Swimming fish
PHOTO: AFP
Swimming is an act that requires much energy. A fish swims
all the while without rest. How does it manage to do so?
G. VENKATARAMAN
Thanjavur, Tamil Nadu
True. Swimming is an act that requires a lot of energy
and that is why obese people are advised to swim besides
regular exercises. But it is not true that a fish swims all the
while without rest. In fact, it does not swim vigorously
unless alerted. It mostly rests in suspension or moves
occasionally but quietly. Such acts do not demand much
energy.
Energy is needed in an act, according to laws of physics,
only when such an act performs a finite amount of work
and work is said to have been accomplished only when a
body is displaced against some opposing force. A body
under equilibrium or in a state of suspension hardly does
any work or any work is done upon.
A normal fish has a unique anatomy that includes a gas
bladder or swim bladder which offers an ability to the fish
to control its buoyancy. The fish is, thus, able to stay in
suspension at any desired depth and ascend or descend in
quite pond water without having to spend much energy in
such acts. The only energy it needs in such controls is just
to inflate or deflate the gas bladder to the desired density
(buoyancy).
The wedge-like shape of the fish balances it from gravitational
pull while the mild jet power of the gills and the
paddling power of the pelvic and pectoral fins help it make
the gentle forward movement. The smoothness of the
scales gives minimal friction with water matrix. The dorsal,
fat and anal fins balance its body from toppling when
the caudal fin negotiates steering.
Only when the fish is in fast flowing water and when it
does not want to be carried along the flow or when it is
hunted by its predator, does it need to do a real swimming
(that needs to hold its own body relative to the frictional
force of the flow) and to spend some energy. It must have
that much energy lest it should be swept away along the
currents. For all these acts, the energy needed is not
astounding to fish' capability.
A. RAMACHANDRAIAH
Convener, Science Communication
Jana Vignana Vedika
Andhra Pradesh
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