Dealing
with Delayed Mortality - It’s all About Oxygen
By Adam Johnson
Fighting,
handling and holding fish in captivity place severe metabolic
demands on brain, muscle, heart, gill and other organ tissues
putting them at considerable physiological risk. In general
terms we call this stress.
The degree of
stress fish realize, and the potential for subsequent recovery,
depends on the type and duration of the physiological stress we
place them in and the environment in which they are allowed to
recover.
Freshwater
fish rely heavily on oxygen in their environment. This oxygen
is used, primarily, to help fuel the biochemical mechanisms
associated with the energy recycling processes.
Oxygen-associated energy metabolism is highly efficient, and
produces the constant supply of energy that fish (or people, for
that matter) rely upon to support basically all physiological
functions. As long as oxygen and food (fuel) are readily
available, the recycling of energy continues unimpeded and the
energy supply meets demand. Fish must rely on constant supplies
of energy. And to get the energy they need, fish also must rely
on constant and plentiful supplies of oxygen. Lack of oxygen
will quickly deprive fish of the energy they need to sustain
life.
Fish can swim
continuously for long distances without tiring at a broad range
of speeds. This type of swimming, called “steady state
swimming,” is used by fish during normal cruising, or for
long distance travel. Muscles that are used in this type of
exercise use high volumes of oxygen for energy synthesis. As
long as there is a constant supply of oxygen, fish basically
never become tired during this type of exercise.
Sudden bursts
of high-intensity swimming are called “burst swimming.”
This type of swimming normally lasts for only seconds (possibly
minutes) and ends in a physical state of exhaustion. Burst
swimming is critical when fish attack prey, when they migrate
against strong currents or up waterfalls, or when they are
fighting after being hooked. This high-intensity exercise
totally drains fish of energy reserves. Recovery from such
exhaustive exercise may take hours, or sometimes days, depending
on the availability of oxygen following the exercise, the
duration of the exercise and the degree to which energy
compounds are consumed by, or lost from, the fish’s tissue.
Energy metabolism during burst swimming is anaerobic, providing
only enough energy for a few seconds. If the exercise
continues, tissue energy stores will become completely drained.
Think of this
in terms of a sprint-type exercise over a 100-yard dash. When
you sprint, your leg muscles totally consume their energy in
only seconds. Short rest between sprints allows the muscle to
restore a small amount of energy, but the next sprint is harder
and slower. With continued exercise, sprinting becomes
continually difficult until the muscle is totally exhausted and
you cannot run another step. Muscles become weak and spongy,
and if you are not used to the exercise they will be sore for
several days. Only the oxygen you breath after the exercise
will allow the energy in your leg muscles to recover, reducing
the soreness and regaining muscle strength. Imagine trying to
recover if a plastic bag was pulled over your head!
Now relate
this example to a fish involving its entire body in an
all-consuming sprint-type exercise lasting 30-seconds, two
minutes, or longer. Energy from the whole body is recruited and
used up. Even in a well-oxygenated environment, like a trout
stream, the fish will need to find a quiet place to rest for
several hours before it regains its energy. Imagine this fish
placed in a livewell with little or no oxygen. Energy cannot
recover and the fish will either die, or become so energy
starved it will likely die later. It is not the lack of oxygen
that kills the fish. It is the lack of energy and the inability
to recover lost energy stores.
In fish that
have been stressed by sudden bursts of high-intensity exercise –
like fighting at the end of a line – energy deprivation is the
most vital concern. Tissues become almost totally depleted of
energy, and it takes several hours (or perhaps days) for them to
recover. Anaerobic energy metabolism cannot keep pace with
cellular demand and large amounts of oxygen are needed to drive
the pathways of energy recovery in the cell. Oxygen deprivation
will not allow these pathways to function efficiently, if at
all. And the result is dead fish. They might not die right
away, but they will die.
Standard
livewell aeration systems simply cannot keep up with this oxygen
demand. A recirculating aeration system will raise the oxygen
level in a 15-gallon livewell from 3 ppm to 7 ppm in about eight
minutes when the water is 60 degrees. It will take about 14
minutes at 70 degrees. At 85 degrees, a standard livewell
system simply cannot get to 7 ppm. With several fish in the
livewell, a standard livewell system is not able to keep the
oxygen level above stressful limits that may prove fatal, or
will certainly create stress on the fish that may not be
recoverable – almost certainly leading to delayed fish
mortality.
Decreasing
the water temperature with ice is one solution, but remember
that too great a change in water temperature adds its own
element of stress. Large changes in water temperature affect
lactic acid clearance and slow metabolic recovery. In addition,
to lower the water temperature by five degrees for a full day in
temperatures above 85 degrees could require up to 50-pounds of
ice! Relying on ice to sufficiently cool a livewell to fully
oxygenate the water is unrealistic.
Supplemental
oxygen is required to supply fish the oxygen they need to
recover from metabolic stress and promote osmoregulation. There
are no two ways about it; oxygen delivery is the key to helping
fish overcome the stress that comes with angling and survival in
the livewell.
Adam Johnson
is a pro-angler and an Aquatic Biologist. His previous insights
into keeping fish alive were condensed from a report he
delivered at the 2004 Association of Great Lakes Writers (AGLOW)
conference. To view the entire report visit his web site at
www.adamjohnsonoutdoors.com
