Types of Fishes
Three types of fishes:
Jawless fishes
Cartilaginous fishes
Bony fishes
Jawless Fishes
• Class Agnatha
– Decendants of Ostracoderms (armored
fishes)
– Lack jaws, feed by suction with the aid of a
round, muscular mouth and rows of teeth
– Lack the paired fins and scales of most fishes
• Hagfishes, or slime eels, feed on dead or dying
fish
• Lampreys, primarily freshwater, some move to the
sea as adults. They attach to other fishes and
suck their blood or feed on bottom invertebrates
Cartilaginous Fishes
• Class Chondrichthyes
• Includes the sharks, rays, skates, and ratfishes
• Cartilaginous fishes have a skeleton made of
cartilage
• Cartilaginous fishes have rough, sandpaper-like
skin because of the presence of tiny scales,
which have the same composition as teeth
• Cartilaginous fishes have movable jaws and
paired fins
Sharks
• Sharks are adapted for fast swimming and
predatory feeding
• The tail,caudal fin,is well developed and
powerful. The upper lobe of the tail is
usually longer than the lower lobe.
Sharks Impact on Man
• Approximately 50 to 75 people are
attacked by sharks worldwide each year
Approximately 8 to 10 die due mainly to
loss of blood.
• This is less than the number of people
killed by bees, elephants, alligators,and
lightening
Man’s Impact on Sharks
• During the last few decades, commercial and
recreational shark fishing have increased
• The increase in commercial fishing is a result in the
increased demand for shark meat and fins
• The increase in recreational shark fishing is due in part
to the decline in numbers of other gamefish
• The combined effect of the increase in fishing by both
groups has led to a dramatic decline in large coastal
shark species
– The sandbar, blacktip, dusky, spinner, silky, bull, bignose, tiger,
sand tiger, lemon, night, nurse, great hammerhead, and
scalloped hammerhead
Fisheries management
• Plans have been developed and initiated
in some areas of the U.S. to counteract
the decline in shark species
Shark Attacks
• There are three sharks that have been identified
repeatedly in shark attacks
– The white shark
– The tiger shark
– The bull shark
• Most sharks have very specific diets and do not often stray
from these diets
• Sometimes man may look like a prey item to a shark (a surfer
may be mistaken for a seal or sea lion)
Phylogeny of sharks
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Kingdom – Animalia
Phylum – Chordata
Class – Chondrichthyes
Order – eight
Families – twenty nine
Species – over 350
Order
• Squatiformes (angel-fish sharks)
• Pristiophoriformes (saw carriers)
• Squaliformes (dogfish sharks) includes the smallest
shark – the spined pygmy
• Carcharhiniformes(jagged rasp)includes the
hammerheads
• Lamiformes – includes the megamouth, basking, white,
and thresher
• Orectolobiformes – includes the whale sharks
• Heterodontiformes (different teeth) includes bullhead
sharks
• Hexanchiformes – (six gilled sharks) the cow sharks
Morphology
• The skin – rough, covered with scales called dermal
denticles or placoid scales
• The fins – all sharks have one or two fins on the middorsal ridge called the first dorsal fin and the second
dorsal fin. These fins are used as anti-roll stabilizers.
– The pectoral fins are located behind the head and are used for
steering. They also provide lift (sharks tend to sink because they
lack a swim bladder)
– The paired pelvic fins are modified into organs known as
claspers
– One anal fin is located between the pelvic and caudal fins in
most sharks
– The caudal fin is used for propulsion and helps to lift the body
upward, providing some lift
Ampullae of Lorenzini
• Function as a sensory organ
• The ampullae detect electrical currents
(emitted by all living things) allowing the
shark to detect prey
• The ampullae are small sensory cells in
jelly filled canals located on the snout of
the shark
The eyes
• The eyes reflect light and are more
efficient in low light conditions
• Some sharks have a thickened eyelid
called a nictitating membrane which
protects the eye from injury when it is
about to bite its prey
Gill Slits
• All sharks have five to seven pairs of gill
slits that are external gill openings
• Water enters the mouth of the shark,
respiratory exchange of oxygen and
carbon dioxide take place on the gill
filaments, and excess water exits through
the gill slits
The Mouth
• Most sharks have jaws that can extend out
when the shark is biting its prey
• As the jaws recede back into the mouth,
the prey is forced down the esophagus
The Teeth
• Sharks’ teeth have evolved for cutting, seizing,
and crushing prey.
• The shape of the teeth are adapted for the
specific diet of the shark
• All sharks have from five to fifteen rows of teeth
• Teeth may be lost or damaged during the
feeding process. Lost or damaged teeth are
replaced after a few days from the row
immediately behind the functional teeth
The Lateral Line
• A series of fluid filled canals that lie just beneath
the skin on the sides of the shark’s body
• The lateral line functions in conjunction with the
inner ear and the ampullae of Lorenzini to detect
underwater sound and motion
• The lateral line allows sharks to orient and home
in on vibrations in the water (injured prey)
Reproduction
• All fertilization in sharks is internal
• There are three modes of reproduction
– Oviparity – the most primitive mode of reproduction found in the
bullhead sharks, the nurse sharks, and the catsharks
• Oviparous sharks lay eggs that contain an embryo that is in a
leathery egg case
– Ovoviviparity – the most common mode of reproduction in
sharks, the sharks grow in the uterus without forming a placental
connection with the mother.
– Vivaparity – the most advanced mode of reproduction, the
embryos of viviparous sharks are nourished by a placental
connection to the mother
Phylogeny of Bony Fishes
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Kingdom – Animalia
Phylum – Chordata
Orders –end in iformes
Families – over 500 end in dae
Class Osteichthyes
Approximately 23,700 species, over half of
all bony fishes live in the oceans
Morphology
• Fishes vary in shape but always have 3 major
parts: the head, the body, and the tail
• Usually have thin, flexible, overlapping scales
that develop from bone
• Fishes that are fast swimmers have a fusiform
body shape
• Counter shading is a type of coloration that
allows the fish to blend in with the surface when
viewed from below and to blend in with the
bottom when viewed from above
The head
• The head has the eyes, nostrils, mouth, and
gills.
• The area in front of the eyes above the mouth is
called the snout
• Bony fishes have 2 jaws
• The position of the mouth varies among species
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The mouth is terminal if it is at the tip of the head
The mouth is inferior if it is underneath the head
Superior if the lower jaw projects beyond the upper
Subterminal when the upper jaw projects beyond the
lower
The gills
• Fishes absorb oxygen from water, which is
taken in through the mouth, flows over the
gills and then passes out through the gill
openings
• A flap of bony plates and tissue known as
the operculum (gill cover), protects the
gills
Fins of Bony Fishes
• The fins consist of thin membranes that
are supported by fin rays (bony spines)
• The dorsal and anal fins are used as
rudders, to steer and provide stability
• The paired pelvic fins also help the fish
turn, balance and brake
• The caudal fin is almost always the same
size
The Mouth
• The mouth of most bony fishes is located
at the anterior end.
• Bony fishes have jaws with more freedom
of movement than those of sharks
• The teeth are fused to the jawbones
• Teeth can be replaced but new teeth do
not move forth in rows like in sharks
Swim Bladder
• Most bony fish have a swim bladder, a gas
filled sac just above the stomach and
intestine
• The swim bladder allows the fish to adjust
its buoyancy to keep from sinking or rising
• Many fish have special organs called the
gas gland and the rete mirabile that take
up gases for the swim bladder
Summary of Bony Fishes
• Bony fishes are the largest group of living
vertebrates
• have gills covered by an operculum
• have highly maneuverable fins
• have freely moveable jaws
• usually have a swim bladder
Biology of Fishes
• The scientific study of fishes is called
ichthyology
Body Shape
• The body shape of a fish is directly related to its
lifestyle and may be useful for camouflage
• Fast swimmers like sharks, tunas, mackerels
and marlins have a streamlined body shape that
helps them move through the water
• Flatfishes such as flounders, soles, and halibuts
are flat and adapted to live on the bottom.
– They lie on one side, with both eyes on top.
– They begin life with one eye on each side like other
fishes but as they develop one eye migrates up to lie
on the other side
Coloration- chromatophores
• Some bony fishes use color for camouflage
• Chromatophores – colored pigments
• The variation of colors and hues in marine fishes
results from combinations of chromatophores
with varying amounts of different pigment.
• Many fishes can rapidly change color by
contracting and expanding the pigment in the
chromatophores.
Coloration - iridophores
• Fishes also have structural colors that
result when a special surface reflects only
certain colors of light
• Most structural colors in fishes are the
result of crystals that act like tiny mirrors
– The crystals are contained in special
chromatophores called iridophores
– The iridescent, shiny quality of many fishes is
produced by structural colors in combination
with pigments
Warning coloration
• Color is used to indicate that the fish is
dangerous, poisonous, or tastes bad
Cryptic coloration
• Some fish are adapted to blend with the
environment
• Flatfishes, some blennies, sculpins, and
rockfishes can change color to match their
surroundings
Disruptive coloration
• Color stripes, bars, and spots help break
up the outline of a fish
– Disruptive coloration is common among coral
reef fishes
Countershading
• Open-water fishes and many shallowwater predators have silver or white bellies
and dark backs, this is a form of disguise
in open water
• When viewed from below, the light belly
blends with the bright light coming from
the surface.
• The dark back blends into the ocean’s
color when seen from above