Biology
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30-2 Fishes
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What Is a Fish?
What Is a Fish?
Fishes are aquatic vertebrates. Most
fishes have paired fins, scales, and gills.
Caudal fin
Dorsal fin
Lateral line
Scales
Eye
Mouth
Anal fin
Pelvic fin
Pectoral fin
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Operculum
(gill cover)
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Evolution of Fishes
The First Fishes
The earliest fishes to appear in the fossil record
lived about 510 million years ago.
These fishes were jawless and had bodies
covered with bony plates.
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Evolution of Fishes
The Arrival of Jaws and Paired Fins
The evolution of jaws in fish was extremely useful.
Jaws with muscles and teeth made it possible for
fish to eat a wider variety of foods.
Animals with jaws can also defend themselves by
biting.
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Evolution of Fishes
The Rise of Modern Fishes
Early jawed fishes soon disappeared, but left
behind two major groups that continued to evolve
and still survive today.
One group—the ancestors of modern sharks and
rays—evolved a skeleton made of strong, resilient
cartilage.
The other group evolved skeletons made of true
bone.
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Form and Function in Fishes
Fishes use their gills to exchange gases by pulling
oxygen-rich water in through their mouths,
pumping it over their gill filaments, and pushing
oxygen-poor water out through openings in the
sides of the pharynx.
Gills
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Form and Function in Fishes
Circulation in a Fish
Gills
Body
muscle
circulation
Digestive system
circulation
Brain and
head
circulation
Heart
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Form and Function in Fishes
Many bony fishes have an internal, gas-filled organ
called a swim bladder that adjusts their buoyancy.
Swim bladder
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Groups of Fishes
Groups of Fishes
All living fishes can be classified into
three groups: jawless fishes,
cartilaginous fishes, and bony fishes.
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Groups of Fishes
Jawless Fishes
Jawless fishes have no true teeth or jaws.
Their skeletons are made of fibers and cartilage.
They lack vertebrae, and keep their notochords as
adults.
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Groups of Fishes
Modern jawless fishes are divided into two classes:
lampreys and hagfishes.
Lamprey
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Hagfish
Hagfish
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Groups of Fishes
Sharks and Their Relatives
The class Chondrichthyes contains sharks, rays,
skates, sawfishes, and chimaeras.
The skeletons of these fishes are built entirely
of cartilage.
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Pacific Manta Ray
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Groups of Fishes
Bony Fishes
Bony fishes make up the class Osteichthyes.
Their skeletons are made of bone.
Almost all living bony fishes are ray-finned fishes.
“Ray-finned” refers to the slender bony spines, or
rays, that are connected by a thin layer of skin to
form the fins.
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Bony Fish
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A characteristic of almost all fish is
a. a notocord as an adult.
b. the presence of scales.
c. a skeleton made of cartilage.
d. the lack of jaws.
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An example of a fish that is a filter feeder as a
larva and a parasite as an adult is a
a. shark.
b. skate.
c. lamprey.
d. lungfish.
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Most members of the class containing sharks
and rays are characterized by
a. a cartilaginous skeleton.
b. a bony skeleton.
c. a single operculum over the gills.
d. no swim bladder.
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