• TABLE OF CONTENTS
HIDE
 Front Cover
 Introduction
 Naturally occurring fish kills
 Low dissolved oxygen levels
 Spawning fatalities
 Mortality due to cold temperat...
 Stress in fish
 Diseases and parasites
 Toxic algae blooms
 Human induced fish kills
 What you can do if you observe...
 Collecting fish and water...
 Fish health diagnostic facilities...






Title: Beginner's guide to water management: fish kills
CITATION PAGE IMAGE PAGE TEXT
Full Citation
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Permanent Link: http://ufdc.ufl.edu/UF00055860/00001
 Material Information
Title: Beginner's guide to water management: fish kills
Series Title: Florida LAKEWATCH Information Circular 107
Alternate Title: Fish kills
Physical Description: Book
Language: English
Creator: Florida LAKEWATCH.
Affiliation: University of Florida -- Florida Cooperative Extension Service -- Institute of Food and Agricultural Sciences
Publisher: University of Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences
Publication Date: 2004
 Subjects
Spatial Coverage: North America -- United States of America -- Florida
 Record Information
Bibliographic ID: UF00055860
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: notis - ocm5486

Table of Contents
    Front Cover
        Page 1
    Introduction
        Page 2
    Naturally occurring fish kills
        Page 3
    Low dissolved oxygen levels
        Page 3
        Page 4
        Page 5
        Page 6
    Spawning fatalities
        Page 7
    Mortality due to cold temperatures
        Page 7
    Stress in fish
        Page 8
        Page 9
    Diseases and parasites
        Page 10
    Toxic algae blooms
        Page 11
    Human induced fish kills
        Page 12
        Page 13
    What you can do if you observe a fish kill
        Page 14
    Collecting fish and water samples
        Page 15
    Fish health diagnostic facilities in Florida
        Page 16
Full Text


M : A Begirer s ui.le I,, Valer !lanagemenl Fish i Kiii Inirmainaion C irullar 107




SI. .




fish kill is an event in which dead or dying fish are observed in a
Lake or waterbody. Some fish kill events involve small numbers
of fish and others may involve hundreds, or even thousands of fish.
There are many factors that can contribute to a fish kill. This
pamphlet was created to explain the most common factors and how they
affect Florida's freshwater systems. It includes discussion of both natural
and human-induced causes, as well the effects that stress can have on fish
a component of virtually every fish kill situation.
S-. We hope this information will provide a greater understanding of the
processes that commonly occur during a fish kill event, and perhaps
.. alleviate some of the concerns you may have.
Should a fish kill occur in your area, the last section of this pamphlet
(pages 14-16) provides steps you can take to help determine the cause.
~.R While this task can be challenging, the chances for success are greatly
increased if both fish samples and water samples can be collected from
the waterbody and analyzed in a timely manner. A listing of fish health
diagnostic laboratories is provided on page 16.* If too much time has
already passed or if you don't have time to submit samples, the observa-
tions you collect can still provide important clues about what may have
happened. Be sure to gather this information as soon as possible and
contact the appropriate agency, listed on page 14.
There are usually fees associated with having samples tested in a laboratory; it is recommended that
you call ahead and discuss the cost before going to the trouble of collectiu, and submitting samples.

Included in this pamphlet:

Introduction 2
Naturally Occurring Fish Kills 3
Low Dissolved Oxygen Levels 3
Spawning Fatalities 7
Mortality Due to Cold Temperatures 7
Sidebar: Stress in Fish 8
Diseases and Parasites 10
Toxic Algae Blooms 11
U.. NIVERSITY OF Human Induced Fish Kills 12
-,FLORIDA What You Can Do If You Observe a Fish Kill 14
E X T ENS I 0 N Sidebar: Collecting Fish and Water Samples 15
7II ]..... i...,ar.. e* Fish Health Diagnostic Facilities in Florida 16
1. II









loridians are proud of the diversity and abundance of
fish life found throughout the state, and for good
reason. More than 225 different species of fish can be
found in freshwater systems, including about 150 native
species and approximately 75 non-natives. Of course, this doesn't
even include the abundance of saltwater species!
With such a variety to choose from, it's easy to see why
Florida is considered the Fishing Capital of the World a place
where virtually every day, thousands of anglers take to the
water to land a trophy bass, catch a delicious fish dinner or enjoy
the therapeutic qualities that fishing has to offer. In fact, fresh-
water anglers contribute nearly two billion dollars to the state's
annual economy.'
However, anglers aren't the only people who care about
fish. There are just as many individuals who enjoy feeding or
watching them school under a dock. Some lake residents have
even "adopted" or named individual fish that are seen on a
regular basis. Still others feel good simply knowing that there
are fish living in their neighborhood lake, pond, or canal,
serving as indicators of the ecosystem's health.
Such strong connections to the aquatic environment may
help explain the concern that surfaces when reports of a fish kill
appear in the local media especially if large numbers of fish
are involved. Often the first assumption is that something is
terribly wrong with the lake or waterbody. Suspicions are raised
as to whether human activity, such as a chemical spill, may have
caused the fish to die. Sometimes these suspicions are war-
ranted but often they are not. What many people don't realize is
that the vast majority of fish kills in Florida are due to natural

1 According to the National Survey of Fishing, Hunting and Wildlife-Related -. "
Recreation. U.S. Census Bureau. 2001.


The Bad News
Fish kills occur frequently in Florida and most of them are natural.
It is difficult to predict when a fish kill will occur.
Even if a fish kill is predicted, there is not much that can be done
to prevent it, especially in larger waterbodies.

The Good News
In the event of a fish kill, you may see a lot of dead fish but there
are usually a lot more that are still alive.
If water quality should change for the worse, there are often many
refuges for fish to escape to.
Because fish are known to lay many eggs, their reproductive
potential is usually strong. As a result, they are generally able to
rebound from a fish kill within a couple of years.



2












N naturally occurring fish kills can be related to physical processes (e.g., rapid fluctuations in
temperature), water chemistry changes (e.g., lack of oxygen or changes in the pH), or they can be
biological in nature (e.g., stress from spawning activity, viruses, bacterial infection, parasites, etc.).
Such processes are common to every lake in Florida and generally become lethal only after a fish is
weakened by stress. As described on page 8, stress is usually caused by a number of factors in addition
to the daily challenge of living in an aquatic environment and continuously having to hide from predators.
In Florida, the vast majority of fish kills are caused by one or more natural causes. The most common
are low dissolved oxygen levels, spawning fatalities, mortality due to cold temperature, and fish parasites
or diseases. On occasion, toxic algae blooms may be suspect. The following segments provide basic
descriptions of these factors and how they can adversely affect fish health.




Fish need oxygen just as you and I do, even if they breathe a little
differently. (Fish absorb oxygen from the water as it passes over
their gills, whereas you and I use our lungs to absorb oxygen from
the air.) For optimum health, warm water fish generally require
dissolved oxygen (DO) concentrations of at least 5 parts per
million, also expressed as 5 milligrams per liter or 5 mg/L.
Just like humans, fish can endure brief periods of reduced
oxygen. However, if DO levels drop below 2 mg/L, they aren't
always able to recover.2 When concentrations fall below 1 mg/L
fish begin to die.3
The periodic depletion of dissolved oxygen in a lake or -r .:
waterbody is by far the most common cause of fish kills in Florida.
These events are easy to recognize because they usually affect
many different sizes and species of fish, whereas cold temperature-
related or spawning-related fish kills tend to affect only one or
two species. If it is a DO-related fish kill, large fish tend to be
affected first and more severely than other fish. Another clue:
small fish can be seen gulping or gasping for air at the surface just
before a fish kill occurs.
When it comes to understanding the dynamics of oxygen and
water, the most important thing to remember is that the amount of
dissolved oxygen found in an aquatic system changes constantly,
day and night. It is affected by weather, temperature, the amount
of sunlight available, and the amount of plants and animals living
in the water. Each of these factors can influence the amount of
oxygen released or removed from the water at any given time. The periodic depletion
See pages 4 -6 for more about these processes. of dissolved oxygen in
a lake or waterbody is
2 Dissolved oxygen refers to oxygen gas that is dissolved in water. by far the most common
cause of fish kills in
3 Fish kill data reported to the South Florida Water Management District documents that
87% of the fish killed in South Florida (i.e, from 1991 to 2001) occurred when surface DO Florida.
was 3 'in, L or less. Measurements were taken during or shortly after each fish kill event.

3












N naturally occurring fish kills can be related to physical processes (e.g., rapid fluctuations in
temperature), water chemistry changes (e.g., lack of oxygen or changes in the pH), or they can be
biological in nature (e.g., stress from spawning activity, viruses, bacterial infection, parasites, etc.).
Such processes are common to every lake in Florida and generally become lethal only after a fish is
weakened by stress. As described on page 8, stress is usually caused by a number of factors in addition
to the daily challenge of living in an aquatic environment and continuously having to hide from predators.
In Florida, the vast majority of fish kills are caused by one or more natural causes. The most common
are low dissolved oxygen levels, spawning fatalities, mortality due to cold temperature, and fish parasites
or diseases. On occasion, toxic algae blooms may be suspect. The following segments provide basic
descriptions of these factors and how they can adversely affect fish health.




Fish need oxygen just as you and I do, even if they breathe a little
differently. (Fish absorb oxygen from the water as it passes over
their gills, whereas you and I use our lungs to absorb oxygen from
the air.) For optimum health, warm water fish generally require
dissolved oxygen (DO) concentrations of at least 5 parts per
million, also expressed as 5 milligrams per liter or 5 mg/L.
Just like humans, fish can endure brief periods of reduced
oxygen. However, if DO levels drop below 2 mg/L, they aren't
always able to recover.2 When concentrations fall below 1 mg/L
fish begin to die.3
The periodic depletion of dissolved oxygen in a lake or -r .:
waterbody is by far the most common cause of fish kills in Florida.
These events are easy to recognize because they usually affect
many different sizes and species of fish, whereas cold temperature-
related or spawning-related fish kills tend to affect only one or
two species. If it is a DO-related fish kill, large fish tend to be
affected first and more severely than other fish. Another clue:
small fish can be seen gulping or gasping for air at the surface just
before a fish kill occurs.
When it comes to understanding the dynamics of oxygen and
water, the most important thing to remember is that the amount of
dissolved oxygen found in an aquatic system changes constantly,
day and night. It is affected by weather, temperature, the amount
of sunlight available, and the amount of plants and animals living
in the water. Each of these factors can influence the amount of
oxygen released or removed from the water at any given time. The periodic depletion
See pages 4 -6 for more about these processes. of dissolved oxygen in
a lake or waterbody is
2 Dissolved oxygen refers to oxygen gas that is dissolved in water. by far the most common
cause of fish kills in
3 Fish kill data reported to the South Florida Water Management District documents that
87% of the fish killed in South Florida (i.e, from 1991 to 2001) occurred when surface DO Florida.
was 3 'in, L or less. Measurements were taken during or shortly after each fish kill event.

3







Oxygen enters water from two main sources:

The atmosphere: The same oxygen that we breathe from the
atmosphere is also slowly and continuously being dissolved
into our oceans, lakes, rivers, streams, and ponds through a process
known as diffusion. Wind and wave action can accelerate
this process.
Photosynthesis: Photosynthesis is a process whereby algae and
aquatic plants use carbon dioxide, water, and sunlight to make
their own food. Oxygen is a by-product of this activity.
Therefore, as long as photosynthesis is taking place, oxygen is
-, continuously being released into the water.

At the same time that oxygen enters the
Aquatic environment, it is also being removed
by the following natural processes:

Biological activity in the water column refers to the regular
day-to-day functions carried on by various aquatic organisms
in a lake including algae, aquatic plants, bacteria, fish, insects,
Zooplankton, etc. Just as you and I use oxygen from the air,
these organisms are constantly using or removing oxygen from
the water. This is usually not a problem during daylight hours
because the algae and submersed aquatic plants generally
produce a surplus of oxygen via photosynthesis. However, once
the sun goes down, algae and plants are no longer able to
photosynthesize and they become oxygen consumers, instead of
oxygen producers. After a long night of limited oxygen production,
the organisms in a lake are ready for some fresh DO.
Water temperature affects how much oxygen water can hold
at a given time. As a general rule, warm water holds less oxygen
than cool water.4 In fact, not only does warmer water hold less
oxygen, it also speeds up a fish's metabolism. Of course, this
dynamic puts fish in double jeopardy; as the water becomes
warmer, fish need more oxygen for respiration," but are getting
less because warm water holds less oxygen.
Decomposing aquatic plants and/or algae can result in the
loss of oxygen in a waterbody and it works like this: once the
Just as you and I use plants or algae die, a feeding frenzy is often triggered within the
oxygen from the air, detrital aquatic community,6 as bacteria begin to break down or
"decompose" the dead vegetation. The increased activity can
aquatic organisms and result in a loss of oxygen because these organisms are working
plants are constantly harder and therefore using more oxygen. If there is a large amount
using or removing 4 There are times when cooler water may not necessarily hold more dissolved
oxygen from the water. oxygen than warm water. See Lake Turnover section described on page 5.
5 (i.e., the act of breathing)
6 (i.e., microbes and/or insects that feed on rotting vegetation and debris)

4







of dead vegetation or algae, such activity can result in a severe
loss of dissolved oxygen and, consequently, a fish kill. Lakes or
ponds with heavy populations of aquatic plants or algae are
more susceptible to this type of event and can result in large
numbers of dead fish. That is why, when using chemicals (i.e.,
algicides or herbicides) to remove algae or aquatic weeds from
a lake, it's recommended that treatments be staggered in order
to avoid large amounts of algae or plants dying all at once.7

Lake turnovers generally occur in the fall but can sometimes
occur in the summer. During hot weather, the surface water of a
lake warms much faster than deeper water. This results in a
temporary layering effect, with warm water on top and cool
water underneath. Scientists refer to this as stratification.
Because the top layer has constant access to the atmosphere, it
tends to have more oxygen than the bottom layer even though .
it's warmer.8 If a heavy wind or cold rain should occur during
these conditions, the stratification may be broken, causing the .
two layers to mix. Once this happens, oxygen-rich surface
waters are suddenly mixed with the low-oxygen bottom waters.
If the volume of low oxygen water (i.e., from the bottom of
the lake) is much greater than the oxygen-rich surface layer,
this mixing action can result in low DO levels throughout the
water column, and potentially result in a fish kill. Lakes with large amounts of

To summarize: Although oxygen depletions can happen at any aquatic plants or algae are
time, they are most likely to occur during warm summer more susceptible to oxygen-
months due to the factors described above. A combination of related problems, especially
hot weather and cloudy skies can be particularly deadly for if the plants happen to die all
fish, as the decrease in sunlight (i.e., from cloud cover) makes it
difficult for algae and plants to photosynthesize. The reduction at once.
in photosynthesis results in a decrease in oxygen being released
into the water column. When overcast skies persist for several
days, oxygen levels can become severely depleted.
Heavy thunderstorms can also have an adverse effect on
oxygen levels, especially after extended periods of dry weather
or during hot weather. If conditions have been dry for a long
time, heavy rains tend to wash large amounts of organic matter
such as dried leaves, grasses, etc. into nearby canals, lakes, and
ponds. As bacterial organisms begin to decompose the new
material, oxygen is used at a faster rate than normal. This can be
a problem during hot weather as there is less oxygen in the water.
See Figure 1 on page 6 for more on the relationship between fish kill
events and rainfall in Florida.

7 A Beginner's Guide to Water Management The ABCs (Information Circular 101).
1999. Florida LAKEWATCH. University of Florida/Department of Fisheries and
Aquatic Sciences. Page 12.
8 '. r.: cooler water has the potential to hold more oxygen, there are times when dissolved
oxygen levels are lower in cool water especially at greater depths where there is
no access to atmospheric oxygen and photosynthesis is limited due to a lack of sunlight.

5
















Th Sraph below p e s g evdec th
















13 ]:::


Rarddll L; I k
















S a m t rS i S S n 0 Sin Sot F i I












6lI










Another type of fish kill event that is both natural and common
in Florida waterbodies occurs after fish spawning activities.
This is usually due to exhaustion from courtship behavior, nest
building, and the release of eggs or milt. Fish have also been
known to suffer fatal injury from defending their young. Dur-
ing and after spawning, fish are often quite weak and any
change in the environment can stress them significantly and
lead to death.
These type of events are most common in the springtime
and early summer when the majority of the fish are spawning.'
They are generally identified by the deaths of adult fish (only),
belonging to one or two different species.




Fish kills can also be the result of a dramatic drop in air, and
consequently, water temperature. This type of event is easily
identified because it generally happens after extended periods
of cold weather and almost all of the dead fish will be cold
intolerant species. In almost every instance, these cold intolerant
species are "exotic" fish that have accidentally been introduced
to Florida waters. One example is the blue tilapia (Tilapia aurea)
from Africa's Nile River. This fish was inadvertently introduced
into Florida waterbodies in 1961 and is now successfully repro-
ducing in 18 counties. Because they are from a tropical region of
the world, blue tilapia don't fare well in cold temperatures;
they stop feeding when water temperatures drop to about 60
degrees Fahrenheit and die when it reaches approximately
45 degrees.
Those who worry about the further spread of exotic tropical
fish species can take some comfort in knowing that their
distribution is often naturally limited by their sensitivity to low
temperatures. This natural control mechanism was recently
demonstrated at Lake Alice, a small waterbody on the University
of Florida campus in Gainesville in North Central Florida. For
several years, the lake supported a population of blue tilapia
estimated to be around 12,000. However, in early January 2001,
a severe cold front passed through Gainesville bringing tempera- kills are easily identified
tures that were considerably colder than the tilapia's native kills are easily identified
African habitat. Within a week, dead tilapia began to float to because they generally occur
the surface. By the middle of the month, thousands of these fish after extended periods of
had died, while native species survived the cold snap just fine. cold weather and almost all
Several more cold fronts have effectively reduced the tilapia of the dead fish will be cold
population to almost nothing. intolerant species, such as
the blue tilapia pictured above.
9 Somefish spawn year round in Florida, but the peak season is generally from
January through April.










Another type of fish kill event that is both natural and common
in Florida waterbodies occurs after fish spawning activities.
This is usually due to exhaustion from courtship behavior, nest
building, and the release of eggs or milt. Fish have also been
known to suffer fatal injury from defending their young. Dur-
ing and after spawning, fish are often quite weak and any
change in the environment can stress them significantly and
lead to death.
These type of events are most common in the springtime
and early summer when the majority of the fish are spawning.'
They are generally identified by the deaths of adult fish (only),
belonging to one or two different species.




Fish kills can also be the result of a dramatic drop in air, and
consequently, water temperature. This type of event is easily
identified because it generally happens after extended periods
of cold weather and almost all of the dead fish will be cold
intolerant species. In almost every instance, these cold intolerant
species are "exotic" fish that have accidentally been introduced
to Florida waters. One example is the blue tilapia (Tilapia aurea)
from Africa's Nile River. This fish was inadvertently introduced
into Florida waterbodies in 1961 and is now successfully repro-
ducing in 18 counties. Because they are from a tropical region of
the world, blue tilapia don't fare well in cold temperatures;
they stop feeding when water temperatures drop to about 60
degrees Fahrenheit and die when it reaches approximately
45 degrees.
Those who worry about the further spread of exotic tropical
fish species can take some comfort in knowing that their
distribution is often naturally limited by their sensitivity to low
temperatures. This natural control mechanism was recently
demonstrated at Lake Alice, a small waterbody on the University
of Florida campus in Gainesville in North Central Florida. For
several years, the lake supported a population of blue tilapia
estimated to be around 12,000. However, in early January 2001,
a severe cold front passed through Gainesville bringing tempera- kills are easily identified
tures that were considerably colder than the tilapia's native kills are easily identified
African habitat. Within a week, dead tilapia began to float to because they generally occur
the surface. By the middle of the month, thousands of these fish after extended periods of
had died, while native species survived the cold snap just fine. cold weather and almost all
Several more cold fronts have effectively reduced the tilapia of the dead fish will be cold
population to almost nothing. intolerant species, such as
the blue tilapia pictured above.
9 Somefish spawn year round in Florida, but the peak season is generally from
January through April.


























s you've learned from reading this specific, stress triggers a series of events known
pamphlet, there are many factors that as the General Adaptation Syndrome. This
can contribute to a fish kill. However, syndrome affects a fish's metabolism and im-
stress seems to be a common element linked mune system and occurs in three phases:
with virtually every one of these events.
The term "stress" is used to describe the Phase 1 Alarm Reaction This first phase in-
physical changes that fish experience as they volves the release of certain stress hormones,
adjust to a changing environment. While it may resulting in an immediate reaction from the fish.
not be the actual cause of disease or death, it is Also known as the "flee or fight" response, the
always a predisposing factor. release of stress hormones acts as a signal to the
As with humans, there are numerous degrees fish to swim away as quickly as possible or stay
of stress and a fish can recover from many of and fight.
them, especially if it can remove itself from the
negative events it is experiencing. However, if it Phase 2 Resistance Stage The second phase
cannot escape, or the events increase in severity involves the use of a fish's energy stores to com-
or duration, the fish may be pushed beyond a pensate for the challenge it has detected (i.e., to
level from which its system can recover, flee or fight). If the stressorr" does not decline,
The typical stresses that a fish may experi- the fish will continue to use its energy reserves
ence on a daily basis, such as the predator/prey until they are depleted, leading to the third phase.
example described on page 9, are natural situations
that fish are designed to deal with. However, Phase 3 Exhaustion Phase During the
continuous stress tends to break down a fish's Exhaustion Phase there is minimal ability to
immune system and can lead to disease or death, adapt or resist death.
Examples of continual stressors include poor
nutrition, poor water chemistry, and overcrowd- Anglers are familiar with the fish behavior
ing. Multiple stresses occurring at the same time, just described as it is (hopefully) played out
can have a magnified effect and often represent many times during a fishing trip. Sometimes the
the fatal blow to a fish's health, angler wins, sometimes the fish wins. However,
the General Adaptation Syndrome is most often
The Mechanics of Stress associated with a fish's ability to survive in its
When fish experience stress, various physical normal aquatic environment full of hungry
and chemical processes occur. To be more finned predators.



8


























The following is a description of a typical The results are a prolonged reaction within
predator/prey encounter: the fish's body chemistry a contrast to the more
A largemouth bass spots a bluegill and begins to chase it. immediate "flee or fight" response described
The bluegill senses the approaching bass and attempts to earlier. Though the release of low-level hormones
escape. Stress hormones are released, triggering an increase is more gradual, it is similar in that it also
in bloodflow to the bluegill's skeletal muscles and gills, occurs in three phases:
and a decrease in bloodflow to the digestive system (a low
priority at this point). The increased bloodflow to the gills Step 1 When a fish begins to experience a
and muscle tissue allows for a burst of fast swimming, stressor, substances known as "releasors" are
If the bluegill makes it to cover before the bass produced by the hypothalamus in the brain.
swallows it, the stress stops almost immediately for the
bluegill, anyway. Once the bluegill is safe in its new Step 2 These releasors travel through the
hiding place, it can rest and slowly replenish its depleted bloodstream to the pituitary gland, where they
..;... I, i stores. However, if it is too far from cover or makes trigger the release of hormones to the kidney.
a mistake and bolts for open water, then the stressor
(i.e., the bass) will continue the chase, L. .,. up" the Step 3 The hormones themselves produce a
bluegill's...., :i. stores as it flees. Eventually the bluegill will chemical that suppresses the immune system,
exhaust its supply of quick ..,.., :r, and will begin to tire resulting in an increased susceptibility to disease.
and slow until the bass captures it with one big gulp!
In addition to these steps, there is another
This synopsis is a good example of an "all physical process that occurs that can be beneficial
This synopsis is a good example of an "all
to fish for the short term, but detrimental over
or nothing" situation where the outcome is very
the long term. When hormones are released,
distinct (i.e., recovery or death). However, there
is also a extra blood is shunted to the fish's gills, providing
is also a more complex form of the General
a quick source of oxygen and energy. However,
Adaptation Syndrome that exists when stress u
if the stress continues, the gill tissue remains
occurs at lower levels, but for prolonged periods
engorged with blood, and water flowing over
of time. When this happens, stress slowly engorged with blood, and water flowing over
the gills will remove too many salts and ions
catches up to the fish, resulting in disease and
d from the fish's bloodstream. This can be cor-
sometimes, death.
Such chronic low-level stress stimulates the rected on a short-term basis (i.e., predator/prey
Such chronic low-level stress stimulates the
chase scenario). However if the stress continues
production of a second type of hormone-induced
over a prolonged period of time, there is no
process that affects the fish's metabolism andr
smot salt balance). recovery phase and the fish will most likely
osmoregulation (water-ion salt balance).
become ill and experience a fatal outcome.


9










Fish diseases (i.e., from viruses, bacteria, and fungi) and parasites
(i.e., protozoans, crustaceans, flukes, and worms) occur naturally
in Florida lakes and under certain circumstances, fish can
contract one or more of these afflictions. Of course, a healthy
fish is usually able to fend off such problems, but if a fish is
weak from spawning or from extreme water quality conditions,
Sit has a much greater chance of getting sick or possibly dying.

SSee sidebar: Stress in Fish on pages 8 & 9.

Fish infected with parasites or diseases may have physical
clues on their bodies or they may display abnormal behavior.
Some physical clues can be obvious, such as open sores on the
body, missing scales, lack of slime, or strange growths on the
body, head, or fins. If a fish is large enough (e.g., a largemouth
Sbass), the careful observer may even notice parasites crawling
0on its skin or gills. Abnormal behavior may include swimming
weakly, lazily, erratically, or in spirals; scratching or rubbing
Fish infected with diseases or against objects in the water; twitching, darting, or convulsing;
parasites may have physical clues failure to flee when exposed to fright stimuli; gasping at the
on their bodies such as sores, or water surface or floating head, tail, or belly up.
they may display abnormal behavior. These types of fish health problems are perhaps a little
more difficult to spot in the natural environment whereas fish
farmers are all too familiar with it. In channel catfish aquaculture
ponds, for example, a protozoan known as Aurantiactinomyxon
ictaluri is known for causing the dreaded Hamburger Gill
SDisease. In some instances, it has killed up to 100% of the fish in
S an infected pond. Fish with this particular problem may exhibit
S~. 4. a reduction in feeding habits and can be seen swimming lethar-
S. gically. They may also be gasping for air at the surface and
M frequently will congregate around aeration equipment. Their
4P gills will be swollen and mottled with red and white colored
F streaks, closely resembling ground hamburger meat, hence
the name.
If a fish disease problem is suspected in a lake or pond,
it is helpful and informative if one is able to collect water
samples and also capture several live fish samples for examination
especially fish that are near death.

Note: Once dead fish are observed floating at the surface of a lake or
waterbody, decomposition is usually advanced and the fish are not
suitable for diagnostic evaluation.

For more on the correct procedures for sampling,
Fish diseases such as the dreaded see Collecting Fish and Water Samples on page 15.
"Hamburger Gill Disease" can be
devastating particularly in ponds.


10










The appearance of large amounts of algae or scum floating on
the surface of the water is often referred to as an "algae bloom". .
or "algal bloom." Such occurrences can be smelly, unsightly,
and depending on the species of algae the color of the.. .
water may even change. In some instances, a number of dead
fish may be seen floating on the surface or washed up on the *...,
shoreline. As alarming as these events may seem, there are several
factors to consider before assuming that an algal bloom is toxic:

In Florida's freshwater systems, there are relatively
few species of algae that are known to produce toxins.'"
The most common species found here are the blue-green
algae Microcystis, Cylindrospermopsis, Anabaena and
Aphanizomenon, as well as the microflagellate Prymnesiam."1
It's important to note that not all of the species within
these algal groups produce toxins; those that do, In Florida's freshwater
produce toxins in varying amounts, depending on systems, there are relatively
prevailing conditions. few species of algae that are
known to produce toxins.
While toxins produced by these algae have the potential The algae pictured below
for killing fish, there are very few cases that have been
.represent a few of the most
definitively linked to toxins. (This will most likely remain represent a few of the most
an important focus of research for years to come.) common "toxic" blue-green
algae found in Florida
Algae blooms are a natural component of nutrient-rich freshwaters.
lakes and rivers, particularly those with high levels of
nitrogen and phosphorus. Aphanizomenon.

*Algae blooms are fairly common in Florida either
because of natural geologic conditions (nutrient-rich soils) I
or human induced increases in nutrients.
Anabaena
It's thought that most algae-related fish kills are the A
result of oxygen depletion, as opposed to toxicity problems.

See the Dissolved Oxygen segment on pages 3 6
for more on this. A


Microcystis y .





10 Coastal residents are perhaps familiar with toxic-algae related fish kills that
occur periodically in coastal waters (i.e., in the form of red tides).

11 A class of single-cell organisms such as a fl.i -..ii t.i. protozoan or alga.


11













Here is no doubt that human impacts can lead to fish
kills. However, in the United States, it is also true that
point source pollution problems have been reduced
dramatically since the turn of the 20th century, or even as
recently as the 1960s, when raw sewage and industrial waste
were routinely dumped into rivers, lakes, and oceans.
(Remember the Hudson River fires?)
In recent decades such practices have been virtually
eliminated. Nowadays, if a human-induced fish kill does
occur, it's usually the result of contaminants unintentionally
being spilled or leaked into a nearby waterbody. Obviously,
the goal should be to prevent these occurrences in the first
place. But accidents happen and they can happen in any
number of ways: Highway accidents involving tanker trucks
full of fertilizers or other toxic substances have resulted in
chemicals spilling into nearby waterbodies. Barges have been
known to run into things, rupturing storage tanks and releasing
oil or other contaminants. Gas pipelines have also been
known to crack and leak oil into various aquatic environments.
In some instances, a spilled substance may not even be
toxic, but if enough of it is introduced into a system, it can be
detrimental in another way such as causing a shift in water
temperature or a change in pH.
As far as toxic spills are concerned, the effects of such an
event often depend on the toxicity of the spilled substance
and the surface area and volume of the waterbody. In other
words, if a lake is large enough, it may be able to dilute the
substance enough so that aquatic organisms, including fish,
are able to avoid any detrimental effects. Of course, this isn't
always the case.
One example of a catastrophic human-induced fish kill
involved a phosphate plant in Mulberry, Florida in December
1997. Nearly 60 million gallons of acidic process water from
the plant was accidentally dumped into Skinned Sapling
Creek, a tributary to the Alafia River. In five days, the spill
traveled 36 miles down river and changed the pH of the water
from around eight to less than four.12 A fish kill occurred along
that entire stretch of river, killing an estimated 1,300,000 fish.
Fortunately, such occurrences are rare.



S12 In addition to their sensitivity to changes in temperature and dissolved oxygen,
fish can also be detrimentally i Ft. .. -, by rapid changes in the pH of the water.

12








Sometimes, human-induced fish kills can occur from the
sheer amount of foreign substances entering a waterbody When
this happens, fish die mostly from low oxygen levels that have
resulted from an increase in biological activity in the water.

See Low Dissolved Oxygen Levels / Biological Activity
in the Water Column on pages 3 & 4. KIP -

A related example of this involved an explosion at the
Wild Turkey whiskey factory located along the banks of the
Kentucky River, near Lawrenceburg, Kentucky. The explosion
resulted in many thousands of gallons of bourbon flowing into .
the river. Officials were unsure whether it was the bourbon that
killed the fish or a lack of oxygen from the millions of aquatic
microbes that rapidly began to devour the liquor, essentially
sucking all the dissolved oxygen from the water. Hundreds of
thousands of fish died in that event.
If a human-induced spill or fish kill event should occur, _
there are often clues that will help bring attention to the problem:
E
A "film" or "slick" can sometimes be seen on the surface of the
water, or the color or clarity of the water may change."3 Strange
odors might also be noticeable or there may even be more One example of a catastrophic
obvious evidence such as large containers of the substance human-induced fish kill
sitting near the shoreline. A thorough investigation of the local involved a phosphate plant
area, along with written observations of changes in water
in Mulberry, Florida In 1997.
quality, can direct investigators to the possible contaminating
source. Observers should look for evidence of other wildlife Nearly 60 million gallons of
species being affected such as birds, frogs, snakes, turtles, etc. acidic process water from
the plant accidentally spilled

If you see an oil spill or unknown substance in a lake or waterbody, into Skinned Sapling Creek,
the best bet is to call Florida's 24-hour Hazardous Substance Hotline at a tributary to the Alafia River.
(800) 320-0519 or (850) 413-9911. In five days, the spill traveled
36 miles down river and
If a fish kill has occurred as a result of the spill or substance, changed the pH of the water
you may also want to call the Fish Kill Hotline at (800) 636-0511. from around eight to less than
four. A fish kill occurred along
that entire stretch of river,
killing an estimated 1,300,000
fish. Fortunately, such
occurrences are rare.

13 An oily sheen on the water is not always an indication of a human-induced spill.
There is a naturally occurring algae, known as Botryococcus, that produces an oily
substance that can be seen on the surface of the water. In Florida, Botryococcus
algae blooms are fairly common, especially during the summer months. Its presence
has caused some alarm among lakefront citizens, as the algal cells are red or burnt
orange in color and, in large enough concentrations, they have been known to
temporarily change the color of a lake from green to orange. Also, in some instances,
it will look very much like a gasoline spill or oil slick.


13
















f you are especially concerned or interested in finding out what caused a fish kill, you should start
Soff by collecting fish and water samples as quickly as possible. The proper procedures for collecting
are discussed on page 15. Samples must be collected within hours of the fish kill. If too much time
has already passed or if you don't have time to collect and submit samples, the following observations
can still provide important clues as to what might have happened. Once you've gathered this information,
call your local wildlife agency (listed below) to report it.

Record the date and approximate time you If possible, take a few minutes to study the
first noticed dead fish. appearance of the dead fish and record the
following observations:
Observe and record the weather Size, to the nearest inch;
conditions from the past three or four days The condition of the bodies (e.g., thin,
(e.g., temperature, amount of rainfall, cloud bloated);
cover, wind strength and direction). Are one or both eyes normal, sunken in, or
popped out ?
Record any changes in the color of the lake Are the fins clamped down, bloody, or
water (e.g., did the water change from green to frayed?
brown or black?). Are the gills discolored, bloody, or frayed?
Are there lesions or growths on the fish?
Record the type of dead fish, by species What else looks abnormal on the fish?
name, if possible.

Note: If you cannot identify a species offish, place Talk to your neighbors. Ask them if they've
one or more in a plastic bag and freeze it for identifica- noticed anything unusual about the lake in the
tion purposes only. However, DO NOT FREEZE fish past few days. Were fish gulping air at the
that you are submitting for diagnostic evaluation water's surface? Were there unfamiliar containers
(i.e.,for determining the cause of thefish kill). near the shore? Was there a "film" or "slick"
For more information on collecting and submitting present on the surface of the water? Any
fish and/or water samples for diagnostic evaluation, strange odors coming from the lake?
see page 15.
Call the Florida Fish and Wildlife
Record the number of dead fish and, if Conservation Commission (FWC) Fish Kill
possible, categorize them by species. Hotline to report the event and they will pass
it along to the appropriate regional biologist or
Note: If the dead fish are too numerous to count, enforcement officer.
try to estimate the number by first counting the
number of dead fish in a 10-foot X 10-foot area. FWC Fish Kill Hotline
Then estimate the total distance along the shoreline (800) 636-0511
and out into the water in which dead fish are present. Florida's 24-hour Hazardous
These numbers can be used to estimate the extent Substance Hotline
of the kill. (800) 320-0519 or (850) 413-9911



14










Collecting Fish and Water Samples

If you are trying to determine the cause of a fish kill, one way to improve your chances of an
accurate "diagnosis" is to obtain both fish samples and water samples from the area where the
fish kill occurred. The sooner the samples are collected, the more accurate the diagnosis will be.
Also, keep in mind that it's best to collect fish that are near death or showing signs of distress,
such as gasping for air at the surface, etc. Careful sampling techniques and packaging procedures
will also play a role in your success. The agency or fish health specialist that you report the fish
kill to may provide you with specific sampling or packaging procedures but the following
techniques may also be used. Also, be aware that there are usually fees associated with laboratory
diagnostic services. If you are unable to pay for these services, you could just try to answer the
questions on page 14 and report your observations to the nearest wildlife agency.

Note: Some commercial carriers (UPS and Fed-Ex) will ship samples, but only if they are packaged correctly.

Fish Samples Water Samples

If you are submitting fish
Live Fish samples from a fish kill
If the fish are alive and event, you should also
appear to be able to make submit a water sample.
the trip to the laboratory, When collecting a water
place them into well- sample for analysis, a few
aerated water in a heavy ply plastic bag (fish simple yet important procedures must be followed.
shipping bag or commercial freezer bag) in a Note: No matter how "clean" you think the water is,
Styrofoam cooler to regulate temperature. It's best it is important to submit a water sample for analysis.
to collect between three and five fish of each species
involved. This ensures an accurate diagnosis of the Water samle should be collected and submitted
population as a whole, in separate containers from fish samples. This is
population as a whole.
important, as the chemistry of a water sample will
Dead Fish change significantly if it contains a live or dead fish.
Use a clean (approximately) 1 quart-sized container.
Even though the usefulness of dead fish is severely
restricted for deter g the cuse of dea th, if Thoroughly rinse any foreign matter or soap residue
restricted for determining the cause of death, if
from the container before collecting your sample.
they are in good condition (i.e., eyes are clear and
the gills red), they may still be of value. Collect Submerge the empty container 6 12 inches under
between three and five fish of each species and water and hold it there until full. Place the cap back
keep them moist with wet paper towels in a heavy- on the container while it is still beneath the surface.
ply plastic bag. Pack the samples with ice in a This removes air bubbles, which can interfere with
Styrofoam cooler and then place in a shipping the dissolved oxygen measurements. Check the
carton. If the fish are obviously decomposed or sample to ensure no visible air bubbles are present.
malodorous, do not submit them.
Label sample with the following information:
Hint: If there is a very strong noxious odor associated sample location, water depth, date, time of collection.
with the dead fish, they are rarely suitable for diagnostic
evaluation. Keep water sample in cold storage once collected
(on ice or ice packs in a cooler). If shipping samples
to a lab, package them in a Styrofoam cooler and
IMPORTANT: DO NOT FREEZE SAMPLES. then inside a shipping box. DO NOT FREEZE.



15











UF/IFAS Facilities
Department of Fisheries and Aquatic Sciences
7922 NW 71st Street
Gainesville, FL 32653
Phone: (352) 392-9617 ext. 230
Email: rffloyd@ufl.edu

Zoological Medicine Service, College of Veterinary Medicine
P.O. Box 100125
Gainesville, FL 32610
Phone: (352) 392-4700 ext. 5686
Email: riggsa@mail.vetmed.ufl.edu

Florida Department of Agriculture & Consumer Services (DACS)
Note: DACS facilities require referral by a licensed veterinarian
Kissimmee Diagnostic Laboratory
2700 N. Bermuda Avenue
Kissimmee, FL 34741
Phone: (407) 846-5200

Live Oak Diagnostic Laboratory
P.O. Drawer 0
Live Oak, FL 32064
Phone: (386) 362-1216

Note: There are fees associated with any diagnostic procedure performed by state agencies or by
private consultants. T, 1.;. illi state agencies are open Monday Friday from 8:00 am to 5:00 pm.
Some private consultants may have after-hours services at an additional cost. All laboratories must
be notified prior to sample submission.

Acknowledgments , ..
Many thanks to UF/IFAS fish veterinarians, Dr. Ruth Francis-Floyd and .
Dr. Allen Riggs, for their editorial contributions and review of this material. '
Also, many thanks to Dr. Ed Phlips for his contributions on toxic algae. = :*

UNIVERSITYY OF s .
'FLORIDA _

EXTENSION



A Beginner's Guide to Water Management Fish Kills (Information Circular 107)
This document is the seventh in a series of educational publications produced
by Florida LAKEWATCH @ 2003. For more information or to obtain copies,
call 1-800-LAKEWATCH (525-3928) or (352) 392-4817.
Free copies are also available for download from our website:
http://lakewatch.ifas.ufl.edu/


16




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