Keeping your catch alive

Material Information

Keeping your catch alive
Translated Title:
Circular / Florida Cooperative Extension Service ; no. 691 ( English )
Schramm, Harold L.
Place of Publication:
Gainesville, Fla.
Florida Cooperative Extension Service, IFAS, University of Florida


Subjects / Keywords:
Water temperature ( jstor )
Fish ( jstor )
Oxygen ( jstor )

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University of Florida
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site maintained by the Florida
Cooperative Extension Service.

Copyright 2005, Board of Trustees, University
of Florida



Harold L. Schramm, Jr.

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Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean

Circular 691

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Harold L Schramm, Jr*

Millions of angler-days are spent annually fishing
for largemouth bass (Micropterus salmoides), and the
popularity of bass fishing continually increases. For
several reasons, such as keepingtheir catch fresh or for
live release after a tournament, many bass anglers try
to keep their catch alive.
The purpose of this publication is to provide infor-
mation to largemouth bass anglers that may aid in
keeping their catch alive. Although the problems and
solutions discussed here focus on largemouth bass, the
information can be readily applied to other warmwater
sport fishes.

Factors Affecting Mortality
Numerous factors affect the survival of largemouth
bass, such as disease and parasites, predation, tox-
icants and pollutants, and water quality of the lake or
river. The angler has little or no control over these fac-
tors. The angler can, however, affect the mortality of
the fish caught by the way the fish are handled and the
conditions in the boat livewell.
Hooking and Handling
Many studies conducted on the mortality of fish
caused by hooking and handling have shown that
mortality of fish caught and released immediately is
usually low. Some mortality is inevitable because
penetration and removal of the hook causes tissue
damage. The severity of the injury depends on where
the fish is hooked. Fighting a fish, landing it, and
removing the hook stresses the fish and necessitates
Water Temperature
Cold water temperatures have not been shown to be
stressful to the largemouth bass. Warm water tem-
peratures, however, can be stressful and lethal to
largemouth bass. Laboratory studies have shown that
the highest water temperature that allowed long-term
survival of the northern largemouth bass (Micropterus
salmoides salmoides) was about 98'F (37 C), and the
highest water temperature that allowed long-term
survival of the Florida largemouth bass (Micropterus
salmoides floridanus) was about 93F (32'C). Adult
largemouth bass in the wild typically avoid water
warmer than 860F; preferred water temperature is

Temperature "shock" (rapid temperature fluctua-
tions) can also cause mortality. There are two common
situations that can result in temperature shock of bass
in a livewell. First, there can be large differences in
water temperature between the livewell and the habi-
tat the fish occupied before it was caught. During
warm, calm weather, water temperature at the surface
of a lake can be 50F or more warmer than deeper water
or water in dense aquatic vegetation. Since water to fill
the livewell is taken from the surface of the lake, a bass
can be heat shocked by being put into a freshly-filled
livewell. Second, livewell water temperature can in-
crease quickly on a hot, sunny day. It is important to
recognize that rapid cooling of water in the livewell can
also cause temperature shock to the bass.
The effects of temperature increases depend on the
temperature of the water the bass occupied (referred to
as the acclimation temperature), how much the tem-
perature increases, and the length of exposure to the
elevated temperature. Laboratory trials (Table 1) in-
dicate several important effects of water temperature.
Temperatures below 90F have little effect on
largemouth bass caught from waters above 680F. Bass
caught in warmer waters can tolerate higher livewell
temperatures. Small temperature changes above 90F
in the livewell water can have large effects on the sur-
vival of largemouth bass.

Table 1. Time (hours) to 50% mortality for northern and
Florida largemouth bass.

Test temperature Acclimation temperature
oF (0F)
68 77 86
Northern largemouth bass
92 1
94 25
96 2
98 <1 15
100 2

Florida largemouth bass
90 17
92 2 13
94 3 23
96 1 8
98 3
100 <1

*Harold L. Schramm, Jr. is Assistant Professor and Fisheries Science Specialist, School of Forest Resources and Conservation, IFAS, University
of Florida, Gainesville.

Dissolved Oxygen
The amount of oxygen dissolved in water is express-
ed as parts per million (one ppm equals one unit weight
of oxygen in one million unit weights of water) or
milligrams per liter. Oxygen affects the behavior,
feeding rate, growth rate, and survival of largemouth
bass. Although inactive largemouth bass can tolerate
levels as low as 1 to 2 ppm, dissolved oxygen should be
above 5 ppm.
There are several important interactions between
dissolved oxygen and other factors. First, the oxygen in
a lake is produced by the photosynthetic activity of
plants (algae and vascular plants) in the light. In the
dark, these plants will consume oxygen. Therefore the
amount of oxygen in the water varies during a 24-hour
period. The amount of oxygen water will hold (the
saturation level) decreases as water temperature
increases (Table 2). Because fish are cold-blooded,
metabolism increases with water temperature. As
metabolism increases, oxygen requirements of the fish
increase. Therefore, a bass in warm water consumes
more oxygen than a bass in cooler water. As activity
increases, oxygen consumption also increases. Like an
athlete, hard "fighting" fish can develop an oxygen
debt; the fish must consume additional oxygen to
return to a stable metabolic level.

Table 2. Dissolved oxygen saturation concentrations at
different water temperatures.
Water temperature Dissolved oxygen
(F) (ppm)
60 9.6
70 8.7
80 7.9
85 7.6
90 7.3
95 7.0

Delayed Mortality
Although the factors discussed above can kill fish
in a few hours, stressful, but not immediately fatal,
levels of such factors as high water temperature, low
dissolved oxygen, and high dissolved wastes can cause
mortality of largemouth bass 1 day, 2 days, or even a
week after release. Therefore, it is important to main-
tain the best possible conditions in the livewell.

How to Keep the Fish Alive
Fishing magazines and books commonly cover the
subject of how to remove bass from the water, hold
bass, and remove hooks. Our recommendations are
simply to handle the fish as little as possible, remove

the hooks with minimum tissue damage, and return
the fish to good quality water as quickly as possible.
One common technique for holding bass is to grasp the
lower jaw and pull downward. This technique immobi-
lizes the fish and allows the angler to securely hold it.
For large bass, however, it is desirable to provide addi-
tional support by resting the body of the fish on
something or keeping it in the water while holding by
the lower jaw. Grasping a hook with pliers can often
result in quicker and less damaging hook removal
than can be accomplished by twisting and pulling on a
hook with your fingers. When a bass is hooked in such a
way that excessive tissue damage will result from
removing a hook, cut the hook with a wire cutter and
pull it through the tissue. If the hook cannot be pulled
through, (for example, when the fish is hooked deep in
the soft lining of the throat), cut the hook and leave it in
the tissue.

Building or Improving a Functional Livewell
The size (volume) and shape oflivewells vary among
different boats with built-in livewells. There is little an
angler can do to change the shape of the built-in live-
well; however, there are minor modifications that can
improve the livewell. The livewell must not drain
when the boat is underway. A removable plug is a sim-
ple solution to this problem. The inside of the livewell
should be smooth to reduce injury to the bass, and there
should be no features that allow a fish to become
trapped, such as an improperly placed pump, pipe, or
wires. A large water volume is desirable, and water
depth should be at least 10 inches. Putting a removable
plug in the overflow outlet can increase the depth and
volume of the livewell considerably.
All livewells should have two water circulation
systems: a way to supply water from the lake or river
(outside water) to the livewell and a way to recirculate
the water in the livewell. In all boats, outside water
either flows into the livewell by gravity or is pumped
into the livewell. Although intake pumps are conven-
ient, they are certainly not necessary. A bailing can or
similar device is adequate for filling a gravity-flow
livewell if additional water is needed. (A bailing can is
also useful for filling the livewell in the event of a pump
failure.) The intake opening on the outside of the boat
hull should be screened to prevent debris or aquatic
vegetation from clogging pumps and plumbing.
A livewell recirculation system is needed so that
aeration can be provided when the boat is under way.
For anglers fishing in warm waters (surface tempera-
ture higher than 86F), the recirculation system is the
aeration system. A livewell recirculation system also
allows the angler to control the water temperature and
water quality in the livewell. A recirculation system
can be easily installed at low cost. A submersible,

12-volt bilge pump with a capacity of 250-400 gallons
per hour provides a desirable water flow.
Choose a pump that allows easy separation of the
pump base from the motor housing so that the impeller
can be cleaned. Mount the pump base permanently to
the side of the livewell. Permanent mounting prevents
movement of the pump and subsequent mechanical
stress on electrical wires and plumbing. Mounting the
pump on the side of the livewell, above the livewell bot-
tom, minimizes uptake of debris (such as fish scales
and regurgitated food particles) that can clog the pump
or the plumbing. Plumbing materials and designs can
vary greatly and there are several important consid-
erations. Choose materials that are either stainless
steel or non-metallic. Use flexible tubingto connect the
pump to the aeration device so that the pump can be
quickly dissassembled for cleaning. Secure plumbing
and wires to the walls of the livewell. The aeration
device should provide a spray of water to insure ade-
quate aeration of the livewell water. A simple and very
efficient aeration device is a 1/2 or 3/4 inch PVC end
cap threaded or slip-fitted (not glued) to a section of 1/2
or 3/4 inch PVC pipe. Cut a notch into the end cap
(Figure 1) with a hacksaw. If the notch is properly cut
(this may take a little experimentation), this simple
aeration device will provide a strong, fan-shaped spray
of water. A relatively large notch is not as susceptible
to clogging as are many small holes drilled into a piece
of pipe. By threading or slip-fitting the end cap to the
PVC pipe, the end cap can be quickly removed for
cleaning when necessary.

Aeration nozzle made from a PVC end cap.

An auxiliary livewell can be easily constructed from
a cooler. A 48 to 70 quart cooler is a good size to use for
most applications. The smooth plastic inner walls will
not injure the fish and allow easy installation of the
recirculation system. Securely mount the recircula-
tion pump and plumbing with sheet metal screws and
silicone caulk. Solder the short electrical leads from
the pump to 16/2 or 18/2 Type S or SJ wire. Ring ter-
minals or alligator clips allow quick connection of the
power cable to a marine battery. If your boat is so
equipped, attaching a cigarette lighter plug to the
power cable allows the recirculation pump to be easily
turned on and off. An added benefit of using a cooler as

a livewell is that the insulation facilitates control of
water temperature. The converted cooler is also useful
as a portable bait well.
Timer systems for livewell recirculation pumps are
factory-installed on some boats or can be purchased
from fishing tackle or marine suppliers. These timers
reduce the power drain to the boat battery. To be used
effectively, however, they must be adjusted to insure
sufficient oxygenation of the livewell water. Even a
short exposure to oxygen-deficient water can result in
mortality of the fish.

Water Temperature
Livewell water temperatures can be lethal to fish,
but control of water temperature to minimize fish
mortality can be easily accomplished in a properly de-
signed livewell. In cool weather or when the water tem-
perature is cool, desirable livewell water temperature
can be maintained simply by the input of cool, fresh
water. Keep in mind that livewell water temperature
can increase on a cool day if the weather is clear and
sunny. Under such conditions, frequent inputs of cool,
fresh water may be necessary. Livewell water tem-
perature should not be more than 5F warmer than the
temperature of the water the fish occupied before it
was caught.
Temperature control in warm weather requires
more consideration. On a sunny, 90F day, the livewell
water temperature can rise to lethal levels. Water tem-
perature on the surface of the lake can also attain
temperatures of 90F or warmer. Therefore, pumping
lake water into the livewell will do little to lower the
livewell temperature and, in fact, may raise it. In
warm weather, livewell water temperature can be
maintained by adding ice to the livewell and using the
recirculation system to aerate the cool water. When
fishing in water with temperatures of 86F or warmer,
maintain livewell water temperature at 81-860F. Use
blocks of ice, rather than crushed or cube ice. The large
blocks of ice melt slowly and therefore cool the water
slowly and maintain a more stable water temperature.
Block ice can be economically made by freezing water-
filled half gallon plastic bottles (such as a milk jug). On
a hot summer day, 8 or 10 half gallon ice blocks may be
needed to maintain desirable water temperatures in
the livewell throughout the day.
Rapid water temperature fluctuations can be as
harmful to the largemouth bass as elevated tempera-
tures. If fresh water is added to the livewell, additional
ice may be necessary to adjust the temperature, espe-
cially if the surface water is 900F or warmer. Put the ice
in the livewell at the same time the warm water is add-
ed to prevent temperature fluctuations.

Dissolved Oxygen
Oxygen should be maintained at saturation. Unfor-
tunately, measurement of dissolved oxygen requires
expensive meters or laborious chemical analysis. One
way to estimate dissolved oxygen is to watch the fish.
When oxygen levels drop, the bass may become list-
less, rest at the surface, or lose equilibrium. These
behaviors indicate that the oxygen concentration has
already declined to stressfullevels. Restoring the oxy-
gen to satisfactory levels may revive the fish, but some
fish may die after release.
A well-designed recirculation system should main-
tain adequate dissolved oxygen in the livewell water if
the system is used properly and the livewell is not over-
crowded. Because warm water has a lower oxygen
saturation level than cool water and bass consume
more oxygen in warm water, more aeration is required
in warm water than in cool water. Cooling the water,
therefore, will facilitate maintaining desirable
dissolved oxygen levels. More aeration is required
when more pounds of fish are in the livewell. The
livewell is overcrowded when the fish impede the cir-
culation of the water.

Continuous operation of the recirculation (aeration)
system will not harm the fish if water temperature is
constant. In fact, continuous operation of the recircula-
tion system may be necessary if a large catch offish is
being held in the livewell.

Filling and Flushing the Livewell
Two important criteria for filling the livewell are 1)
to use clean water with good water quality, and 2) to
use water from the habitat where the fish are caught.
The use of water from the habitat where the fish are
caught is important because the chemical composition
of different water bodies can differ widely. Fish can ad-
just to these differences in water quality but should not
be "shocked." There is little need to be concerned about
differences in water quality from one end of a lake to
another. On the other hand, it is not desirable to hold
fish caught in one lake in water from another lake, nor
is it desirable to fill the livewell with well water or tap
Keep in mind that the "fresh" water put into a
livewell may not be suitable for keeping fish alive.
Assuming clean water is used to fill the livewell,

Schematic view of a livewell recirculation system

temperature and dissolved oxygen should be con-
sidered. For example, if the livewell is filled with lake
water on a warm, sunny afternoon, it is likely that the
water in the livewell will be warmer than the water
where the fish was caught. In this case, the water
temperature should be lowered. The oxygen concentra-
tion of lake water declines during the night. When a
livewell is filled with lake water at night or shortly
after sunrise, aeration should be started immediately
to add oxygen to the water.
The primary waste products of freshwater fish are
ammonia and carbon dioxide. These compounds are
dissolved in the water and are toxic to fish. It is ad-
visable to flush out waste products by supplying fresh
water to the livewell during a long fishing day. The
amount and frequency of fresh water additions will de-
pend on the number and size of the fish, the livewell
volume, and the temperature. As a rule of thumb, flush
the livewell every two hours if it contains one-half
pound of fish per gallon of water. At higher fish den-
sities, more frequent water changes are necessary.
Livewell Water Additives
Several brands of water additives have been
developed to promote the survival offish in livewells.
These formulations contain a variety of chemicals that
can reduce some fungal and bacterial infections and
sedate the fish. These compounds are available at most
fishing tackle suppliers. Dose rates are specified on the
label and should be followed. Fish culturists commonly
use salt to counteract stress when handling and trans-
porting fish. Sea salt is preferable; however, rock salt
or table salt works well. Dose rates are 0.5 1.0% (0.7 -
1.3 ounces of salt per gallon of water).
Proper use of formulated livewell additives or salt re-
quires knowledge of livewell volume. Furthermore,
because anglers will often add fresh water to the
livewell during a fishing day, the flushing rate of the
livewell should also be determined. Flushing rate is
difficult to determine because the angler must know
the input rate of fresh water. Difficulty in determining
the rate is further compounded because an input of five
gallons of fresh water does not automatically result in
the outflow of five gallons of "old" livewell water. A
simple way to maintain accurate concentrations of ad-
ditives is to drain or remove a known amount of water,
refill the livewell to the original level, and then add a
proper amount of additive.

Dead Fish

Even with proper and diligent care, occasionally
a bass will die in the livewell. Dead fish should be re-
moved from the livewell immediately.

Releasing Fish
Live fish should be released into good quality water.
Observations during our research on live release of
fish following bass tournaments indicate strong, non-
stressed bass may move great distances to desirable
habitats when released. On the other hand, stressed
bass may move to the nearest cover or simply rest on
the bottom. Since the stressed fish require the best
possible environmental conditions to recover and sur-
vive, they should be released into good quality water at
a location where they have access to well oxygenated,
relatively cool and deep water.

Fish should be handled as quickly and gently as
possible, and hooks should be removed with a
minimum of tissue damage.
Water temperature and dissolved oxygen level are
the most important factors affecting survival of large-
mouth bass in a livewell, but these factors can be easily
Since water quality in the livewell can deteriorate
and stress the fish, flushing the livewell with fresh,
clean water is desirable.
The techniques suggested in this publication will
minimize stress to fish in the livewell and maximize
the survival of the fish after they are released. It is im-
portant to recognize that the diligence of the angler is
the ultimate factor affecting the survival of his catch.
A large, well-designed livewell with a good recircula-
tion system and the use of"fish saving" chemicals will
not insure the survival of the fish without frequent
monitoring of the water temperature and the condition
of the catch.


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Coutant, C. C. 1975. Temperature selection by fish a factor in powerplant impact assessments. Pages 575-597 in The
International Atomic Energy Agency. Environmental effects of cooling systems at nuclear power plants.
Dotson, T. 1982. Mortalities in trout caused by gear type and angler-induced stress. North American Journal of Fisheries
Management 2:60-65.
Hart, J. S. 1952. Geographic variations in some physiological and morphological characters in certain freshwater fish.
University of Toronto, Biological Series No. 60.
Hunsaker, D., L. F. Marnell, and F. P. Sharpe. 1970. Hooking mortality of cutthroat trout at Yellowstone Lake. The Progressive
Fish Culturist 32:231-235.
Schramm, H. L. Jr., P. J. Haydt, and N. A. Bruno. 1985. Survival of tournament-caught largemouth bass in two Florida lakes.
North American Journal of Fisheries Management 5: in press.

This publication was promulgated at a cost of $1,110.00, or 24.7 cents per copy, to inform fresh water fishermen
in Florida about procedures for keeping fish alive for release or to preserve freshness. 8-4.5M-85

SCIENCES, K. R. Tefertlller, director, In cooperation with the United States Department of Agriculture, publishes this Infor-
mation to further the purpose of the May 8 and June 30, 1914 Acts of Congress;and Is authorized to provide research, educa- |
tional Information and other services only to individuals and institutions that function without regard to race, color, sex or
national origin. Single copies of Extension publications (excluding 4-H and Youth publications) are available free to Florida
residents from County Extension Offices. Information on bulk rates or copies for out-of-state purchasers Is available from
C. M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Galnesvllle, Florida 32611. Before publicizing this
publication, editors should contact this address to determine availability.