What is a Fish?
• Vertebrates
• Live in water
– 40% are freshwater
– 60% are marine
• Gills for breathing
• Fins
• Ectothermic
Important Terms
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Ventral – bottom side
Dorsal – back side
Anterior – front end (head)
Posterior – tail end
Fish Fins
• Caudal fin – tail – forward movement (in most)
– Heterocercal – upper lobe is longer than lower lobe
– Homocercal – upper and lower lobes are same size
• Dorsal Fin – balance and stability
– Can have 1-3 dorsal fins
• Pectoral Fin – dynamic lift, “walking”, steering
– Forward movement in rays and skates
• Pelvic Fin – up/down movement, steering,
stopping
• Anal Fin – balance and stability
Heterocercal Tail
Homocercal Tail
Fish Fins
Fish Fins – Sharks
Evolution
• The first fishes probably evolved in the
ocean around 500 million years ago.
• First fish are thought to be jawless, but did
have a digestive system and a chordate body
plan.
• Early jawed fishes were far more successful
at eating invertebrates with shells or
exoskeletons.
• These jawed fish were also equipped with
paired fins to stabilize movements
Evolution
• The numbers and types of jawed fishes increased
dramatically beginning about 410 million years ago.
• By the end of the Devonian period (aka the Age of the
Fishes), from 408 to 360 mya, jawed fishes had spread
into a vast number of habitats.
• The ancestral jawed fishes gave rise to cartilaginous
fishes and bony fish.
Hagfish and Lampreys
CLASS AGNATHA
Class Agnatha
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Jawless (“A” = lacking, “gnathos” = jaw)
No paired appendages to aid in locomotion
Gill slits
Some have openings called slime glands
Round, sucking mouth surrounded by
organs sensitive to touch and smell.
• Degenerative eyes covered by a thick skin
• Body ends in a flattened tail (movement)
http://www.youtube.com/watch?v=letqkpG3b5Q
Hagfish
http://www.youtube.com/watch?v=Bb2EOP3ohnE
Lampreys
Sharks, Skates, Rays, and Ratfish
CLASS CHONDRICHTHYES
Chondrichthyes Basics
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“Chondros” = cartilage, “ichtyhs” = fish
Includes sharks, skates, rays, and ratfish
Skeleton is made of cartilage
Rough skin covered by placoid scales
Jaws with teeth
Paired lateral fins
Often active lifestyles.
Sharks
• 350 species
• Nearly all are marine
• No gas bladder – will sink if they stop
swimming
• Fusiform (spindle shaped) – hydrodynamic
• Caudal fin is well developed and powerful –
usually heterocercal
• Usually two dorsal fins, first of which is
typically larger and triangular
• 5 -7 gill slits
Sharks
• Powerful jaws have rows of numerous sharp teeth
• Lost or broken teeth are replaced by another,
which slowly shifts forward from the row behind it
as if on a conveyor belt
• Can have between 5 and 15 rows of teeth
• Some sharks are thought to go through 12000 50000 teeth in a lifetime
– Tiger sharks – 24000 teeth in a 10 year period
Sharks
• Sharks are in danger!
• Hunted for meat, oil, skin (leather,
sandpaper), fins (soup), cartilage (“joint
nutrient”)
• US has a ban on shark finning
• Many countries have strict laws and
regulations pertaining to shark hunting
Shark Fun Facts
• Great White Shark is probably the most
dangerous – can reach 7 meters (23 ft) and
1,400 kg (3,000 lbs)
• The largest shark species, the whale shark,
reaches in excess of 18 m (60 ft) and 41000
kg (90000 lbs)
• Whale sharks and basking sharks are docile
and feed on plankton.
• Smallest shark is the spined pygmy shark –
10 inches long
Shark Videos
• http://www.youtube.com/watch?v=E9kkfX1d
6N4&feature=player_embedded
• http://www.youtube.com/watch?v=W_L9vj3
e2sU&feature=channel
The Dreaded Great White Shark
Mako Shark
Hammerhead Shark
Tiger Shark
Whale
Shark
Spined Pygmy
Shark
More Sharks
Goblin Shark
Blacktip Shark
Sawshark
http://www.youtube.com
/watch?v=eh_HUIJkRzU&
safety_mode=true&persis
t_safety_mode=1
Rays and Skates
• Approx 500 species
• Dorsoventrally flattened bodies
• Live on the ocean bottom for the most part
– called demersal
• 5 prs of gill slits on the ventral side
• Pectoral fins are flat and greatly expanded
and fused to the head
• Eyes usually on top of head
Rays
• Stingrays, eagle, bat, manta, and cow-nosed
rays
• Whip-like tail usually equipped with stinging
spines at the base for defense
– Some are poisonous
• Many bury themselves in the sand, making
them almost invisible
• Feed on clams, crabs, small fish, and other small
animals that live in the sediments
– Teeth are modified into grinding plates that can
crush prey
• Give birth to live young
Eagle Ray
Bat Ray
Marble Ray
Cownose Ray
Manta Rays
Can reach up to 7 m (23 ft) wide
Electric Rays
• Have specialized organs that produce
electricity on each side of the head
• Can deliver shocks up to 200 volts that stun
the fishes they eat and discourage predators
Skates
• Lack a whip-like tail and stinging spines
• Some have electric organs
• Lay egg cases
Ratfish – aka Chimaeras
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About 30 species
Mostly found in deep water
One pair of gill slits covered by a flap of skin
Some have a long rat-like tail
Feed on bottom-dwelling crustaceans and
molluscs
Chimaeras
Bony Fish
CLASS
OSTEICHTHYES
Class Osteichthyes – Bony Fish
• 23,000 species – 96% of all fishes and almost
half of all vertebrates
– 75 – 100 new species are discovered every year!
• Skeleton made at least partially of bone
• Cycloid or ctenoid scales, or no scales at all
– Cycloid scales are smooth
– Ctenoid scales have many tiny spines along their
exposed borders
• The scales are made of bone and are
covered by a thin layer of skin as well as a
protective mucus
Scale
Types
Ctenoid Scales –
See the tiny little spines?
Placoid Scales –
Found in Sharks
Cycloid Scales
Osteichthyes Characteristics
• Operculum, or gill cover – flap of bony plates
and tissue that protects the gills
• Homocercal tail
• Fins generally consist of thin membranes
that are supported by bony spines, or fin
rays
• Fin rays may consist of rigid spines that act
as rudders or are used for protection; some
are flexible and used for propulsion and
added maneuverability
Operculum and Gills
Fin Rays
Homocercal Tail
Osteichthyes Characteristics
• Mouth is typically located on the anterior end
(head)
• Jaws have much more freedom of movement
– Protrusible because they can be projected outward
from the mouth
• Teeth are generally attached to the jawbones
• Most have a swim bladder, a gas-filled sac just
above the stomach and intestine
– Allows the fish to adjust buoyancy
– Significant development that compensates for the
relatively heavy bony skeleton
Physiology
BIOLOGY OF FISH
Biology of Fishes
• Ichthyology – the scientific study of fishes
• Fishes are extraordinarily diverse in shape, size,
color, feeding habits, reproductive patterns,
and behavior.
• They have adapted to nearly every type of
marine environment and all land vertebrates
evolved from them.
• For cartilaginous and bony fish, we will look at:
*Body Shape *Coloration *Locomotion
*Feeding
*Digestion *Circulatory System
*Respiratory System
*Behavior
*Regulation of Internal Environment
*Nervous System and Sensory Organs
*Reproduction and Life History
Body Shape
• Streamlined body – fast swimmers – helps move
through water
• Laterally compressed body – good for leisurely
swimming around coral reefs, kelp beds, or rocky
reefs, but are still efficient enough to allow for bursts
of speed to escape enemies or capture prey
• Dorsoventrally flattened body – adapted for life on
the bottom
• Laterally flattened – also adapted for life on the
bottom – begin life with one eye on each side of
head, but as they develop one eye migrates up to lie
next to the other one
• Elongated bodies – allow for shelter in small, narrow
spaces in rocks or coral reefs
Streamlined
Baracuda
Tuna
Tang
Angelfish
Laterally Compressed
Dorsoventrally Flattened - Rays
Laterally Flattened - Flounder
Elongated Bodies – Eels
Body Shapes can be especially useful
for camouflage
Pipefishes live
among the eelgrass
they resemble
Trumpetfish often hang vertically
among gorgonian corals or
tube-like sponges
Coloration –Chromatophores
• Tropical bony fish tend to be brightly colored
• Chromatophores – special skin cells that
contain colored pigments
• The amazing variety of colors and hues
observed among marine fishes results from
combinations of chromatophores with
varying amounts of different pigments
• Many fishes can rapidly change color by
contracting and expanding the pigment in
the chromatophores.
Coloration
• Fishes may also have structural colors that result
when a special surface reflects only certain colors
of light.
– Most are the consequence of crystals that act like tiny
mirrors
– The crystals are contained in iridophores
Coloration
• Fish can change colors for:
– Mood
– Reproductive condition
– Warning coloration – advertise danger, poison,
or bad taste
– Cryptic coloration – camouflage to deceive
predators or prey
– Disruptive coloration – the presence of color
stripes, bars, or spots that help break up the
outline of a fish – confuse predator
• Color changes are common among coral reef
fishes!
Warning Coloration – Blue Ray
Cryptic Coloration – Frogfish
Warning Coloration –
Thornback Cowfish
Cryptic Coloration –
Halimeda Ghost Pipefish
http://video.nationalgeographic.com/video/player/places/parks-and-nature-places/oceans/oceans-caribbean-gulf.html
Disruptive Coloration –
Ornate Cowfish
Disruptive Coloration –
Fimbriated Moray Eel
Coloration - Countershading
• Open-water fishes and many shallow-water
predators are rarely colorful.
• Most have countershading – silver/white
ventral side, dark dorsal side
– Form of camouflage in open waters
• Deep-water fishes tend to be black or red,
both of which are hard to see in the ocean
depths.
Countershading
Whale Shark
Yellowtail Kingfish
Clown Triggerfish
Great White
Locomotion
• Fishes swim to obtain food, escape from
predators, find mates, and, for some, swimming
flushes gills with water to obtain oxygen.
• Most fishes swim with a rhythmic side-to-side
motion of the body or tail.
• S-shaped waves of contractions moving from
head to tail push against the water and force
the body forward.
– Rhythmic contractions are produced by bands of
muscles called myomers, which run along the sides
of the body.
Feeding – Cartilaginous Fish
• Most sharks are carnivorous!
• However, several species of cartilaginous fishes
are filter feeders – whale shark, basking shark,
manta and devil rays.
• Filter-feeding fish filter the water with their gill
rakers, slender projections on the inner surface
of the gill arches.
• The width of space between the gill rakers
determines the size of food captured.
• Water is strained through the gill rakers, and
the fish swallows the food that is left behind.
Carnivorous Great White
Filter Feeding Basking Shark
Feeding – Bony Fish
• Bony fish are very diverse when it comes to
feeding methods.
• Most are carnivores
• Capture their prey from sediments, the water
column, the surface of rocks, or from other
organisms, including other fishes.
• Some chase their prey, others sit and wait.
• Carnivorous bony fishes typically have welldeveloped teeth for catching, grasping, and
holding their prey which is usually swallowed
whole.
Feeding – Bony Fish
• Grazers – feed primarily on seaweeds and
plants
• Filter feeders – filter plankton using gill
rakers.
– usually found in large schools
• Plankton feeders are the most abundant
fishes in the ocean
– Important food source for many types of
carnivores
Parrotfish – use beak to graze
on small algae and coral
Butterfly fish – uses a long
snout and mall mouth to
feed on very small prey
Barracuda – tears of chunks of prey
Herring – has a large mouth
for filter feeding
Digestion
• Pathway of food:
– swallow  pharynx  esophagus  stomach
(digestion starts here)  intestines  cloaca
• In bony fish, enzymes are realeased by:
– Pyloric caeca (anterior portion of intestine)
– Pancreas
– Inner wall of intestines
• The liver is also important because it secretes
bile which is needed for the breakdown of fats.
– The liver is particularly large and oil-rich in sharks,
sometimes making up as much of 20% of their body
weight.
– The liver also plays a huge role in detoxifying the
blood in all vertebrates
Digestion - Intestines
• Carnivorous fishes have short, straight
intestines.
• Herbivorous fishes have coiled intestines
• Many cartilaginous fish contain a spiraling
portion of the intestine called the spiral valve
– Increases the internal surface area
• The intestine is responsible for absorbing the
nutrients
– Nutrients pass into the blood to be distributed
through the body.
• Undigested material exits through the anus, or
the cloaca, the common passage for the
digestive, excretory, and reproductive systems
in cartilaginous fishes.
Anatomy of a Fish – The Digestive System
Circulatory System
• All fishes have a two-chambered heart that
is located below the gills.
• Pathway of blood:
– Veins  1st chamber of heart  2nd chamber of
heart  gills  arteries  capillaries  veins
• Gas exchange takes place in the gills
– Blood picks up oxygen and releases carbon
dioxide
Anatomy of a Fish –
Circulatory System
Ateries
Capillaries
Gills
Heart
Veins
Respiratory System –
Cartilaginous Fish
• Irrigation of the Gills – Cartilaginous Fish
– Swimming, plus the opening and closing of the
mouth, forces water through the mouth, over
the gills, and out through the gill slits.
– The first pair of gill slits of cartilaginous fishes is
modified into spiracles (round openings behind
the eyes)
– Spiracles allow intake of water even when the
ventral mouth is buried in the sediments.
Spiracles
Respiratory System – Bony Fish
• Irrigation of the Gills – Bony Fish
– Bony fish have a more efficient mechanism.
– The gills on each side share a common gill
chamber, which opens to the outside through an
opening on each side of the head.
– Each opening is covered by an operculum
– When the mouth opens, the opercula close and
the pharynx expands, sucking water in.
– The opposite happens to pump the water out.
Irrigation of the Gills
Respiratory System – Structure of the Gills
• Gills are supported by cartilaginous or bony
structures, called gill arches.
• Each gill arch bears two rows of slender fleshy
projections called gill filaments.
• Gill rakers project along the inner surface of the gill
arch that prevent food particles from entering and
injuring the gill filaments or may even be specialized
for filtering the water in filter-feeding fishes.
• The gill filaments have a rich supply of capillaries that
contain oxygen-rich blood, which gives gills their
bright red color.
• Each gill filament contains many rows of thin plates
called lamellae, which also contain capillaries.
• Lamellae greatly increase the surface area through
which gas exchange can take place.
Gills
Respiratory System – Gas Exchange
• Oxygen dissolved in the water diffuses into the
capillaries of the gill filaments to oxygenate
blood.
• Diffusion will take place only if oxygen is more
concentrated in the water than in the blood.
• As oxygen diffuses from the water to blood in
the capillaries, the amount of oxygen in the
water decreases and that in the blood
increases.
• Fishes have evolved an adaptation called a
countercurrent system of flow to increase the
efficiency of gas exchange.
– The blood in the gills flows in the opposite direction
to the water passing over them.
Respiratory System – Gas Exchange
• The blood disposes of its carbon dioxide using the
same mechanism. Blood flowing into the gills from
the body has a high concentration of carbon dioxide,
while the water has a low concentration  The
carbon dioxide diffuses out of the blood and into the
water
• Once oxygen enters the blood it is carried through
the body by hemoglobin, a red protein that gives
bloods its color.
• Hemoglobin carries oxygen to the tissues as it is
needed and picks up the carbon dioxide and takes it
to the gills.
• Muscles use a lot of oxygen during exertion so they
need to be able to store excess oxygen. Muscles
have a protein called myoglobin.
Gas Exchange – Red Blood Cells
Regulation of the Internal
Environment – Bony fish
• The blood of marine bony fishes is less salty than
seawater.
• As a result they lose water by osmosis.
• Marine bony fishes therefore need to osmoregulate
to prevent dehydration.
• To replace lost water, they swallow seawater, which
contains excess salts, some of which pass straight
through the gut without being absorbed.
• Salts that are absorbed are excreted by the kidneys
(the most important excretory organs of
vertebrates) and specialized chloride cells in the gills.
• The kidneys conserve water by producing only small
amounts of urine.
Regulation of the Internal Environment –
Cartilaginous fish
• Cartilaginous fish reduce osmosis by increasing the
amount of dissolved molecules, or solutes, in their
blood, making the blood concentration closer to that
of seawater.
• They retain a chemical called urea, a waste product
that results from the breakdown of proteins.
• The amount of urea in the blood is controlled by the
kidneys
• Cartilaginous fish also absorb water to prevent
dehydration, mostly through the gills and from food.
• Excess salts are excreted by the kidneys, intestine,
and a special gland near the anus called the rectal
gland.
The Central Nervous System – In General
• Vertebrates have the most complex and
advanced nervous system of any animal group.
• At the heart of the nervous system is the
central nervous system (CNS), consisting of the
brain and spinal cord.
• The CNS coordinates and integrates all body
activities and stores information.
• The brain is divided into several regions each
having a particular function.
• The brain is protected by a cartilaginous or
bony skull and is connected to the rest of the
body by nerves.
Can Fish Smell?
• Most fishes have a highly developed sense of
smell, which they use to detect food, mates,
and predators, and sometimes to find their way
home.
• Fishes do this with a special sensory cells
located in olfactory sacs on both sides of the
head.
• Each sac opens to the outside through one or
two openings, the nostrils, or nares.
• Sense of smell is well developed in sharks –
They can detect blood in concentrations as low
as fractions of one part per million!!!
Can you see his olfactory sacs?
Barreleye
Do fish have the ability to taste?
• Fishes detect some chemical stimuli with
taste buds located in the mouth and on the
lips, fins, and skin.
• Taste buds are also found on barbels,
whisker-like organs near the mouth of many
bottom feeders, such as marine catfishes.
How Do Fish See?
• Fishes have eyes that only focus as they
move closer and further away from an
object
– Most vertebrates change the shape of the lens
to focus!
• Bony fish rely on vision more than
cartilaginous fish.
• Some sharks have a distinct nictitating
membrane that can be drawn across the eye
to reduce brightness and to protect the eye
during feeding.
Fish Eyes
The Lateral Line
• Fishes have a unique sense organ called a lateral line
that enables them to detect vibrations in the water.
• It consists of a system of small canals that run along
the head and body.
• The canals lie in the skin and in the bone or cartilage
of the head.
• The canals are lined with clusters of sensory cells, or
neuromasts, that are sensitive to vibration.
• The lateral line picks up vibrations from the
swimming of other animals and from sound waves.
• This allows fish to avoid predators, detect prey,
orient to currents, and travel in a school.
Can You See the Lateral Line?
Ampullae de Lorenzini
• Cartilaginous fish have sense organs in the head
called ampullae de Lorenzini that can detect weak
electrical fields.
• Helps the fish detect and locate prey
• Also thought to help in navigation (used as a sort
of compass) and possibly even to detect currents.
The Inner Ears
• Fishes can perceive sound with inner ears,
paired hearing organs located to the sides of
the brain just behind the eyes.
• In some fishes the swim bladder amplifies the
sound by vibrating and transmitting sound
waves to the inner ear.
• Also involved in equilibrium and balance.
• Many fishes detect changes in body position
from movement of calcareous ear stones, or
otoliths, that rest on sensory hairs, a
mechanism similar to the statocytes in
invertebrates.
Behaviors
• Nearly all aspects of the lives of fishes involve
complex behavior to adapt to light and
currents, to find food and shelter, and avoid
predators.
• Behavior is also an important part of fish
courtship and reproduction.
• In this section we will look at behaviors
pertaining to:
– Territoriality
– Schooling
– Migrations
Behavior: Territoriality
• Some fishes are known to establish territories,
home areas that they defend against intruders.
• Some defend territories only during reproduction
while others defend their territory permanently
because they may use it for food and shelter.
• Territoriality is most common in crowded areas like
coral reefs and kelp beds.
Damselfish are particularly
nasty when it comes to
defending their territory.
Sometimes they attach
individuals much larger than
themselves, including divers!
Behavior: Territoriality
• Fishes use a variety of aggressive behaviors to
defend the territories.
• Its rare that a fish fight will actually break out – its
more of a bluffing game!
• Fishes have threatening postures – raised fins, an
open mouth, and rapid darting about are examples
• Other fish (mainly bony fish) make threatening
sounds – grinding their teeth, rubbing bones, or
rubbing fin spines on other bones
• Some fishes “drum” by pulling muscles on the swim
bladder, and this sound is amplified by the air-filled
bladder.
Behavior: Schooling
• Many fishes from well-defined groups, or schools.
• It has been estimated that around 4,000 species,
both marine and freshwater, school as adults.
– Includes herrings, sardines, mullets, and some
mackerels.
– Some cartilaginous fish school too – hammerheads and
manta rays
• Schools function as well coordinated units, though
they appear to have no leaders.
• The individual fishes tend to keep a constant
distance between themselves, turning, stopping, and
starting in near perfect unison.
• Fish can use vision, the lateral line, olfaction, and
sound to keep track of each other.
Behavior: Why Do Fishes School?
• Schooling offers protection against predation.
– Predators may be confused if the school circles or
splits up.
– It also makes it tough for predators to focus on one
fish if the school is shifting, and darting.
• Schooling increases the swimming efficiency of
the fish because the fish in front form an eddy
that reduces water resistance for those behind.
• Schooling can also be advantageous in feeding
or mating.
• However, reasons probably vary from species
to species and may occur for multiple reasons.
Behavior: Migrations
• Another interesting behavior of marine fishes is
migration, regular mass movements from one place
to another once a day, once a year, or once in a
lifetime.
• Schools can migrate onshore and offshore to feed.
• Many open-water fishes migrate several hundred
meters up and down the water column every day to
feed.
• Other fishes make transoceanic migrations – tunas,
salmons, etc.
• Feeding is usually the main reason for migration.
Behavior: Migrations
• However, some migrations take place for
breeding purposes.
• Some fishes migrate between sea and fresh
water for reproduction.
• Anadromous fishes spend most of their lives at
sea but migrate to freshwater to breed.
– Examples: Sturgeons, lampreys, smelts, and salmon
• Catadromous fishes have a migratory pattern
opposite that of salmon – the breed at sea and
then migrate into rivers to grow and mature.
– Examples – at least 16 species of eels
Salmon
• After several years at sea,
salmon mature sexually and
start migrating into rivers.
• Salmon find their home
streams with remarkable
accuracy, using a type of
chemical memory.
• They recognize the “smell”
of their home stream, along
with the “smells” of all the
other streams on their way.
• The ability to find their way
back to their home area is
called homing behavior.
Reproductive System
• The sexes of fish are usually separate with both
sexes having paired gonads located in the body
cavity.
• In cartilaginous fishes, ducts lead from the ovaries
and testes into the cloaca, which opens to the
outside.
• Jawless and bony fishes have a separate opening for
urine and gametes, the urogenital opening, which is
located just behind the anus.
• In many marine fishes the gonads produce gametes
only at certain times. The timing of this production is
crucial – Both sexes must be ready to spawn at the
same time.
• Spawning, as well as larval development, must take
place during the period with the most favorable
conditions.
Reproductive System – Sex
hormones
• The timing of reproduction is controlled
mostly by sex hormones, which are
produced in the gonads and released in
small amounts into the blood.
• Sex hormones stimulate the maturation of
gametes and may cause changes in color,
shape, and behavior before breeding.
• The release of these hormones is triggered
by environmental factors such as day length,
temperature, and the availability of food.
Reproductive System - Hermaphrodites
• A few marine fishes are hermaphrodites.
• Some are called simultaneous
hermaphrodites because they can produce
sperm and eggs at the same time.
– They are able to fertilize their own eggs.
However, they usually breed with one or more
other individuals.
• Hermaphroditism is found more commonly
among deep-water fishes, an adaptation to
the depths of the ocean where it may be
difficult to find members of the opposite
sex.
Black Hamlet
Barred Hamlet
Butter Hamlet
Indigo Hamlet
Reproductive System - Hermaphrodites
• Another variation of hermaphroditism is
called sex reversal, or sequential
hermaphroditism.
– In this case, individuals begin life as males, but
change into females (protandry), or females
change into males (protogyny)
– These changes are controlled by sex hormones
but triggered by social cues such as the absence
of a dominant male.
– Commonly occurs in sea basses, groupers,
parrotfishes, and wrasses.
Parrotfish
Red Grouper
Velvet Wrass
Giant Black Sea Bass
Reproductive Behaviors
• Many species migrate and congregate in specific
breeding grounds.
• Many bony fishes change color to advertise their
readiness to breed.
• Other physical changes may occur during mating
season.
– Male sockeyes jaws grow into vicious-looking hooks
– Male salmon develop a large hump
• The first step in reproduction is courtship, a series of
behaviors that serve to attract mates.
– May involve an exchange of active displays such as
“dances,” special postures that display colors, and
swimming upside down.
• Each species is unique in its courtship behaviors –
prevents breeding between two different species.
Reproduction – Internal Fertilization
• Some fishes have internal fertilization of the
eggs, in which the sperm is directly transferred
from males to females through the act of
copulation.
• Internal fertilization occurs mainly is
cartilaginous fishes.
• Not much is known about internal fertilization
and the sex life of these fishes.
• Male sharks, rays, and skates have a pair of
copulatory organs called claspers located along
the inner edge of the pelvic fins. Claspers are
inserted into the female’s cloaca.
Claspers
Reproduction – External Fertilization
• External fertilization, the release of gametes into the water,
or broadcast spawning, is more common in fishes.
• Open-water fishes and those living around coral reefs and
other inshore environments spawn directly into the water
after courtship.
• Females typically release many eggs
– Atlantic Cod – 1 m long female can release up to 5 million eggs
– Atlantic Tarpon – releases more than 100 million eggs every
time it spawns.
• Some eggs fertilized in the water column drift in currents
and develop as part of the plankton. Others eggs sink to
the bottom. Other fish deposit their eggs on the surface of
sea grasses, sea weeds, and rocks. Others bury their eggs.
Reproduction – External Fertilization
• Most of the eggs that are released into the plankton don’t
survive.
• Fishes that release eggs release as many as possible to
ensure that at least a few survive and make it to adulthood.
• Eggs require a lot of energy to produce because they must
contain enough yolk to nourish the young until they hatch
and can feed.
Damselfish Eggs
Do Any Fish Actually Take Care Of
Their Eggs?
• Fishes that spawn fewer and larger eggs have
evolved ways to take care of them.
• Damselfish – Males establish and defend
breeding sites or nests in holes among rocks or
coral, empty mollusc shells, an other shelters.
• Others that guard are gobies, blennies, and
scuplins.
• Antarctic Plunderfish – the female prepares a
breeding site and guards it for four to five
months after spawning. If she disappears or is
removed, her job is taken over by a male.
Male
damselfish
guarding his
nest
Antarctic plunderfish
Do Any Fish Actually Take Care Of
Their Eggs?
• Some fishes even carry their eggs after they
have been fertilized.
• Male pipefishes carry the eggs attached in
neat rows to their belly.
• A male seahorse literally becomes pregnant
after the female deposits eggs in a special
pouch on his belly!
• In some cardinalfishes, marine catfishes, and
other groups, males carry the fertilized eggs
in their mouths.
Male pipefish
with a very full
egg sac
Bigbelly seahorse
- pregnant male
Spiny Seadragon
Early Development – Oviparous Fish
• Most fishes spawn eggs and are known as
oviparous.
– The embryo is enclosed by a large, leathery egg case
that drops to the bottom after spawning.
– Some sharks, skates, and other cartilaginous fish are
oviparous – about 43%
– The egg cases are rather large and often have thin
extensions that attach them to surfaces.
– The eggs have a large amount of yolk in a yolk sac
that is attached to the embryo’s belly. Yolk provides
energy for several months of development.
– Results in a well developed pup when the egg finally
hatches.
Fish
Eggs
Horn Shark
Port Jackson Shark
Ghost Shark
Bamboo Shark
Zebra Shark
Swell Shark
Early Development - Ovoviviparous
• In ovoviviparous fish, the female retains the
eggs inside her reproductive tract for additional
protection.
– The eggs develop inside the female, which gives
birth to live young.
– Most of these fish are cartilaginous, with only a few
being bony fish.
– In some sharks, the embryos rely on other sources
of nutrition once they have consumed the yolk.
– Sandtiger shark – Only two pups, which are large (1
m) and active, are born. Each survived in one of the
two branches of its mother’s reproductive tract by
eating its brothers and sisters.
Ovoviviparous eggs
Porbeagle Shark Embryo
Dogfish Shark Embryo
Early Development - Viviparous
• In viviparous fish, embryos actually absorb
nutrients from the walls of the mother’s
reproductive tract.
– This is very similar to the development of the
embryo in mammals.
– Includes some sharks and rays. A few bony fish are
also included.
– These fish bear live young that got their nutrition for
development from direct contact with the
reproductive tract of the mother.
– The young have large fins that absorb nutrients
from the walls of the mother’s uterus.
Lemon Shark Embryo
Early Development – Bony Fish
• Development of the embryo proceeds rather
quickly in most bony fishes.
• The transparent outer envelope of the eggs,
the chorion, in thin, allowing oxygen to diffuse
through.
• The embryo is supplied with nutrient-rich yolk.
• After one or more days of development, the
eggs hatch into free-swimming larvae, or fry.
• When they first hatch, the larvae still carry the
yolk in a yolk sac.
• The yolk is eventually consumed, and the larvae
begin feeding.
Fun Videos - Pufferfish
• Pufferfish vs. Otter http://www.youtube.com/watch?v=OkXhC7y
zISI&feature=player_embedded
• Pufferfish Puffing http://www.youtube.com/watch?v=rAGWO5i
2C5M
Fun Facts: How do Pufferfish Puff?
• Pufferfish actually inflate themselves by
swallowing a bunch of water. The water is
then released when danger goes away.
• They can also inflate themselves with air
when out of water, but this air is harder for
the pufferfish to release. This may cause the
pufferfish to die.
Fun Facts: How do electric eels make
electricity?
• Electric eels have special muscle cells called
electroplaques.
• These electroplaques work like batteries and
are lined up along the entire body. They are
actually a modification of the lateral line.
• When needed, the eel can fire up each and
every electroplaque at the same time.
• The electric eel can produce up to 600V in a
single dischange -- this is 5 times the shock you
would get from sticking your finger into an
electrical socket.
Who is the most poisonous?
• The Reef Stonefish, Synanceia verrucosa, is
the most venomous fish in the world.
Who is the fastest?
• Most sources believe that the fastest species of
fish is the Indo-Pacific Sailfish, Istiophorus
platypterus.
• It has been clocked in excess of 110 km/h (68 mph)
over short periods.
Cool Fish Videos
• Fish spawning –
http://www.youtube.com/watch?v=xpxQN0DIcOE
• The Mola Mola fish http://www.youtube.com/watch?v=U60obmWODLQ
• Seahorse giving birth http://www.youtube.com/watch?v=MsHCqrrU-Gk
• Mouth Brooding Fish http://www.youtube.com/watch?v=LBzirqiU_uw
http://www.youtube.com/watch?v=bZ6-2zzFxeU
• Shark giving birth http://www.youtube.com/watch?v=zJbKbwuXij4