TAKEOFF
BASS SCIENCE
ALL ABOUT THE SWIM BLADDER
I
HOW IT WORKS, AND HOW TO DEAL WITH BAROTRAUMA IN DEEP-CAUGHT FISH
f you go after bass holed up in deep water, you’ve likely
seen one you’ve caught roll on its side or back in your
livewell. Or perhaps you’ve released a bass only to watch
it struggle in its vain efforts to retreat back into the depths.
This phenomenon is caused by overinflation of the swim blad-
der, and if not dealt with properly can cause barotrauma,
By TJ Maglio
illustRations by Kevin hanD
which is any damage – even fatal – resulting from rapid pres-
sure change.
Although most anglers know that bass have swim bladders,
the function of the swim bladder and how it relates to fish care
are less understood. Further study of the swim bladder’s role in
bass biology can help anglers better care for their catch.
swim
bladder
stomach
What is It?
24
The swim bladder is a gas-
filled organ that allows fish to
adjust their buoyancy so they
can maintain their depth
without expending energy.
Think of the swim bladder as
a small balloon, which inflates
or deflates as the bass
changes depth. As a bass
moves up or down in the
water column, the swim blad-
der automatically adjusts the
volume of oxygen contained
to create neutral buoyancy. In
addition, the swim bladder is
located in a dorsal position
above the bass’s center of
gravity, which aids in stability.
Swim bladders are pres-
ent in almost all species of
bony fish and evolved from a
lung-like organ present in
early aquatic vertebrates. In
some freshwater species
such as gar and bowfin the
gonad
bladder
intestine
swim bladder actually pro-
vides a secondary method of
oxygen exchange in addition
to the gills. This is why gar
and bowfin can live in shal-
low backwaters with less oxy-
gen, and why anglers some-
times see them gulping air at
the surface.
how does it Work?
To inflate their swim blad-
ders, bass and many other
fishes have evolved a small
gas gland in the swim blad-
der’s wall where blood ves-
sels interface with the swim
bladder. To inflate, the gas
gland secretes lactic acid into
the adjacent blood vessels,
which builds up carbon diox-
ide and causes hemoglobin
in the vessels to dump oxy-
gen. The oxygen diffuses into
the swim bladder to inflate it.
There is another struc-
ture in the swim bladder
membrane called the “oval
window.” To deflate, oxygen
diffuses through this portion
of the wall and back into the
bloodstream.
Barotrauma
Pulling a bass from deep
water too quickly causes the
gasses in the swim bladder to
expand too rapidly, which can
cause physical damage (baro-
trauma) and even death. A
recent study found that some
bass began to show signs of
clinical barotrauma when
pulled to the surface from
simulated depths of just 12
feet. When pulled from 30
feet, bass were unable to
immediately resubmerge. At
35 feet, barotrauma was rou-
tinely severe, and in this case
mortality rates of up to 78
percent were recorded when
the water temperature was
higher than 80 degrees.
Studies have also indicat-
ed that water temperature
and species are key indica-
tors in the likelihood that a
deep-caught bass will experi-
ence barotrauma. In cold
water, bass are much more
resilient and less likely to
exhibit symptoms, and small-
mouth bass are more prone
to exhibit barotrauma than
largemouth bass and spot-
ted bass.
Anglers should either be
prepared to deal with this sit-
uation (see next page) when
fishing deep water, particu-
larly in summer, or reconsid-
er where and how they fish
to avoid unnecessary stress
on the bass.
FlWFIshIng.com I July 2017