Hello marine biology students.
In this video we're going to talk about the
physiology and behavior of fish.
[Intro Music]
So now that we've learned the types of fish,
let's learn about their functions.
So one aspect of fish has to do with their
coloration patterns and there are a few general
themes.
The first is countershading.
This is the case where the dorsal surface
is darker than the ventral or belly surface.
When seen from above, the darker coloration
of the dorsal surface blends in with the darker
color of the ocean bottom.
When seen from below, the lighter ventral
surface blends in with the lighter color of
the ocean surface.
And so, in this way they are camouflaged both
from above and below.
A more striking visual pattern is disruptive
coloration, which could include bars or stripes
that help break up the silhouette of the fish
for predator avoidance.
There is cryptic coloration, which is used
for camouflage and blending into the background,
whereas warning coloration is more an advertising
of one's presence to let predators know that
you are poisonous.
So, looking at some of these coloration patterns,
the shark and the tuna that we had seen earlier
has that counter shading, with a more darkly
colored upper surface or dorsal surface and
a lightly colored under surface.
In Figure (a), you might have a hard time
even seeing the rockfish on the bottom because
it's cryptic coloration is so matching that
of the seafloor, whereas a parrotfish rarely
matches its environment.
With this disruptive coloration, it might
make it more difficult for a predator to tell
where exactly the body is and where the body
is.
The lionfish is showing warning coloration
in that it is very poisonous and does not
want larger fish to attempt to eat it.
Not only do fish vary in their color, they
also vary in their overall body shape, and
these body shapes vary based on habitat and
lifestyle.
Fish can have different swimming habits, different
feeding habits, and these can all lead to
different body shapes.
Tuna, bill fish, and other fast-moving predators
are more likely to be streamlined, with their
fins serving as rudders.
Not only do fish have different body shapes,
they have different means of moving as well.
Often swimming is in a typical s-shaped pattern,
where most of the thrust is coming from the
tail.
Bands of muscle along the body of the fish
known as myomers end up driving that swimming
motion.
how four.
Different fins are used for different types
of forward movements.
Some will use their pectoral fins, some will
use their dorsal fins, others will use their
tails.
The gas-filled swim bladder of bony fish provide
buoyancy and the pectoral fins are usually
not used for lift in bony fish as they are
in sharks.
Sharks do not have a swim bladder, but they
do have a large lipid filled liver which helps
it with buoyancy.
Sharks tend to sink when not in motion, but
the large and stiff pectoral fins provide
lift.
The pectoral fins in many bony fish are flexible
and used for maneuverability, and in some
slow-swimming species, forward movement is
mainly provided by the pectoral fins.
Here we see a diagram of the general body
shape for sharks and bony fish and we can
see differences in the pectoral fins and the
presence of the swim bladder helps bony fish
with their buoyancy, whereas the heterocercal
tail and the stiff pectoral fins help provide
sharks with lift.
Whether we're talking about Chondrichthyans
or Osteichthyans, all fish have gills and
these gills are the equivalent of lungs for
animals on land.
These gills allow for gas exchange with the
environment.
The construction of the gills is the same
in all fish.
The gill arch provides support, whereas the
gill rakers are on the outer surface of the
gill arch.
The gill filaments trail behind the gill arch,
and in this diagram we can see the flow of
oxygenated water over the capillaries.
The way the gills are organized is that the
blood will be oxygenated as it moves between
the major vessels.
Diffusion of oxygen and carbon dioxide takes
place along the capillaries located in the
lamellae, that cover the gill filaments.
The efficiency of the diffusion 
of oxygen from high concentration to in the
water to low concentration in the blood is
increase because water flow across the lamellae
is the opposite direction to the blood flow.
The concentration of oxygen in the water is
always higher than that in the blood, and
so diffusion promotes that movement of the
oxygen into the blood.
The mouth of the fish tells us a lot about
its diet, because it will be specialized.
The beak or fused teeth of parrotfish is used
for grazing on algae and coral.
The long tube-like mouth of the butterfly
fish is perfect for feeding on individual
coral polyps or plankton, and the rows of
sharp teeth and wide mouth of the barracuda
captures its prey, other fish.
So the morphology of the mouth tells us about
the organisms’ food source.
The intestine, pyloric caeca, pancreas, and
liver all secrete digestive enzymes to aid
in the digestion of food.
The intestines of carnivorous fish tend to
be short and straight whereas the intestines
of herbivorous fish are usually longer and
more coiled, because plant and algal material
is more difficult to digest.
And so, here we can compare the organization
of the digestive system of a cartilaginous
fish and a bony fish.
Fishes have a two chambered heart.
This pumps blood throughout the body.
In contrast to the four chambered heart of
mammals and birds, arteries veins and capillaries
take blood to the body tissues and return
it to be reoxygenated and release of carbon
dioxide into the water by the gill filaments.
Oxygen and carbon dioxide are carried by the
hemoglobin
in the red blood cells, so unlike the two
circuits of blood flow that we see in mammals,
fish have only a single circuit of blood flow,
where oxygenated blood from the gills travels
to the rest of the body, gas exchange occurs,
deoxygenated blood returns to the heart, and
the heart sends that blood back to the gills
to repeat the process over again.
Because of diffusion, solutes and gases always
diffuse from a high concentration towards
a low concentration.
Marine fish are living in an environment where
the seawater has a high salt concentration
than that of their blood, so marine fishes
have a tendency to lose water and gain solutes.
Marine fish therefore need to osmoregulate
to prevent dehydration.
For marine fish, many swallow seawater, but
excrete that excess solutes or salts through
their kidneys or intestine.
Most marine fish pass very little, but concentrated
urine, to conserve water.
The opposite is observed in freshwater fish.
Cartilaginous fish, on the other hand, solve
the problem by keeping their blood at about
the same concentration as the seawater.
This is accomplished by keeping urea in the
blood.
Urea is a toxic metabolic substance that results
from the breakdown of proteins.
Urea is extreme ease and other vertebrates.
This means that there is a smaller tendency
to lose water and gain solutes in cartilaginous
fish than in bony fish, because the internal
and external conditions are more similar in
cartilaginous fish than in bony fish.
This also means that most cartilaginous fish
are not especially tasty or good to eat without
some sort of treatment to remove that excess
urea.
So, the solute concentration in the blood
of the cartilaginous fish is usually more
similar to that of the sea water than the
blood of bony fish.
Fish are vertebrates and therefore have a
complex nervous system.
They have a brain, spinal cord, and numerous
nerves like other vertebrates.
They have an olfactory sac 
for detecting chemical compounds in the water.
They have taste buds on their mouth, lips,
barbels, and skin.
In fish eyes, the position of the lens changes
like in a camera.
Color vision has evolved in many bony fish
and some sharks have a nictitating membrane
that can protect their eyes during feeding.
All fish rely heavily on their lateral line
system, which is the series of pores and canals
lined with cells known as neuromasts that
are specialized to detect vibrations.
These vibrations can indicate a predator or
prey or the position of other fish in a school.
Many fish also have sensory organs within
their inner ears.
These are fluid-filled canals with sensory
cells similar to the lateral line.
And as we had mentioned with chondrichthyans,
they have the ampullae of Lorenzini, which
allow them to detect electrical charges.
This can be very helpful in finding prey,
especially in murky water.
So here we can see the lateral line, its general
paths, along with the neuromast cells that
detect the vibration.
Then, not to mention the ampullae of Lorenzini
that allow sharks to detect electrical signals.
Schooling is a behavior that is seen in many
types of fish, but not all of them.
There are about 4000 species which will school
as adults, although many more fish school
as juveniles.
Schooling makes it possible for small fish
to appear much larger and thus avoid detection
by predators, as well as making it harder
for a predator to capture any one fish.
Many fish school as juveniles.
Fish will often have different patterns as
they are swimming in a school, whether they're
traveling in the same direction, feeding on
plankton, encircling a predator, or also avoiding
a predator.
Some fish are very territorial.
They establish and defend their territories
at all times.
Others might only be territorial during reproduction.
Fish normally maintained their territories
by showing aggressive behaviors called posturing.
This can include raising fins, opening mouths,
darting, even producing sound.
Fights between individuals are actually rare,
some fish species migrate between freshwater
and saltwater at different times in their
lives.
Anadromous species, such as salmon lampreys
and sturgeon, live in seawater but migrate
to freshwater to reproduce, whereas Catadramous
species
live in freshwater but travel to sea for reproduction.
Here we see the migration pattern of freshwater
eels both in Europe and North America.
These freshwater eels traveled to the Sargasso
Sea for reproduction and yet the larvae then
returned home into their appropriate continent
and water basins.
When it comes to reproduction, sex hormones
control the development of sperm and egg.
The release of sex hormones can be cued by
water temperature, day length, tidal cycle,
among others.
Broadcast spawning 
is the release of sperm and egg directly into
the water for fertilization, and this is most
common for marine fish.
Some fish do have internal fertilization in
which the sperm is inserted directly into
the female by the male.
Some species have complex mating behaviors
which are called courtship.
Courtship behaviors can be very choreographed,
from the female entering the territory, to
the male catching her attention, they swim
together, and finally copulation occurs.
A somewhat typical feature of fish reproduction
is that of biological sex reversal during
the course of an individual's life.
Protoandry 
is when individuals are male first and develop
into females later in life.
Protogyny is when individuals start as females
and then later develop into males.
These biological sex reversals can even happen
multiple times during the course of an individual's
life.
Most wrasses are born as males and there are
males through juvenile stages and early adulthood,
but once they reach a certain size, they become
females.
Yet, of those females, the largest converts
back into something known as a super male,
and that super male will typically lead a
harem of female fish.
But again, the larger of those female fish
might also turn into males.
The cues for these changes are often the result
of changes in social structure or environment.
In some anemone or clown fishes, a large female
mates only with the largest male.
If the dominant female dies, the largest male
then develops into the new female.
As we had seen with Chondrichthyans, fish
can be viviparous, oviparous
or ovoviviparous, meaning the young are either
born live in the case of viviparous.
Eggs are laid in the case of oviparous.
Or eggs are kept within the female and hatch
before being released from the females reproductive
tract in the case with ovoviviparous.
In most bony fish, eggs are laid by thousands
or millions and are not protected by the parents.
Another bony fish sometimes small numbers
of eggs are laid and the parents protect the
eggs.
Most reproduction involves external fertilization.
That's the case with broadcast spawners, however
internal fertilization
can happen and is especially common in the
cartilaginous fish.
This chart compares some of the features of
the common fish types, from the agnathan's
which are the hagfish and lampreys, the cartilaginous
fish, the rays and skates and sharks and ratfish,
and the bony fish the osteichthyans.
Well, a lot of the details of this chart are
too small to see in this slide.
I would highly encourage you to go to Table
8 1 in your book to look and compare these
different types of fish.
So that completes our discussion of fish physiology
and behavior.
Now, something I'd like you to consider before
our next video is, “If you had the choice
between living in water or on land, which
would you choose?”
We'll talk about that in the next video.
