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very same terms. The various types and orientations of movement may be
described as roll, yaw, and pitch, depending on the axis along which the
rotation takes place.
Roll
A roll describes a rotation along the length of the body longitudinally along
the anteroposterior axis, creating alternate upward and downward movement
of each flank of the fish.
Yaw
Yaw describes a rotation at the center of the fish along the dorsoventral axis,
creating a sideways action of the fish moving laterally from left to right.
Pitch
Pitch describes a rotation at the center of the body along the lateral, left/right,
axis, creating an alternating rising and falling movement of the fish's head
and tail.
Fish vary a great deal in shape, but they do share common features such as
the notochord, gills for the extraction of oxygen from water, scales (though
not all fish are scaled or fully scaled), and fins.
Fins are perhaps the single most defining feature of fish. Fish possess a
number of different types of fins, varied in shape and size from one species to
another. Though some fins have become highly specialized, they all by and
large serve the same purpose: to provide the fish with stability, lift, and the
means of locomotion.
There are paired fins that are capable of providing extreme maneuverability
and allow fish to undertake very precise and delicate actions. Sharks have
very stiffened paired pectoral fins made from cartilage; they are incapable
of being furled but provide the necessary lift to help sharks maintain their
depth in the water. Marlin pectoral fins are also stiff and strong and more than
capable of resisting the stresses that swimming at high speeds induces on
the fin. As with the shark, the marlin is not able to furl its fin, though unlike
the shark the marlin is able to fold the pectoral fins tight against the body to
assist in streamlining and reduce drag at very high speeds or when not in use.
Flying fish have developed especially long pectoral fins that, once unfurled
and extended, have an aerodynamic profile similar to that of a bird's wing that
enables the fish to glide over the water's surface.
The pike Esox lucius has developed fins located at the extreme end of its
streamlined body, allowing for high acceleration from the weed beds where it
spends much of its time in hiding, waiting for its prey to come within range.
The ways that body shape and in configuration have developed in
fish provide them with a morphology that allows them to thrive in the
environments in which they live.
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