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Zoology
Chapter 18
The Fishes
Introduction
• 70% covered in water
• living tissue mostly water
• adaptive radiation – formation of new
forms from a ancestral species usually in
response to new habitats
• craniata – skull that surrounds the brain,
olfactory organs, eyes and inner ear
• 1st found in a lancelet like animal 530
million years ago
• some found with teeth
Ostracoderms
• – bony armor group of fish, inactive
filter feeders (extinct) (armor as
only defense)
– no jaw or paired appendages
• Agnatha – no longer exists – used
to differentiate between absence of
jaw – except lampreys – more in
common with cartilaginous fish and
bony fish than the hagfish
– 41% of all fish species
live in freshwater
(.0093% by volume on
earth’s surface)
• The earliest known vertebrates with bone were a
diverse group of jawless fish known as
ostracoderms. These were armored animals
with internal skeletons of cartilage. All other
vertebrates evolved from them.
The three classes of ostracoderms appeared in the early Silurian and were
quite successful well into the Devonian. They had a lateral line system, an inner
ear with two semicircular canals, and bones in their external armor. It has been
suggested that the armor provided protection from large predatory arthropods
like the one in this illustration. Today the only surviving agnathans are the
lamprey and hagfish.
Survey of fish
• Subphylum Hyperotreti – Hagfish
– Class myxini
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•
•
•
•
•
Lack vertebrae – notochord as support structure
4 pairs of sensory tentacles surrounding their mouths
slime glands – produce slime
cold water marine habitats
most primitive group of craniates
live buried in the sand and mud
feed on soft bodied invertebrates, dead decaying fish
will find a fish enter through it’s mouth and eat leaving a
sack of skin and bones
• eat hook, swallow all way to anus, cause fisherman to cut
line
• skin is sold as eel skin
Jawless Fish
• Hagfish
Hagfish a. famous for the mass amounts of slime almost instantly secreted
as a defense mechanism.
• The internal anatomy of a hagfish includes a notochord that
persists into adulthood. A single individual has both ovaries and
testes, but only one is functional at any time. The eggs are
large and no larval stage has been found, although little is
known of reproduction in these animals. They produce copious
amounts of slime and can tie themselves into knots to escape
predators or obtain leverage while feeding.
Subphylum Vertebrata
– Ostracoderms, lampreys and gnathostome fishes
• Class Cephalaspidomorphi – lampreys
– Adults prey on other fish
– Larvae are filter feeders
– sucker like mouth
– sensory sensor lips
– use tongue to rasp away scales
– anticoagulant and feed on blood
– some not predatory
– reproduce then die shortly after, will travel miles to
spawn
– male and female wrap around each other for mating
– external fertilization
Jawless fish!
Lamprey
Evolution of Jaws
A major advance occurred with the evolution of jaws
from anterior gill supports
Gnathostomata
• jaws of vertebra developed from the most anterior pair
of pharyngeal arches – skeletal supports for the
pharyngeal slits
• gill ventilation and food capture
• paired appendages – allow for stability
• 2 classes
–
–
–
–
chondrichthyes – cartilaginous fish
osteichthyes – bony
most carnivores, or scanvengers
placoid scales – allows for reduction of friction within the
water, dried shark skin used for sand paper
Placoderms (Class Placodermi) are among the earliest known
gnathostomes or jawed vertebrates. These armored fish were first
found in the Silurian Period and flourished during the Devonian.
They were diverse in size and feeding habits. Some reached 10 m
in length and were active predators. Others had the flattened form
of bottom dwellers. They are not believed to be ancestral to any
living vertebrates and were all extinct by the Carboniferous.
• The Class Acanthodii, the
other group of early
gnathostomes, first appeared
in the Silurian and persisted
until the Permian. In this
group the external bony
armor was reduced to small
plates on the head and
scales on the rest of the
body. Acanthodians were
characterized by numerous
spines, at least some of
which supported fins, along
the top and sides of the
body. Most were small,
streamlined fish with large
eyes. Their relationship to
other fish is uncertain; they
have been placed with both
Chondrichthyes and
Osteichthyes.
Chondrichthyes – sharks, skates,
rays, ratfish
• SPOTTED RATFISH - Hydrolagus colliei
SPOTTED RATFISH
THORNBACK SKATE - Raja
clavata
Manta Rays
Differences between Skates and
Rays??
• Reproduction
– Rays are viviparous (bearing live young)
– Skates are oviparous (laying eggs)
Placoid Scales
Placoid Scales
• cartilaginous skeleton
• no swimbladder to regulate bouancy to
compensate has 1/3 of weight is liver and
oil which gives it bouancy
• sharks teeth are modified placoid scales,
outer wear out new teeth move in
• in young sharks teeth replacement is
within 7 to 8 days
• types of teeth depend upon what they eat
• Venice Florida - Shark and Sharks' Teeth
Information
sand tiger shark teeth
mainly grey shark teeth
cowshark teeth
• Cow sharks are a
primitive type of
shark. Whenever a
sevengill shark is
caught at a pier it is
usually the topic of
conversation. They
are fairly
uncommon at piers
and are about the
largest shark most
pier anglers will
encounter. A 7-footlong sevengill
shark, estimated to
weigh 180-185
pounds, was landed
at the Cayucos Pier
in November of
1998..
Cow Shark
Cow sharks (Hexanchidae) are a family of
sharks characterized by extra pairs of gill slits.
There are probably only two seven-gilled genera
• Some of the larger species of sharks are shown here. The
whale shark may reach 12 m in length and is the world’s largest
fish. It is a filter feeder, using its gills to strain plankton. Marine
sharks have body fluids at the same concentration as seawater
because they allow urea, a nitrogenous waste product, to
accumulate rather than excrete it immediately.
• size less than 1 m to greater than 10
meters
• largest sharks are filter feeders
• most feared great white extinct lengths
15 m
25 feet.
The Great White Shark
ovoviviparous (some do lay eggs)
gill slits, no
operculum
Female shark reproduction
Male Shark Reproduction
Male
• anal fin - the fin on the
• first dorsal fin - the fin
lower side of the body
on the upper side of the
near the tail (not on all
body nearest the head
sharks)
• gills - fleshy organs that
• caudal fin - the tail fin
are used for breathing they are located on the
• eye - sight organs
side of the head
located on the head
• mouth - the part of the
• fin spine - a protective
body which the fish uses
spine located at the base
to catch food - it is
of the first dorsal fin (not
located at the front of the
all sharks have fin
body
spines)
• nostril - paired slits on the underside of the
snout. Water continually flows through the
nostrils, giving the shark olfactory (sense of
smell) information. Unlike humans, shark nostrils
have nothing to do with breathing - they are not
even connected to the mouth.
• pectoral fin - each of the paired fins on either
side of the body, near the head
• pelvic fin - each of the small, paired fins on the
lower rear side of the body
• second dorsal fin - the fin on the upper side of
the body nearest the tail
• snout - the front part of the shark's head
• ventral fin - each of the paired fins on the lower
side of the body, near the head
Shark Power
Point
• THE SHARK
Goblin shark
goblin shark
Goblin/Frill sharks
Epaulette Shark
• Walks along sea
bottom
Epaulette Shark
Hammerhead shark
Helicoprion
Helicoprion
skeleton of a Megalodon
• range from 4050 feet (about
12-15 metres)
Previous much
larger
reconstructions
of the shark's
size, up to
about 100 feet
(30 m), are
generally
considered
inaccurate
Cladoselache
Cookie Cutter Shark
Cookie Cutter Shark
Cookie Cutter Shark
Osteichthyes
• some bone in their skeleton and/or scales
• bony operculum covering gill opening
• lungs or a swim bladder
Osteichthyes
• Bony fish first appeared in the Silurian. They are thought to have a common
ancestor with acanthodians. They are characterized by overlapping scales
and a bony skeleton. An advanced bony fish, Class Osteichthyes, like the
one shown here, differs in a number of ways from sharks and primitive bony
fish. The spiracle is gone, pelvic fins have moved forward, the tail is
symmetrical. As in chimaeras, the gills are covered by an operculum.
Osteichthyes is the largest class of vertebrates with over 20,000 species.
Subclass Sarcopterygii
lungfish – lungs for gas exchange
 when lakes and rivers become stagnate
these fish use lungs to breathe aire when
river beds dry up
 can hibernate or lay dormant for six
months or more
 will burrow in earth
 they will come out when it rains or river
starts to flow

Lungfish
Coelancanths
• – most recent fossil 70
•
•
million years old
1938, fishing, fish was
identified as coelancanths
– latineria chalumnae
80kg
1977 Latineria
menadoensis
• Latimeria chalumnae
is a lobed-finned fish
that was thought to be
extinct for over 60
million years.
• It is 5 feet in length,
weighs approximately 80
kg, has color ranging
from brown to dark blue,
and body patterns are
unique to the individual.
Coelacanths,
opportunistic predators,
feed by standing on their
head, swim backwards,
and belly-up using their
rosteral gland to locate
their prey. Then it sucks
its food into its hinged
jaws.
Coelancanths
Coelancanths
Picture of first coelacanth
discovered (1938).
Osteolepiforms – extinct
Subclass Actinopterygii
• ray finned fish
– fins lack
muscular
lobes
• usually
posses
swimbladders
– regulate
buoyancy
Chondrosteans
– most bony but
cartilaginous
– sturgeons and
paddlefish
• valued for
their eggs
• Most chondrostean species lived
during the late Palaeozoic. There
are only two chondrostean lineages
that survive today, the paddlefish of
Canada and China and the
sturgeons of Europe, Asia and
Canada.
• Both lineages have secondarily lost
a number of their actinopterygian
characters:
• scales lost on most of the body,
• cartilaginous skeleton,
• shark-like, heterocercal tail,
• rostrum extending past the mouth,
which forms the paddle of the
paddlefish.
• The earliest ray-finned fish were the chondrosteans, represented today only
by the few types of fish shown here. They retain primitive features including
thick scales, heterocercal tails and posteriorly placed pelvic fins. Most fish
today are the more advanced teleosts with thin scales, homocercal tails and
pelvic fins close to the anterior pectoral fins. Scales and tail types are
discussed in the next two screens.
• The scales of advanced bony fish are the vestiges of
the bony armor of their ancestors. They consist of a
thin layer of bone produced by the dermis of the skin.
The scales are covered by the thin epidermis.
• These are the types of caudal fins found in major
groups of fish.
Chondrosteans
• Paddlefish
• Lake Sturgeon
Neopterygii
– most living fish
are members
of this group
– lepisosteus,
garpike
– amia, dogfish
lepisosteus, garpike
Neopterygii
• Spiny dogfish
Evolutionary success
 highly efficient respiratory system allows fish to
extract oxygen from an environment that holds
little oxygen
 efficient locomotion structures allows fish to move
through a buoyant and high resistance to flow
 highly efficient sensory system, lateral line detects
low pressure waves and electro reception
 efficient reproductive mechanism huge number of
offspring
Evolutionary Pressure
 Locomotion
– stream lined
– mucoid secretion lubricates body to reduce
friction
– forked caudal fin used for speed
 Nutrition & Digestion
– larvae eat different than adult
– suction (close operculum open mouth)
Circulation & Gas Exchange
 closed circulatory system
 spiracles – water enters when mouth is
closed
 counter current exchange mechanism
 swimbladders and lungs
 Indian climbing perch – almost entire life on
land
– Pneumatic sacs functions as lungs
 Lungfish, ancients rhipidistians

The anatomy of
fish gills, with
many tiny folds
called lamellae,
greatly increases
the surface area
for gas exchange.
As blood flows
through capillaries
in the lamellae, it
moves in the
opposite direction
to the flow of
oxygen-rich water.
This greatly
increases the
amount of oxygen
the blood can pick
up by diffusion
Buoyancy
 we floated because air filled
lungs
 livers saturated with buoyant
oils
 use fins to provide lift
 reduction of heavy tissue
 swim bladder controls
volume of gas in its swim
bladder
Nervous & Sensory Functions




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brain and spinal cord
sensory receptors widely distributed throughout body
smell
eyes lidless and round
equilibrium, balance, hearing inner ears
Lateral line system – sensory pits in the epidermis of
the skin that connects to canals that run just below the
epidermis – receptors there stimulated by water
moving against them
– Used to detect water currents, predatory prey, low frequency
sounds
Electroreception & Electric fish
 Electroreception – highly developed in
sharks and rays
 Sharks have been known to find buried live
flounder but not dead ones because of the
electrical signals
 Electric fish generate electrical currents
 Electric eel – amazon shocks in excess of
500 volts

ELECTRIC
FISHES
STRONGLY ELECTRIC
SPECIES: marine electric
rays, freshwater African
catfish, freshwater electric
eel
WEAKLY ELECTRIC
SPECIES: freshwater
South American knifefish
and African elephant fish
ELECTRICALLY
SENSITIVE SPECIES:
Sharks, rays, skates and
catfish
Excretion and Osmoregulation
 Major function of the kidneys and gills of fish
 Excretory structures in the kidneys are called
nephrons, filter nigrogenous wastes, ions, water
 Freshwater fish never drink, and only take water in
when feeding this controls excess water buildup
and ion loss (osmotic uptake is across gills)
 Marine fish – they drink water and eliminate
excess ions by excretion, defecation, and active
transport across gill surfaces.
 Cloaca
Reproduction and Development
 45 kg of caviar from a single 450 kg sturgeon
imagine!!
 Most will not survive to reproduce
 Many eggs won’t be fertilized, washed up on shore,
dried, predation
 Ways to increase chances of survival
– Lay lots of eggs
– Mating behavior, ensures fertilization, nesting
 Reproduce in schools
 Most fish are Oviparous (eggs)
 Elasmobranches – ovoviviparous – embryos develop
in a modified oviduct of the female
Artificial reproduction of trout
Ovules are being obtained through
abdominal pressure
Weird Fish Facts
 Most lipstick contains fish scales.

The ocean floor is completely dark. Very few
fish can live there. The black angler fish is
one that does. It carries its own lantern to
lure Prey into its huge mouth. Bacteria that
glow in the dark make the light
Seahorse-Weedy Dragon
Alligator
Seahorse
Potbelly Seahorse
Leafy Dragon
Catfish
Flounder
 The summer flounder is a
member of the family,
Paralichthyidae. This lefteyed flatfish has both eyes
on the left side of its body
when viewed from above
with the dorsal, or top fin,
up. The eyed side of this
fish is scattered with 10 to
14 eye-like spots which
blend in with the ocean
floor, while its belly or
underside is white.
Flounder
Flounder
Halibut
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