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A General Look
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External Anatomy
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There are about 25,000 different
species of fishes. This is more than any
other vertebrate group.
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They come in all shapes and sizes.
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The largest is the whale shark.
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The abundance of fish life is a reflection of the abundance of plankton.
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Fish show almost infinite variety when it comes to color. They have
special skin cells called chromatophores.
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These chromatophores can expand or contract to change
the color of the fish.
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There are also many patterns. Many open water fish like this
tuna show countershading.
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They tend to be dark on top and light on the bottom.
Why do you think they have this pattern?
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Some fishes have a coloration pattern that allows them to blend
in to their environment.
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Some fish have very colorful warning coloration.
This is often used if they are poisonous, dangerous, or taste
bad.
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Many mid-depth fish are often red while lots of the deep water fish are
black and may have luminescent organs.
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Movement In Fishes
Propulsion in most fishes is
from the caudal fin and flexing the hind part of
the body.
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The faster swimming fish
also have a teardrop or
fusiform body shape to help them move through the
water.
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The dorsal and anal fins serve
primarily as rudders.
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The pectoral and pelvic fins are
used for balancing ,
turning, braking and going
backwards.
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Body Shapes
There are four basic body shapes with all kinds of variation in
between.
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Compressed
Compressed fish look like they
have been smashed on both sides.
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Depressed
Depressed fish look like they
were smashed from the top and bottom.
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Terete or Round
These fishes are round like a
pipe. Most eels are in this
group.
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Fusiform or Teardrop
This one we already
mentioned. Typical of the
faster fish species.
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Scales
Actually, not all fish have scales. Lampreys and freshwater catfish
lack scales. The American eel actually has small scales.
There are four basic types that we’ll look at today.
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Sharks and their relatives have placoid scales.
They feel a lot like sand paper.
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Gar fish, reedfishes, and
parts of sturgeons have a scale type known as rhombic
or ganoid.
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Ganoine gives them the “pearly”
look.
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Most bony fishes have
one or both of the next two
types.
The bony –ridge scales: cycloid and ctenoid.
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Cycloid are round and lack a “comb”
like edge.
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Ctenoid have the comb like edge. Scales can be over 7 inches!
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Circulation
The heart of a fish is simple when
compared to our heart.
They have a two cambered heart that follows a heart-gills-
body-heart path.
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Oxygen is then taken out of the water by the gills
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Internal Anatomy