Graphics Reference
In-Depth Information
its flukes to generate thrust and the way a tuna swims. They both drive the
hydrofoil through a relatively slender caudal peduncle, the whale beating its
flukes up and down while the tuna beats its tail from side to side.
Whales, dolphin, and tuna all use their hydrofoils in the same manner with
a relatively rigid body. The model that describes an action achieving equal
thrust on the up- and the downstroke holds true in these cases.
There is some evidence that swimming with limbs as hydrofoils may provide
a more efficient mode of locomotion than swimming with limbs as oars.
However, research has demonstrated that thrust with oars offers better
acceleration and enables better turning and breaking, and though hydrofoils
may be more efficient in power output, oars offer better maneuverability.
Many fish tend to use a mixed economy when it comes to the use of their
paired pectoral fins, sometimes using them as oars and at other times opting
for a hydrofoil action. In slower actions it may be possible to distinguish an
oar-like dynamic, but it is not always clearly evident when fish choose to use
their fins as oars or hydrofoils.
Swimming with Tails
As we have seen, the power for swimming comes from two distinctly different
kinds of muscle: fast red muscle fiber capable of generating short periods of
very high speed and slow white muscle fiber capable of maintain cruising
speeds over extended periods. The process of swimming with tails may use
both sets of muscles.
Swimming powered by the use of a tail is perhaps the most typical of all gaits
for fish locomotion. In very general terms, fish that use their tails for power
swimming keep their bodies fairly rigid, though this does not mean that
they are inflexible. Tuna have exceptionally rigid bodies and they depend
on being driven forward by their tails via the strong tendons within their
very slender and highly flexible caudal peduncles. The amplitude of the tail
beat in swimming fish, except at very low speeds, during which it may drop
significantly or stop altogether, remains fairly consistent, but this does vary
from species to species. At much slower speeds some fish drive themselves
forward by the use of pectoral fins, as we'll see in a moment.
To achieve swimming speeds from a standing start to a cruising speed, a fish
will increase the size of its tail beat. As swimming speeds continue to increase,
the size (amplitude) of the tail beat does not continue beyond a certain point.
Instead the increase of speed is achieved by increasing the frequency of the
tail beats. The tail does not move a greater distance; the fish simply moves it
faster and more often.
Swimming by Undulation
As we have already seen, fish that use their tails to swim generally maintain
a fairly rigid body posture. The tuna provides us with an illustration of a
fairly typical fish that depends principally on its tail action for swimming.
