretty well but they’re right up here, and here. And
they do not go into the throat. They’re there for chemo
sensory purposes, like tasting, or smelling if you wanna think
of that, smelling the water. They’re sensitive to
chemicals in the water. – So, pretty advanced nervous system then? – Yeah, and they have a
fairly large brain under here, all things considered, I
mean compared to a mammal, maybe not that great, but
compared to many other animals, they have a very large brain
protected by a bony brain case and are capable of fairly
sophisticated behavior. – Any other specialized structures
as far as nervous system? – Oh yes, along here,
this is unique to fish. No other vertebrate has this. There’s a line right along here, it’s called the Lateral Line,
and you can see it running, it’s just a little bit
different color as it runs down the mid part of the body. That is a very specialized structure for sensing pressure changes.
Waves hitting up against it, something moving over
here would create waves, that the Lateral Line would sense. So they would know there’d be
some object to the one side and so it’s a sensory system
that only works well in water. – I noticed here, as far as
sights, there’s large eyes? – They have large eyes, good vision, they depend a lot on vision,
and like most vertebrates they have paired sense
organs, paired nostrils, paired eyes, paired lateral lines, so they can tell which
direction sensory information is coming from and respond accordingly. – You’d mentioned it’s
kind of a closed system, as far as there’s no, in the lungs, there’s no type of – no
lungs, I guess… (laughs) – No lungs, there’s gills. (laughs) They don’t need, cause there’s
so much water coming in, they don’t really need that
connection to the throat. – But then how does, as
far as breathing and stuff? – Oh, yup, and one other
structure we should probably look at here is this Operculum. It’s an important
ray-finned fish structure. It’s a bony flap that covers the gills. – Should I kinda pull it
back from the side there? – Yeah, pull it back, that way we can look at the gills here a little bit. – Okay. – I’ll get my finger under there. Yeah, so you can see the
gills lie under there. And that’s a really strong bony flap, and it protects the gills and
it also works in breathing because fish have a system
where they pull water into their throat, and they
push it then, over this way, and at the same time the
gills open up like this, that suck water across. So
basically, these fish are pumping water over their gills. And that allows them to
get oxygen to their tissues even if the fish isn’t moving very much. And that’s unlike sharks,
which have to swim with their mouth open to
push water over their gills. – Interesting. – Yeah, so that Operculum is
only found in these bony fish and is a pretty important
evolutionary adaptation. – Also, right behind here,
all these little scales and stuff, is that… – Yeah, and then another thing, you can – some of these you can
almost flick them off here. Here’s one… you can flick off, so these scales are very, very thin, almost transparent, but
they are made of bone. They’re a very thin type of
bone, that’s thinned down. And they actually lie underneath the skin, so there’s a very thin
layer of epidermis that lies over the top of those bony scales. But over time, some of
the earlier fish like gars and things like that have
these big heavy scales. These ray-finned fish,
many of them have these lighter scales that then
allow them to be more buoyant, and more maneuverable in the water. So they sacrifice protection for weight. – Sure. You mentioned they’re buoyant, something we’re looking for right away? – Yeah, they have a swim bladder inside, and so we’ll take a look
at that in just a second. – Anything else before we
start cutting into it, or…? – I don’t think so, it’s
mostly external anatomy. You can see they have a
basic, what’s called fusiform, or streamlined shape for
moving through the water pretty easily, the tail
pushes side to side and provides that motion.
They’re swimming machines. They’re very well-adapted for
pushing through the water, and with the gills for extracting oxygen, it’s not surprising that they’re such a successful group of animals. – I’m gonna ask one more
question before we move on here. I know some of the last
dissections we did, regenerations, of these, we passed that… – Yeah, we pretty much passed that phase. Most of these, once a limb
or a structure is lost, you know skin will regrow,
bone will even grow up to a certain point, but you’d not… Yeah, they don’t have the regeneration… – Like we’d seen in the past… – Right, right. (laid back electric guitar music)