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are compressed laterally. Still, within all this diversity, the general trend is for
fish to remain streamlined in shape. There are, as ever, some exceptions to
the rule. Some fish do not conform to a streamlined shape. Perhaps there are
no better examples of nonconformity than the seahorse and the sea dragon.
Some fish have very flexible bodies that enable them to turn in very confined
spaces; other have rather stiff and rigid bodies. The variations in body shape
along with fin configuration, as well as the number and shape of fins, affect
a fish's behavior, maneuverability, and speed. The diversity of body shape is
most evident among the numerous inhabitants of tropical reefs and in large
tropical rivers, though these variations are not restricted to one particular
environment.
FIG 4.67
Fish have different
body shapes, resulting in different
swimming gaits.
The bream
Bramis brahma
has a very deep body shape though it is rather
narrow. Its fins are suited to maneuverability rather than high speeds. Its
overall shape illustrates its preference to group together in large numbers and
graze along the bottom of lakes, ponds, or slow-flowing rivers and streams.
The trout
Salmo trutta
is long, thin, and very streamlined and perhaps
represents a stereotypical image of a fish. It has a shape that makes it much
more suited to colonizing fast-flowing water. The large fins and streamlined
profile enable it to hold station in the faster flow of small upland streams.
The eel
Anguila anguila
is elongated with one continuous fin extending halfway
along the top of the body. The eel's unique shape allows for an undulating
action, providing an ability to swim equally well both forward and backward.
