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Critters of the Chesapeake BayFishes
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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 FishesPropulsion 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 ShapesThere are four basic body shapes with all kinds of
variation in between.
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CompressedCompressed fish look like they have been smashed on
both sides.
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DepressedDepressed fish look like they were smashed from the top
and bottom.
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Terete or RoundThese fishes are round like a pipe. Most eels are
in this group.
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Fusiform or TeardropThis one we already mentioned. Typical of
the faster fish species.
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ScalesActually, not all fish have scales. Lampreys and
freshwater catfish lack scales. The American eel actually has small
scales. There are four basic types that well 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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CirculationThe 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
