Chapter 16 Notes, Fish
CHARACTERISTICS OF ALL FISH
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All fish are
aquatic
All fish are
vertebrates
All fish have gills
All fish have
appendages in
the form of fins
Most fish have
skin with scales
DIFFERENT GROUPS OF FISHES
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There are three main groups of fish.
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The jawless fishes are called the Agnathans.
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The cartilaginous fishes are called the
Chondrichthyes.
The bony fishes are called Osteichthyes.
THE AGNATHANS (JAWLESS FISH)
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Agnathans have a slender, eel-like body.
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Agnathans have naked skin, no scales.
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Agnathans have median fins only, no paired fins
like the pelvic or pectoral fins.
Agnathans have a cartilaginous skeleton and a
notochord, but a reduced or absent vertebrae.
Agnathans lack jaws, but they have mouths that
are adapted to parasitism or scavenging.
LAMPREY ANATOMY
THE AGNATHANS
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One class of Agnathans is called Myxini
The types of fish that are found in the class
Myxini are called hagfishes.
Hagfish are a marine fish that feed on dead or
dying animals like fish, annelids, molluscs,
crustaceans and marine mammals.
Most hagfish are scavengers. They are almost
completely blind, but they have an acute sense
of smell. They are attracted to dead flesh.
HAGFISH
THE AGNATHANS
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The hagfish attach to their food with their teeth
and they tear off pieces of flesh with their rasplike tongue. In order to achieve more leverage
they can form a knot in their body and push the
knot in their body against the body of their prey.
Hagfish are also well known for their unique
ability to produce enormous amounts of slime.
Another class of Agnathans is called class
Cephalaspidomorphi. Fish in this class of
Agnathans are called lampreys.
AGNATHANS (JAWLESS FISH)
THE AGNATHANS
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Most lampreys are ectoparasites and attach
to the skin and feed on the blood of their host.
In North America, marine and freshwater
lampreys spawn in the winter or spring in
shallow gravel or sand in freshwater streams.
Adults die soon after spawning, then the eggs
hatch in approximately 2 weeks, and produce
small larvae called ammocoetes.
LAMPREYS ON A LAKE TROUT
THE AGNATHANS
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The ammocoetes feed on small invertebrates.
After the ammocoetes metamorphose into
adults, they migrate to the sea or stay in the
freshwater streams and attach to a fish host with
their teeth and suck their blood.
To promote the flow of blood, lampreys inject an
anticoagulant into the wound.
Lamprey eels were an invasive species to the
Great Lakes region in the 1950's and they almost
completely decimated the lake trout fishery.
AMMOCOETES (LAMPREY LARVA)
CLASS CHONDRICHTHYES
(CARTILAGINOUS FISHES)
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Chondrichthyes have a cartilaginous skeleton.
Chondrichthyes have placoid scales, which are
anatomically similar to their teeth.
Chondrichthyes have a j-shaped stomach with a spiralvalved intestine.
Chondrichthyes have exposed gill slits with no operculum
(protective gill plate that covers the gills).
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Chondrichthyes do not have a swim bladder.
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For buoyancy they have an oily liver filled with squalene.
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Most Chondrichthyes exhibit internal fertilization.
PLACOID SCALES AND EXTERNAL
GILL SLITS
SUBCLASS ELASMOBRANCHII
(SHARKS AND RAYS)
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About half of elasmobranchs are sharks.
Sharks are typically predators with 5-7 pairs of
gills and gill slits.
Sharks have a spiracle or opening behind each
eye that is used to bring water to the gills.
Sharks are heavier than water, so they must
continue to swim forward or they will sink.
Sharks vary is size from the harmless planktoneating whale shark (15 meters), to the spiny
dogfish sharks that rarely exceed 1 meter.
SHARK ANATOMY
SUBCLASS ELASMOBRANCHII
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Sharks have an assymetrical heterocercal tail.
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The heterocercal tail provides lift and thrust.
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The broad head and pectoral fins also help
provide lift in the water.
The placoid scales of the shark reduce
turbulence. The teeth of the shark resemble the
placoid scales and are replaceable.
The placoid scales are made of dentine and
enamel, just like teeth.
HETEROCERCAL TAIL OF A SHARK
SUBCLASS ELASMOBRANCHII
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Sharks have an extremely good sense of smell
and a system of canals on the sides of the body
that can detect vibrations called a lateral line.
At close range, the shark relies on vision and
special sensory receptors called the ampullary
organs of Lorenzini to detect their prey.
The ampullary organs of Lorenzini can detect
bioelectric fields that surround all animals.
Male sharks have a clasper on their pelvic fins
that transfers sperm internally to the female.
AMPULLARY ORGANS OF LORENZINI
SUBCLASS ELASMOBRANCHII
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Many sharks and skates are oviparous, and
lay their eggs after fertilization.
Most sharks are ovoviviparous, meaning
fertilization is internal, eggs are developed
and hatched internally. The young receive
nourishment via a yolk sac rather than a
placenta. Young are born live.
Some sharks are viviparous, meaning the
young are not in an egg but a placenta, and
the young are born live after development.
SHARK CLASPERS
SUBCLASS ELASMOBRANCHII
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About half of the elasmobranchs are rays.
Rays are a group of fish that includes skates,
stingrays, electric rays and manta rays.
Rays have a dorsoventrally flattened bodies
and enlarged pectoral fins, which they move in
a wave-like motion to swim through the water.
Rays have large spiracles on top of their head
because they often bury their mouth in the
sand while hunting. This prevents clogging of
the gills with sand and debris while hunting.
SUBCLASS ELASMOBRANCHII
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Stingrays have a long,
slender, whiplike tail that is
armed with saw-toothed
spines that can inflict
dangerous wounds.
Electric rays have muscles
on the side of their head that
can produce powerful
electrical fields that can
shock and stun their prey.
6'' stingray tail barb
STINGRAYS
THE BONY FISHES
(OSTEICHTHYES)
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Bony fish have a skeleton made of bone.
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Most bony fish have a homocercal tail.
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Scales of bony fish are either cycloid , ctenoid, or
occasionally ganoid (like gar).
Bony fish have a hard protective covering over the gills
called the operculum.
Bony fish have a swim bladder that allows them to achieve
neutral buoyancy.
SCALES TYPES
THE BONY FISH (OSTEICHTHYES)
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There are two classes of bony fish; the ray-finned
fishes (Actinopterygii), and the lobe-finned fishes
(Sarcopterygii).
One advantage of the bony fishes is having the
operculum, which not only protects the gills, but
increases efficiency by allowing the fish to
actively pump water across the gills.
some bony fishes can use their swim bladder and
their gills for respiration.
THE OPERCULUM
THE RAY-FINNED FISHES (CLASS
ACTINOPTERYGII)
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The ray-finned fishes have spiny rays in their fins that
help them control their movement.
Within the ray-finned fishes there are three different
groups of fishes; the chondrosteans, the holosteans,
and the teleosts.
The chondrosteans are a rare group of fish that are
mostly extinct and mostly found in the fossil record.
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They have a partial cartilaginous and bony skeleton.
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Some also have a heterocercal tail and spiracles.
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Some examples of extant (living) chondrosteans
include sturgeons, bichir (pronounced bee-SHEER),
and the paddlefish.
CHONDROSTEANS
MONSTER STURGEON FROM THE
FRAZER RIVER IN BRITISH
COLUMBIA, CANADA
THE RAY-FINNED FISHES (CLASS
ACTINOPTERYGII)
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The next group of ray-finned fishes called the
holosteans is also more common in the fossil
record than in species alive today.
Bowfins and gars are extant (living) holostean fish.
One common characteristic of the holostean fish
is the presence of ganoid scales.
Ganoid scales are hard diamond-shaped scales
made of a hard substance called ganoin.
HOLOSTEANS (GAR AND BOWFIN)
GANOID SCALES AND ALLIGATOR GAR
THE RAY-FINNED FISHES (CLASS
ACTINOPTERYGII)
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The last group of fish in class Actinopterygii are
called teleosts.
Teleosts are the most abundant and diverse
group of fish. They make up 96% of all living
fish, and almost half of all the vertebrates.
Their scales are lightweight, thin, and flexible,
and they are arranged in overlapping layers.
The two most common types of scales of the
teleosts are cycloid scales and ctenoid scales.
THE RAY-FINNED FISHES (CLASS
ACTINOPTERYGII)
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Most of the teleosts have a homocercal tail.
The homocercal tail allows for more thrust and
rapid bursts of speed.
Features of the teleosts such as lightweight
and flexible scales, and a homocercal tail have
made the teleosts some of the most successful
groups of fish and vertebrates in the world.
THE LOBE-FINNED FISHES
(CLASS SARCOPTERYGII)
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The Lobe-Finned fishes (class Sarcopterygii)
have fleshy lobes or appendages which allow
them to move around in the shallow water.
Lobe-finned fishes also have a diphycercal tail,
which is not very efficient for moving fast.
More useful for crawling through the mud.
The coelacanth and lungfishes are examples of
lobe-finned fish in the class Sarcopterygii.
There are only 6 living species of lungfish and
2 known living species of coelacanth.
THE LOBE-FINNED FISHES
(CLASS SARCOPTERYGII)
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The Australian lungfish can survive in hot,
stagnant, oxygen-poor waters by coming to the
surface and gulping air into its swim bladder.
The South American and African lungfish can
burrow in the mud in a drought and live without
water for several weeks or months at a time.
During the dry season, the African lungfish
secretes large amounts of slime that mixes
with mud to form a hard cocoon. It remains
dormant in the cocoon until after it rains.
LUNGFISH
THE LOBE-FINNED FISHES
(CLASS SARCOPTERYGII)
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Coelacanths were once believed to be a fish that
was extinct for 70 million years.
In 1938, a fishing trawl caught the remains of a
coelacanth off the coast of South Africa by the
island of Madagascar.
An intensive search began and scientists were
successful at catching some live specimens.
In 1998, a new species of coelacanth was
discovered in Indonesia, 5,000 miles away.
The eggs of the coelacanth are unusually large (9
cm). They hatch fully formed from the egg.
COELACANTH
LOCOMOTION IN WATER
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The muscle structure of fish is composed of zig
zag, w-shaped myomeres.
The unique arrangement of the myomeres allows
for more power and control.
Fast moving fish like the tuna, marlin, swordfish,
and wahoo all have broad bodies, narrow caudal
peduncles, and sickle-shaped tails.
More surface area on the head and tail (more
forward motion), and less surface area on the
caudal peduncle reduces resistance in the water,
and increases a fishes swimming efficiency.
TAIL AND BODY SHAPE OF A FAST
MOVING FISH
NEUTRAL BUOYANCY
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All fishes are slightly heavier than water.
To keep from sinking, sharks have to keep
moving and they have a heterocercal tail.
Sharks also have a very large liver filled with
an oily substance known as squalene.
Squalene is less dense than water (0.86
g/mL) and helps the shark to not sink.
Bony fish use a gas-filled swim bladder to
achieve neutral buoyancy.
RESPIRATION
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Gills in bony fish have a protective operculum
and four gill arches that support the gills.
Gill rakers project forward on the gill arches
and strain out food and debris.
Gill filaments project back from the gill arches.
Gill filaments are made up of fine plate-like
structures called lamellae.
The lamellae are richly supplied with blood
vessels (capillaries).
ANATOMY OF THE GILLS
RESPIRATION
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The blood vessels in the lamellae run in the
opposite direction that water flows over the gills.
This is a remarkable adaptation of fish that
allows up to 85% or more oxygen saturation.
This adaptation is called countercurrent flow.
If the blood flowed in the same direction as the
water flowed over the gills, the maximum
amount of oxygen saturation could never be
more than 50%.
COUNTERCURRENT FLOW
HOW COUNTERCURRENT FLOW WORKS
OSMOREGULATION
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Freshwater fish are hyperosmotic regulators,
because they live in an environment with low
concentrations of salt. Salt-absorbing cells in
their gills actively pump salt into their bodies
and their kidneys produce diluted urine.
Marine fish are hypoosmotic regulators,
because they live in an environment with a high
concentration of salt. Salt-secreting cells in
their gills actively pump salt out of their bodies
and their kidneys produce concentrated urine.
OSMOREGULATION
MIGRATION
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Some fish spend a period of their life in both
fresh and salt water. This type of migratory
behavior is called being diadromous.
Some fish like freshwater eels, are
catadromous, meaning they spend most of
their adult life (6-10 years) in freshwater, and
migrate to the ocean where they spawn.
After the young of the eel hatch, they are in
the form of leaf-shaped larva called
leptocephali.
AMERICAN EEL LIFE CYCLE AND MIGRATION
MIGRATION
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The leptocephali of the eels begin a long
migration to freshwater streams. After about a
year, they develop into juvenile eels called
elvers. The elvers then will then eventually
mature and develop into adult eels, which will
return to the ocean to spawn in 8-15 years.
Migrating Salmon do the opposite.
Salmon are anadromous, meaning they spend
most of their adult lives at sea, and migrate to
freshwater to spawn.
MIGRATION
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The Atlantic salmon and the steelhead can
make spawn multiple times. Pacific salmon all
die after they have spawned only once.
Salmon have a remarkable homing instinct.
The smolt of the salmon, migrate downstream
to the ocean. Once there, they spend 3-5 years
in the ocean wandering hundreds of miles.
Then, they almost always return to the exact
same stream where they were born.
MIGRATION
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Occasionally adult salmon stray from stream to
stream to allow mixing of the gene pool.
Studies have shown that what allows salmon to
find their own stream is they imprint the distinct
odor of the stream where they were born.
It is believed that the odors they smell are a
combination of compounds released by the
surrounding vegetation and soil of the stream.
They also imprint the streams downriver where
they were born to create a mental map.
PACIFIC SALMON LIFE CYCLE
REPRODUCTION
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We already discussed reproduction in
Elasmobranchs (Sharks and Rays).
Bony fish are almost all oviparous, which means
they lay and fertilize their eggs externally and the
young develop externally.
There are some examples of ovoviviparous bony
fish like mollies and guppies.
The strategy of most bony fish in reproduction is
to produce as many eggs as possible because
the mortality rate is high.
REPRODUCTION
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Many pelagic (open ocean) fish release their eggs
directly into the open water. Their eggs are
buoyant and float with the ocean currents.
Many near shore and benthic (bottom dwelling) fish
release eggs that are nonbuoyant and adhesive, so
they will stick to the bottom substrate in order to
prevent them from drifting away.
After eggs are released and fertilized, the eggs
eventually hatch into alevin.
Alevin have a yolk sac that provides nourishment.
EGGS AND ALEVIN