UNIVERSITY OF WISCONSIN-LA CROSSE
Graduate Studies
INFECTIOUS DISEASES, PARASITES, AND DIET OF GAME FISH FROM LAKES,
RIVERS, AND STREAMS ON FORT MCCOY MILITARY INSTALLATION
A Manuscript Style Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Biology
Sarah E. Bauer
College of Science and Health Aquatic Science Concentration
December, 2010
ABSTRACT
Bauer, S. E. Infectious diseases, parasites, and diet of game fish from lakes, rivers, and streams on Fort McCoy Military Installation. MS in Biology, December 2010, 86 pp. (B. Lasee and R. Haro)
Fort McCoy biologists are concerned with emerging and invasive pathogens that could colonize fish within the waters of the military installation. An infectious disease, parasite and diet survey was conducted to document the presence of any invasive species and to establish a baseline of fish parasite communities of brook trout, brown trout, bluegill, largemouth bass, and white suckers. Fish (n = 497) were collected from 10 study sites at Fort McCoy and screened for target pathogens according to the procedures outlined in the AFS Blue Book Fish Health Section Inspection Manual. Parasite and diet data were collected on a sub-sample (n = 10-14) of each fish species from each sample site. No target viral or bacterial pathogens were detected. A total of 6,089 parasites were recovered representing 26 genera. Prevalence of infection ranged from 33% to 100% in each fish host. Two new host records were reported. Results indicated host density, water size, diet and sampling time appeared to play a role in structuring the parasite communities at Fort McCoy Military Installation.
iii ACKNOWLEDGEMENTS
I would like to thank Dr. Becky Lasee for sharing her parasitology and fish health knowledge with me. Thank you for providing me the SCEP position and training opportunities throughout my employment with the United States Fish and Wildlife
Service, La Crosse Fish Health Center. I have learned more from this experience than can be explained, and I am very grateful for the opportunity.
I would like to thank all of my committee members: Dr. Becky Lasee, Dr. Roger
Haro, Dr. Gregory Sandland, and Dr. Michael Hoffman for teaching me things they spent their careers learning and feel passionate about. Thank you for sharing your enthusiasm with me; I hope to pass the excitement and knowledge on to others. Thank you for your continued support, patience, advice, time and perspectives throughout my graduate career and the thesis writing process.
I would like to thank Dr. Gregory Sandland and Dr. Abdul Elfessi for their patience and time explaining statistical concepts to me.
I would like to thank staff at Fort McCoy Military Installation: John Noble, Steve
Rood, and Ryan Ennis for their fish collection efforts, fish transportation, patience for parasite results, and answering questions about Fort McCoy.
I would like to thank all of my co-workers at the La Crosse Fish Health Center for their continued support, fish health knowledge, advice, and entertainment. In particular, thank you Eric Leis, Corey Puzach, Ryan Katona, Lucas Purnell, Jessica Mollison, and
Beka McCann for assisting taking lengths, weights, and tissue samples from the fish.
Thanks to Corey Puzach and Jessica Mollison for processing the bacteriology samples.
Thanks to Julie Teskie and Ryan Katona for processing the trout heads.
iv I would like to thank friends and family (including my in-laws to be) for their love, encouragement, support, patience, interest and understanding throughout my graduate career.
I would like to thank Eric Leis, my best friend and future husband, for all of his assistance with fish necropsies and parasite confirmations. Thank you for your advice, guidance and continued encouragement about my success.
v TABLE OF CONTENTS
PAGE LIST OF TABLES……………………………………………………………..viii
LIST OF FIGURES………………………………………………………………x
LIST OF APPENDICES……………………………………………………….xiii
INTRODUCTION………………………………………………………………..1
Viruses………………………………………………………………...... 3
Bacteria………………………………………………….…………...... 6
Parasites………….…………………………………….……………...... 7
Diet……………………………………………………….…………...... 9
Host Species……………………………………………….……………..9
Study Objectives…...... 13
METHODS………….……………………………………………………….....14
Site Description………………………………………………………...14
Fish Collection……………………………………………………...... 17
Bacteriology.………………………………………………………...... 17
Virology...... 20
Parasitology……………………………………………………………22
Diet Analysis.……………………………………………………...... 24
Statistical Analysis……………………………………………………..24
RESULTS……………………………………………………………………..26
Bacteriology and Virology……..…………………………………….. 26
Parasitology .…………………………………………………………...26
Diet……………………………………………………………………..43
vi PAGE
DISCUSSION.………………………………………………………………….52
REFERENCES…………………………………………………………………60
APPENDICES………………………………………………………………….68
vii LIST OF TABLES TABLE PAGE
1. List of target pathogens and parasites of freshwater fish
at Fort McCoy Military Installation…………………………………...10
2. Pathogens that have been previously reported from bluegill,
largemouth bass, brook trout and brown trout ………………………...11
3. Water type and population estimates from brook trout sample
sites at Fort McCoy Military Installation ……………………………..14
4. Water type, site information, and population estimates for
bluegill and largemouth bass sample sites at Fort McCoy
Military Installation ……………………………...... 16
5. Locations, collection dates and fish species collected from 10
sampling sites from Fort McCoy Military Installation...... 18
6. Fish Species with appropriate cell lines and incubation
temperature for detection of target viruses ……………………………21
7. Prevalence, mean intensity + one standard deviation, range of
intensity of brook trout parasite taxa at Fort McCoy sampling sites…..30
8. Prevalence, mean intensity + one standard deviation, and range
of intensity of parasite taxa infecting bluegill at Fort McCoy
sampling sites ………………………………………………………….31
9. Parasite prevalence, mean intensity + one standard deviation,
and range of intensity of parasite taxa infecting largemouth bass
at Fort McCoy sampling sites ………………………………………...33
viii TABLE PAGE
10. Percentage of brown trout with each prey item in stomach
contents at each sampling site ………………...……………………...45
11. Percentage of brook trout with prey item in stomach contents
at each sampling site …………………………………………………47
12. Percentage of bluegill with each prey item in stomach contents
at each sampling site …………………………………………………49
13. Percentage of largemouth bass with each prey item in stomach
contents at each sampling site………………………………………...51
ix LIST OF FIGURES
FIGURE PAGE
1. Rivers, streams, and lakes on the Fort McCoy Military
Installation (Monroe County, Wisconsin). The black stars
represent brook trout sample locations, the white star represents
brook trout, brown trout, and white suckers sample locations,
the grey star represents brook and brown trout sample locations,
red stars represent bluegill and largemouth bass sample locations,
the green star represents bluegill sample location (Map courtesy
of Fort McCoy).……………………………………………………….15
2. Photomicrograph of Onchocleidus sp. Inset showing anchors
at higher magnification………………………………………………..28
3. Photomicrograph of Semichon’s acetic-carmine stained
Crepidostomum cooperi. Inset showing anterior end showing
oral sucker and papillae (counter-stained with fast green) at
higher magnification ………………………………………………….28
4. Photomicrograph of anterior end of Camallanus sp …………….……29
5. Photomicrograph of Spinitectus carolini.……………………………..29
x FIGURE PAGE
6. Similarity dendrogram of parasite communities infecting
largemouth bass at Fort McCoy. The horizontal gray line
represents 70% similar evaluation line. On the horizontal axis,
the first series of numbers represents the sampling site (09-157:
West Sandy Lake, 09-164: Sparta Pond, 09-179: Big Sandy Lake,
09-199: Sandy Lake), LMB refers to largemouth bass, and the
final number represents individual largemouth bass at each
sampling location……………………………………………………...35
7. Distribution of the number of parasite taxa infecting brook trout
at the Fort McCoy sampling sites ……………………………………..36
8. Parasite abundance (+ one standard error) infecting brook trout at
the Fort McCoy sampling sites. A. All parasite species; B.
Salmincola edwardsii; C. Mean length of brook trout examined for
parasites from the Fort McCoy sampling sites.……...... 37
9. Distribution of the number of parasite taxa infecting bluegill at
Fort McCoy sampling sites……………………………………………38
10. Parasite abundance (+ one standard error) infecting bluegill at
the Fort McCoy sampling sites. A. All parasite species; B.
Spinitectus carolini; C. Ancyrocephalidae; D. Posthodiplostomum
Minimum; E. Proteocephalus sp.; F. Mean length of bluegill examined
for parasites from the Fort McCoy sampling sites……………………39
xi FIGURE PAGE
11. Distribution of the number of parasite taxa infecting largemouth
bass at the Fort McCoy sampling sites bluegill from the Fort McCoy
sampling sites………………………………………………………….40
12. Parasite abundance (+ one standard error) infecting largemouth
bass at the Fort McCoy sampling sites. A. All parasite species; B.
Ancyrocephalidae; C. Proteocephalus sp.; D. Neoechinorhynchus
tenellus; E. Mean length of largemouth bass examined for parasites
from the Fort McCoy sampling sites…………………..………………41
13. Parasite abundance (+ one standard error) infecting bluegill and
largemouth bass at the Fort McCoy sampling sites. A. All parasite
species; B. Ancyrocephalidae; C. Proteocephalus sp.; D. Spinitectus
carolini …………………….………………………………………….42
14. Diet composition of four fish species from all sampling sites at Fort
McCoy.…………………………………………………………………44
xii LIST OF APPENDICES
APPENDIX PAGE
A. Flow chart for identification of bacterial pathogens from
USFWS and AFS-FHS (2007)…………...... 68
B. Recipe for preparing pepsin and trypsin digest solutions….…………..70
C. Photomicrograph of Myxobolus cerebralis spores (courtesy U.S. Fish
and Wildlife Service-B. Lasee)………………………………………...72
xiii
Introduction
Fort McCoy Military Installation (Department of Defense-U.S. Army) encompasses 60,000 acres covering two watersheds. All 60,000 acres were purchased by 1942. Little agriculture and urban development has resulted in a relatively protected environment with ample fishing opportunities (≈62,000 angling trips in 2009) (S. Rood, personal communication). While providing these angling opportunities Fort biologists try to minimize pathogen transfer and exposure by routinely conducting fish health surveys and enacting the following regulations (Fort McCoy Regulations 420-29 2009):
(1) anglers are required to have a Fort McCoy Fishing Permit and a Wisconsin Fishing
License; (2) no live bait (minnows or crayfish) can be used, with the exception that minnows can be used at two locations that have state access; (3) fish cannot be transferred between water bodies (“bucket biologist”); (4) gasoline motors are prohibited on all water bodies; (5) boats are prohibited on Sparta Pond, Alderwood, Hazel Dell,
Stillwell, and Swamp Lake; and (6) motorized vehicles (vehicles, ATVs, and snowmobiles) are prohibited on frozen lakes, ponds, rivers and streams. Any violations of the above regulations are a federal offense. Additionally, the biologists strive to make informed management decisions to minimize anthropogenic risks associated with transmitting diseases and parasites when utilizing stocking programs, transferring fish, and providing angling opportunities. It concerned Fort McCoy’s biologists that despite
1
their best efforts, invasive diseases and parasites could colonize the aquatic ecosystems at
Fort McCoy.
Invasive species can disrupt and alter ecosystem dynamics in new habitats by
competing with native species for space and food (Mack et al. 2000, Sakai et al. 2001).
In addition to competing for resources, invasive species can be carriers of diseases and
parasites to which native species may be naïve. New diseases have been arriving into
aquatic ecosystems in the Midwest due to human introductions, fish migrations, fish
transfers, and ship ballast water (Rahel 2002, Elsayed et al. 2006, Drake and Lodge
2007).
Global climate change could also have adverse effects on ecosystems. Scientists have proposed global climate change will stress and alter ecosystem dynamics worldwide resulting in reformation of ecosystem communities (Petchey et al. 1999, Mack et al.
2000, Kolar and Lodge 2002, Root et al. 2003). In aquatic ecosystems, the predicted
effects include altered thermal regimes, food web dynamics, and habitat quality and
quantity (Petchey et al. 1999, Wrona et al. 2006). In addition, global climate change
could expand the range of hosts, parasites, and infectious diseases into northern latitudes
where climatic conditions could be a life history constraint (Esch et al. 1975a, Bush et al.
2001, Root et al. 2003, Kutz et al. 2004). Furthermore, species could be lost due to
altering host range and physiology of hosts and parasites. It is predicted that areas in
higher latitudes will have more noticeable changes in climate than latitudes closer to the
equator (Root et al. 2003).
Aquatic ecosystems in the Midwest are susceptible to the spread of invasive
species into riverine environments due to the large numbers of invasive species in the
2
Great Lakes (Kolar and Lodge 2002). Invasive species can relocate between the Great
Lakes and the Mississippi River and other riverine environments through the Cal-Sag
Canal and Illinois Waterway systems. Invasive species like the round goby (Neogobius melanostomus), bighead carp (Hypophthalmichthys nobilis) and silver carp (H. molitrix) are currently utilizing this connection to expand their range.
Assessments of parasite and pathogen presence are needed to recognize if and how stressors are affecting aquatic ecosystems (Kutz 2004). We can recognize and control the spread of diseases by establishing baselines and then monitoring trends in parasites and disease outbreaks, and document invasive species. It has been suggested that parasite community alterations could be a valuable indicator for environmental changes caused by global climate change (Marcogliese 2004, Lafferty 2008). Pathogens can be used to detect abiotic and biotic stressors on populations, resulting in physiological and behavioral changes in the hosts and parasites. These responses can affect transmission of the parasites, which can result in disease outbreaks and/or changes in parasite community structure (Esch et al. 1975a, Anderson and May 1979, Bush et al.
2001, Marcogliese 2004). The impact of parasites on their hosts is often overlooked until parasites cause disease and mortalities (Marcogliese 2004).
Viruses
The viral pathogens of primary concern to Fort McCoy biologists were Viral
Hemorrhagic Septicemia Virus (VHSV), Spring Viremia of Carp Virus (SVCV) and
Largemouth Bass Virus (LMBV). These viruses have been detected in Wisconsin and have been associated with multiple fish kills. They are viruses of primary concern due to
3
their presence in Wisconsin waters, their pathogenicity, and regulatory concern by state, federal and international agencies.
Viral hemorrhagic septicemia virus (VHSV) is a Novirhabdovirus in the family
Rhabdoviridae that was originally reported to cause high rates of mortalities in rainbow trout (Oncorhyncus mykiss) and other salmonids in Europe (Elsayed et al. 2006,
Bergmann and Fichtner 2008). In the U.S., two genotypes of the virus have been described, IVa in the Pacific Northwest and IVb in the Great Lakes (Elsayed et al. 2006,
Groocock et al. 2007). In the Pacific Northwest, VHSV IVa is associated with limited disease in pacific herring (Clupea harengus pallasi), pacific cod (Gadus macrocephalus) and pacific salmon (Onchorhynchus tshawytscha) (Meyers and Winton 1995).
VHSV IVb may be a recent introduction into the Great Lakes because the virus was not previously detected (Elsayed et al. 2006). In 2003, VHSV IVb was isolated from muskellunge (Esox masquinongy) from Lake St. Clair (Michigan, USA) and in 2005, the virus was responsible for a fish kill of freshwater drum (Aplodinotus grunniens) in Lake
Ontario (Elsayed et al. 2006, Groocock et al. 2007). In 2006, VHSV was associated with large-scale kills of multiple fish species from lakes St. Clair, Erie, and Ontario (Elsayed et al. 2006, Groocock et al. 2007). The virus has been isolated from moribund fish and in subclinical fish that otherwise appeared to be healthy (Elsayed et al. 2006, Lumsden et al.
2007). In 2008, the virus was isolated from Clear Fork Reservoir (Ohio, USA) in muskellunge, bluegill (Lepomis machrochirus) and largemouth bass (Micropterus salmoides) that appeared healthy. This was the first report of the virus outside of the
Great Lakes drainage (E. Leis, La Crosse Fish Health Center, USFWS and D. Insley,
Ohio Department of Natural Resources, personal communications).
4
Infected fish shed VHSV IVb through urine and ovarian fluids and the virus enters a naïve host via the gill epithelium (Lumsden et al. 2007). Also, it has been detected in the parasitic leech Myzobdella lugubris making it a potential vector of the virus (Faisal and Schulz 2009). VHSV has the ability to infect a wide array of fish species from a multitude of different families and does not appear to discriminate between ages classes (Gagne 2007, Faisal and Faisal 2010). This broad host range makes
VHSV IVb a major threat to aquatic ecosystems (Elsayed et al. 2006). Currently, VHSV
IVb is considered one of the most significant pathogens in fish health history and is a reportable disease by state, federal and international agencies.
Another recent invasive virus in North America is spring viremia of carp virus
(SVCV). SVCV is a Vesiculovirus in the family Rhabdoviridae that primarily infects carp and other cyprinid species and occurs primarily in Europe (Fijan 1999, Goodwin
2002, Miller 2003, Dikkeboom et al. 2004, Dixon 2008). It first appeared in North
America in 2002, with two concurrent outbreaks in common carp (Cyprinus carpio), one at a goldfish and koi farm in North Carolina and the other in a wild population of common carp in Cedar Lake, Wisconsin. It is estimated that 20,000 carp died in Cedar
Lake (Dikkeboom et al. 2004). It has been experimentally demonstrated that northern pike (E. lucius) and rainbow trout can be infected with SVCV (Dixon 2008). In the wild, the virus has been detected from apparently healthy bluegill and largemouth bass from a lake in Ohio (B. Lasee, U.S. Fish and Wildlife Service, personal communication). SVCV is transmitted horizontally through feces, urine and gill mucus. It has been shown that the parasitic louse, Argulus foliaceus, and the fish leech, Piscicola geometra, can be vectors of SVCV (Miller 2003). The virus generally results in disease outbreaks at water
5
temperatures between 15-20°C (Goodwin 2002). SVCV is also a reportable disease by
state, federal and international agencies.
Largemouth bass virus is a Ranavirus in the family Iridoviridae (Mao et al. 1999).
The origin of the largemouth bass virus is unknown, but it is genetically similar to two
Asian fish viruses: the doctor fish virus (DFV) and the guppy virus 6 (GV6) (Mao et al.
1999). LMBV may be an introduced virus via the aquarium trade or it could have been previously undetected due to limited sampling (Mao et al. 1999). LMBV was first isolated in 1991 from largemouth bass in Florida, and in 1995, LMBV was associated with a bass kill in South Carolina (Grizzle and Brunner 2003). The virus has been isolated from numerous Midwest localities (USFWS-Wild Fish Health Survey Database).
LMBV has only been associated with fish kills of adult largemouth bass. Disease outbreaks are stress related events and often occur during the summer when water temperatures are high (Grant et al. 2003, Grizzle and Brunner 2003). Bluegill, smallmouth bass (M. dolomieu), striped bass (Morone saxatilis), rock bass (Ambloplites rupestris) chain pickerel (E. niger) and freshwater drum (A. grunniens) can be carriers
(carry the virus but do not exhibit signs of disease) of the virus (Grant et al. 2003, Grizzle and Brunner 2003).
Bacteria
Many bacterial species occur naturally in the aquatic environment, some of which are opportunistic pathogens of fish (Rottmann et al. 1992, Cipriano 2001). Bacterial pathogens of concern are Aeromonas salmonicida (etiologic agent of Furunculosis),
Yersinia ruckeri (Enteric Redmouth), Edwardsiella ictaluri (Enteric Septicemia), and
Aeromonas hydrophila and other Aeromonas spp. (Motile Aeromonas Septicemia). All
6
have been associated with disease outbreaks in fish in cultured and\or wild populations
(Post 1987, Lasee 1995, Bergh 2008). Generally, fish are not prone to bacterial
infections because their mucus, scales and skin function as physical barriers against
bacterial invasion (Rottmann et al. 1992). Environmental stressors such as spawning,
overcrowding, physical injuries, and poor water quality are known to be factors
influencing bacterial disease outbreaks in fish (Hazen et al. 1981, Rottmann et al. 1992,
Cipriano 2001).
Parasites
Natural parasite infections can result in mortalities or reduction in fitness of their hosts if the infection is severe or if the host is stressed. Mortalities of juvenile brook trout (Salvelinus fontinalis) were associated with infestations of larval diphyllobothriids migrating through the viscera and heart (Hoffman and Dunbar 1961). Infections of larval Proteocephalus ambloplitis have been suggested to reduce fertility in smallmouth bass (Micropterus dolomieu) (Esch and Huffines 1973). Additionally, mortalities of bluegill (L. machrochirus) in the Mississippi River have been correlated with infections from Allacanthochasmus sp. (Marcogliese 2004).
Invasive parasites can have disastrous effects on native fish in North America.
The Asian tapeworm (Bothriocephalus acheilognathi) is thought to have been inadvertently introduced into the United States via importation of grass carp
(Ctenopharyngodon idella). Asian tapeworms can cause blockages of the intestine and mucosal discharge that can result in anemia and death in fish (Kolar et al. 2005). In the southwest, the parasite has had devastating effects on native cyprinid fish species (Bean
2008). Currently, Asian tapeworm is expanding its range and hosts throughout North
7
America and now has been found in the Great Lakes, Detroit River, Cal-Sag Canal, and
Lake Winnipeg (Manitoba, Canada) (Hoffman 1999, Choudhury et al. 2006, Marcogliese
2008, USFWS-Wild Fish Health Survey Database). Asian tapeworm has been detected in the Midwest in fathead minnow (Pimephales promelas), bluntnose minnow (P.
notatus), common carp, white bass, walleye (Zander vitreum), sauger (Z. canadense),
northern pike, and goldeye (Hiodon alosoides). There are reproducing populations of
Asian Tapeworm in Wisconsin (Choudhury et al. 2006).
Myxobolus cerebralis is an invasive myxosporean parasite that infects the
cartilage of salmonid fish resulting in Whirling Disease (Hoffman 1990, Lasee 1995,
Bergersen and Anderson 1997). The parasite can infect wild and hatchery reared
salmonids (Lasee 1995). Signs of infections include black tail, skeletal deformities, and
“whirling” behavior (Hoffman 1999, Steinbach-Elwell et al. 2009). Infections can lead to the decline or elimination of fish year classes in wild populations (Bergersen and
Anderson 1997). Mortalities associated with M. cerebralis infections can be a result of the fish’s inability to eat, avoid predators, or from direct physical damage associated with the parasite (Steinbach-Elwell et al. 2009).
Myxobolus cerebralis evolved as a non-pathogenic parasite of brown trout (Salmo trutta) in Europe and Asia (Hoffman 1990, Bergersen and Anderson 1997). The suggested route of introduction into North America was the transfer of infected fish or
fish products worldwide (Hoffman 1990, Bergersen and Anderson 1997). It was first detected in 1956 in Pennsylvania and has since spread throughout the United States
(Hoffman 1990, Bergersen and Anderson 1997). Currently, it has been detected in at
8
least 21 states in wild populations including Michigan (Bergersen and Anderson 1997).
It has not been found in Wisconsin waters (USFWS-Wild Fish Health Survey Database).
Diet
Parasites with complex life cycles tend to move from host to host via trophic interactions. This makes parasites roles in food webs critical and provides insight about trophic interactions (Marcogliese and Cone 1997). For example, variation in the diets between largemouth bass and bluegill from the lower Mississippi River influenced the infection rates of Proteocephalus ambloplitits. Bluegill ingested more copepods
(intermediate host of P. ambloplitis) than largemouth bass, which corresponded to bluegill having a higher prevalence of P. ambloplitis than largemouth bass (Fischer and
Kelso 1990).
Host species
Examining cool and warmwater fish species at Fort McCoy for changes in historical disease patterns and parasite presence could be a means of evaluating if global climate change is altering aquatic ecosystems, as well as, monitoring the spread of disease and invasive species. Bluegill, largemouth bass, brook trout, brown trout, and white suckers (Catastomus commersoni) have been reported to be carriers of major taxa of parasites including: Fungi, Monogenea, Trematoda, Cestoidea, Nematoda,
Acanthocephala, Hirudinea, Mollusca, and Crustacea (Hoffman 1999). Also, these fish are carriers of some of the target bacterial and viral pathogens for this study (Tables 1-2).
9
Table 1. List of target pathogens and parasites of freshwater fish at Fort McCoy Military Installation.
Pathogen Classification
Aeromonas salmonicida a Bacterial
Yersinia ruckeri a Bacterial
Edwardsiella ictaluri a Bacterial
Aeromonas hydrophila Bacterial
Infectious Hematopoietic Necrosis Virus a, b Viral
Infectious Pancreatic Necrosis Virus a Viral
Oncorhynchus Masous Virus a Viral
Largemouth Bass Virus a Viral
Bluegill Virus Viral
Spring Viremia of Carp Virus a ,b, c Viral
Viral Hemorrhagic Septicemia Virus a, b, c Viral
Myxobolus cerebralis a, c Parasitic
Bothriocephalus acheilognathi a, c Parasitic a United States Fish and Wildlife Service certifiable pathogen. b Office International des Epizooties (OIE) certifiable pathogen. c Invasive
Bluegill-Bluegill are widely distributed in warmwater and have a diet including
small insects, crayfish, fish, amphipods, worms, and vegetation (Pfleiger 1975, Eddy and
Underhill 1976, Becker 1983). Bluegill are gregarious and their schooling behavior can
help spread disease via horizontal transmission. Historically, bluegill have been hosts
for many parasites and some of the target pathogens (Table 2). They are important prey
for other fish and birds, making them a potential intermediate host and disease vector.
10
Table 2. Pathogens that have been previously reported from bluegill, largemouth bass, brook trout and brown trout.
Fish Species Target Pathogen
Bluegill Largemouth Bass Virus Spring Viremia of Carp Virus Viral Hemorrhagic Septicemia Bluegill Virus
Largemouth Bass Aeromonas hydrophila Largemouth Bass Virus Spring Viremia of Carp Virus Viral Hemorrhagic Septicemia Bluegill Virus
Brook Trout Aeromonas salmonicida Yersinia ruckeri Infectious Pancreatic Necrosis Virus Myxobolus cerebralis
Brown Trout Aeromonas salmonicida Yersinia ruckeri Infectious Pancreatic Necrosis Virus Viral Hemorrhagic Septicemia Myxobolus cerebralis
Largemouth bass-Largemouth bass are a warmwater carnivorous fish, whose diet
is variable, ranging from water fleas and small crustaceans to fish, large insects and frogs,
depending on the age and size of the fish (Pfleiger 1975, Eddy and Underhill 1976,
Becker 1983). Largemouth bass exhibit schooling behavior when they are fry and
immature fish. Occasionally, adults will school to hunt (Becker 1983). Similar to the bluegill, this behavior in bass can aid in the transmission of diseases and parasites.
Wisconsin appears to be the northern limit of the distribution of largemouth bass (Becker
1983).
11
Brook trout-Brook trout are coldwater fish, and the only native trout in inland
Wisconsin waters (Eddy and Underhill 1976, Becker 1983). Brook trout can be found in cool, clear streams where the annual maximum water temperature is less than 20°C
(Becker 1983). The diet of brook trout is usually made up of insects and insect larvae, and occasionally amphipods, seeds, fish, and crustaceans (Eddy and Underhill 1976,
Becker 1983). Marginal habitats for brook trout can be invaded by warmwater species like brown trout, northern pike, yellow perch (Perca flavescens), largemouth bass, and bluegill (Becker 1983), potentially exposing brook trout to new pathogens, parasites and increase inter-specific competition.
Brown trout-Brown trout were introduced into North America from Central
Europe. They were first introduced into Wisconsin in 1887, when eggs were shipped to the Bayfield Fish Hatchery. The trout were reared and then stocked into Wisconsin waters (Becker 1983). Brown trout are a coldwater species that have been established in most waterways and their habitat requirements are less strict than that of brook trout
(Eddy and Underhill 1976, Becker 1983). The upper lethal temperature limit for brown trout is 25.6°C (Becker 1983). They are opportunistic feeders, consuming leeches, snails, crayfish, freshwater shrimp, fish, insects, and insect larvae (Pfleiger 1975, Eddy and
Underhill 1976, Becker1983).
White suckers-White suckers reside in environments ranging from small creeks to large lakes and are tolerant of a wide range of environmental conditions like pollution and turbidity (Pfleiger 1975, Eddy and Underhill 1976, Becker 1983). They are suction feeders consuming anything on the bottom, typically protozoans, diatoms, small crustaceans, immature aquatic insects, and bloodworms (Pfleiger 1975, Becker 1983).
12
White suckers tend to school and are an important forage fish for piscivorous fish and
birds (Becker 1983), which can aid in the transmission of disease.
Study Objectives
Largemouth Bass Virus (LMBV), Bluegill Virus (BGV), Viral Hemorrhagic
Septicemia Virus (VHSV) and Yersinia ruckeri have been detected in Wisconsin. Also,
Infectious Pancreatic Necrosis Virus (IPNV) and Myxobolus cerebralis have been
detected in the Upper Peninsula of Michigan (National Wild Fish Health Survey
Database). The most significant threats to the Fort McCoy fisheries are VHSV and M.
cerebralis. VHSV has caused large scale mortalities in sport fish in the Great Lakes and
brook trout are highly susceptible to M. cerebralis. Other viral pathogens like
Largemouth Bass Virus (LMBV) and Bluegill Virus (BGV) could also be detrimental to
the Fort McCoy fisheries because of their pathogenicity and host specificity to
largemouth bass and bluegill, respectively. In this study, 10 study sites at Fort McCoy
Military Installation were surveyed for pathogens and parasites of white sucker, brook
trout, brown trout, bluegill and largemouth bass. The target pathogens were selected due
to the severity of disease they cause and their regulatory concern to state, federal and
international agencies (Table 1). The parasites and diet of each fish species were
cataloged and the absence of any invasive parasites was documented. For each parasite
species, prevalence, mean intensity, abundance, and range of intensity were calculated.
Parasite communities were described for each water body and within each host species.
Parasite communities were compared among host species and water body.
13
Methods
Site Description
Three streams (Silver, Tarr, and Sparta Creeks), one river (South Fork La Crosse
River) and one stream impoundment (East Silver Lake) were sampled for brook trout
(Fig. 1). The population estimates of the brook trout per mile were different between sampling sites (Table 3). Three man made lakes (West Sandy, Sandy, and Big Sandy
Lakes) and one stream impoundment (Sparta Pond) were sampled for bluegill and largemouth bass (Fig. 1). One additional stream impoundment (Stillwell Lake) was sampled for bluegill (Fig. 1). Each body of water had different surface area, maximum depth, and average depth (Table 4). The population estimates of the bluegill and largemouth bass per acre were different between sampling sites (Table 4).
Table 3. Water type and population estimates from brook trout sample sites at Fort McCoy Military Installation.
Location Type No. of Trout per Mile
Silver Creek Stream 568a
Tarr Creek Stream 1197a
Sparta Creek Stream 1093
South Fork La Crosse River River 554
East Silver Lake Impoundment 282b
a Population estimate includes brown trout per mile. b Population estimate is number of brook trout per acre. *Data courtesy of Fort McCoy Military Installation
14
Figure 1. Rivers, streams, and lakes on the Fort McCoy Military Installation (Monroe County, Wisconsin). The black stars represent brook trout sample locations, the white star represents brook trout, brown trout, and white suckers sample locations, the grey star represents brook and brown trout sample locations, red stars represent bluegill and largemouth bass sample locations, the green star represents bluegill sample location (Map courtesy of Fort McCoy).
15
Table 4. Water type, site information, and population estimates for bluegill and largemouth bass sample sites at Fort McCoy Military Installation.
Location Type Surface Area (acres) Depth (m) No. of Fish per Acre . Average Maximum Bluegill Largemouth bass
West Sandy Lake Lake 9 3.6 5.5 279 62
Sparta Pond Impoundment 4 1.5 3.4 616 182
Big Sandy Lake Lake 19 4.6 6.4 192 113
Sandy Lake Lake 12 3.6 5.5 206 56
Stillwell Lake Impoundment 5 1.8 3.6 597 N/A1
1Not applicable *Data courtesy of Fort McCoy Military Installation.
16
Fish Collection
Brook trout were electro-shocked from four locations in October 2008 and one
location in June 2009 (Fig. 1, Table 5). White suckers and brown trout were collected at
some locations with the brook trout (Fig. 1, Table 5). Bluegill and largemouth bass were
electro-shocked and fyke netted from four locations between May and July 2009. In
September 2009, bluegill were collected from one other location (Fig. 1, Table 5). The
fish were transported in holding tanks from Fort McCoy to the La Crosse Fish Health
Center (United States Fish and Wildlife Service, Onalaska, WI). Upon arrival, the fish
were euthanized with an overdose of tricane methanesulfonate (MS-222). They were
then sorted by species and individually weighed and measured. A longitudinal mid-
ventral abdominal incision was made near the pectoral fin and extended to the base of the
anal fin for each fish prior to sampling for bacteria, viruses and parasites. Gender for
each fish was recorded.
Bacteriology
Up to 30 individuals (minimum 25) of each fish species per site were screened for
bacterial pathogens. The posterior kidney of each fish was stabbed with a 1 µL sterile
loop and streaked onto a brain heart infusion agar (BHIA) slant. The slants were
incubated for a minimum of five days at 20°C. A BHIA plate was streaked for isolation of individual colonies from the mixed bacterial growth in slants. Each bacterial isolate was identified according the procedures outlined in AFS Blue Book Fish Health Section
(USFWS and AFS-FHS 2007) and using the flow chart for presumptive identification
(Appendix A). In addition, all creamy white to tan colonies were screened for
Aeromonas hydrophila with the following positive characteristics: cytochrome oxidase,
17
Table 5. Locations, collection dates and fish species collected from 10 sampling sites from Fort McCoy Military Installation.
Location Date Collected No. of Fish Examined _ Mean Length (mm) Mean Weight (g)
Fish species Target Pathogens Parasites
Silver Creek October 2008
Brook trout 30 10 200.2 89.4
Brown trout 29 14 297.5 266.8
White suckers 26 10 236.9 210.2
Tarr Creek October 2008
Brook trout 30 10 142.7 50.4
Brown trout 30 10 215.0 129.8
Sparta Creek October 2008
Brook trout 30 10 162.7 58.1
South Fork La Crosse River October 2008
Brook trout 30 10 147.9 41.5
West Sandy Lake May 2009
Bluegill 28 12 151.9 89.0
Largemouth bass 30 12 265.8 272.7
18
Table 5. Continued.
Location Date Collected No. of Fish Examined _ Mean Length (mm) Mean Weight (g)
Fish species Target Pathogens Parasites
Sparta Pond May 2009
Bluegill 29 10 143.2 75.1
Largemouth bass 30 14 212.7 173.9
Big Sandy Lake June 2009
Bluegill 30 10 167.9 112.6
Largemouth bass 30 10 277.9 240.5
East Silver Lake June 2009
Brook trout 30 10 185.3 80.0
Sandy Lake July 2009
Bluegill 25 10 140.3 79.7
Largemouth bass 30 11 254.1 194.0
Stillwell Lake September 2009
Bluegill 30 10 115.2 39.6
19
motility, OF glucose, gelatinase, indole, esculin, arabinose, maltrose, and yellow growth
on selective Rimler-Shotts plates.
Virology
Up to 30 individuals (minimum 25) of each fish species per site were screened for
viral pathogens. Tissue samples from up to five fish were pooled into a single sample. A sample (0.2 g total tissue) of the posterior kidney and spleen were removed from each fish and diluted 1:10 in Hanks Balanced Salt Solution (HBSS). For the centrarchids, a sample of the swim bladder was also collected for detection of largemouth bass virus
(LMBV). The tissue was homogenized in HBSS using a stomacher (Stomacher 80
Biomaster-Seward) and centrifuged at 2800 rpm at 4°C for 15 min. Then 1 ml of supernatant was diluted into 1 ml of HBSS. Diluted samples were then incubated at 4°C
for 12-24 h or at 15°C for 2 h. The original tissue samples were stored at 4°C until completion of testing. After the incubation, the diluted samples were centrifuged (2800 rpm at 4°C for 15 min) and plated (0.1 ml per well) in duplicate on the appropriate cells lines in 24 well plates (Table 6). Each plate accommodated 12 pooled samples. The plates were then rocked on a plate rocker at room temperature for 45 to 60 minutes. Then
0.5 ml of Eagle Minimum Essential Medium (MEM) supplemented with 1.1% penicillin/streptomycin, 0.27% Nystatin, 0.11% gentamicin, 1.1% l-glutamine, and 10% fetal bovine serum was added to each well, and the plate was sealed with a pressure sensitive film, and incubated at the appropriate temperature (Table 6) (Puzach 2006).
Plates were monitored for cytopathic effect (CPE) twice weekly for 21 days.
Wells exhibiting CPE were passed onto fresh cells as follows. Duplicate wells exhibiting
CPE were combined, filtered using a 0.8/0.2 µL double membrane filter, diluted 1:5 (1
20
Table 6. Fish Species with appropriate cell lines and incubation temperature for detection of target viruses.
Fish Species Susceptible Viruses* Cell Lines** Incubation Temperatures
Bluegill IPNV CHSE 15°C LMBV BF-2 25°C SVCV EPC/BF-2 15°C/25°C VHSV EPC 15°C BGV BF-2 25°C
Brook trout IHNV EPC/CHSE 15°C IPNV CHSE 15°C OMV CHSE 15°C VHSV EPC 15°C
Brown trout IHNV EPC/CHSE 15°C IPNV CHSE 15°C OMV CHSE 15°C VHSV EPC 15°C
Largemouth bass IPNV CHSE 15°C LMBV BF-2 25°C SVCV EPC/BF-2 15°C/25°C VHSV EPC 15°C
White sucker IPNV CHSE 15°C VHSV EPC 15°C FHM 25°C
* Viruses: IHNV-Infectious Hematopoietic Necrosis Virus; IPNV-Infectious Pancreatic Necrosis Virus; LMBV- Largemouth Bass Virus; OMV-Onchorhynchus masou Virus; SVCV-Spring Viremia of Carp Virus; VHSV-Viral Hemorrhagic Septicemia Virus; BGV-Bluegill Virus. ** Cell Lines: CHSE-Chinook Salmon Embryo; BF-2-Bluegill Fry; EPC-Epithelioma Papulosum Cyprini; FHM-Fathead Minnow.
ml sample to 5 ml HBSS) and plated onto 24 to 48 h old cells (original cell line). The resets were then monitored for CPE for an additional 14 days. Wells not exhibiting CPE prior to days 10 to 14 were blind passed. Blind passage consisted of re-inoculating one
21
unaffected well from all samples not exhibiting CPE. Up to 5 samples were pooled
together and plated as previously described. Cells were monitored for CPE for 14 days.
Parasitology
Ten to fourteen individuals of each fish species from each site were screened for external and internal parasites. After bacteriology and virology sampling, the fish were examined fresh for parasites (<48 h) or flash frozen, using ethanol cooled to -80°C.
Super cooled ethanol was poured over whole fish and frozen fish were stored in a freezer
(-20°C) until the necropsy was completed.
Frozen fish were thawed prior to parasite necropsy. First, the fish were examined for external parasites by visually inspecting the fins and scales. The eyes and gills were removed from each fish and examined using a stereomicroscope. After external examination, the internal organs were removed and placed into a Petri dish containing filtered water. The body cavity was visually inspected for parasites. The swim bladder and gastro-intestinal tract were cut open with a longitudinal incision, flushed with filtered water and examined for parasites with aid of a stereomicroscope. The gonads and liver were teased apart in filtered water and examined for parasites using a stereomicroscope.
All parasites found were recorded for site location, quantity, and stored for identification. Nematodes and copepods were fixed and stored in glycerine-alcohol
(Dailey 1996). All other parasites were fixed and stored in alcohol-formol-acetic acid
(AFA) fixative until they could be stained and mounted for identification (Dailey 1996).
Identification of parasites was done using the keys of Moravec and Arai (1971), Williams
(1977), Baker (1979), Jilek and Crites (1982a), Beverley-Burton (1984), Amin (1985),
Caira (1985), Scholz (1997), and Hoffman (1999).
22
In addition to the parasitology procedures described above, salmonids were screened for the parasite Myxobolus cerebralis. Screening for M. cerebralis was done following the Pepsin-Trypsin Digest (PTD) method outlined in the NWFHS Laboratory
Procedures Manual (Puzach 2006). Heads or dermal biopsy punches were taken from the fish prior to quick freezing for parasite necropsy. Heads or biopsy punches were pooled into groups of 5 and stored at -20°C. The screening process for M. cerebralis was as follows:
1. Heads or punches were thawed in a refrigerator overnight.
2. Heads were soaked in 60°C water bath for up to 60 minutes.
3. A 850 µm sieve was used to remove soft tissue from bones and cartilage by
scraping the flesh across sieve while flushing with water. (Soft tissue was
disinfected in a 10% chlorine solution prior to discarding).
4. Bones and cartilage were placed in a disposable weigh boat and left at room
temperature overnight to dry.
5. Bone and cartilage (heads) weighed.
6. 0.5% pepsin at a ratio of 20 ml pepsin solution per gram of heads was added to
the bones and cartilage (Appendix B).
7. The mixture was placed into a blender and mixed on the highest setting for 2 to 3
minutes.
8. The mixture was transferred to a flask and placed into a shaker bath and agitated
for at least one day at 37°C.
9. The solution was poured into 50 ml centrifuge tube(s).
10. Tubes were centrifuged at 1500 x g for 10 minutes.
23
11. A wet mount of the solution was made and screened for spores using a compound
microscope at 200x or 400x total magnification. 100 fields were examined for
spores (Appendix C). Finding ovoid spores with equal polar capsules with an
approximate length of 8.7 µm and width of 8.2 µm (Appendix C) would have
been considered a presumptive positive (Lom and Hoffman 2003).
12. The supernatant was discarded into 10% chlorine solution.
13. 0.5% trypsin at a ratio of 20 ml trypsin solution per gram of heads was added to
the bones and cartilage and put into a beaker (Appendix B).
14. The pH was adjusted to 8.5 with 1 N NaOH.
15. The beaker was agitated in a 25°C shaker bath for at least 30 minutes.
16. The digested trypsin mixture was poured through a cheesecloth into the 50 ml
centrifuge tube used in step 9. The cheesecloth was autoclaved after use.
17. The tubes were centrifuged at 1500 x g for 10 minutes.
18. A wet mount was prepared and examined for spores as described in Step 11.
Diet Analysis
The contents of the stomach were flushed into a watch glass using filtered water according to the procedures outlined by Bowen (1996). Food items were identified to family using keys of Hilsenhoff (1981) or Pennak (1978). Unknown specimens were stored in 95% ethanol for later identification.
Statistical Analysis
Prevalence (number of infected fish / number examined x 100), mean intensity
(average number of parasites/number of infected fish), abundance (average number of parasites / all hosts examined), and range of intensity (minimum and maximum number
24
of parasites observed) was calculated for each parasite species infecting each fish species
at each body of water according to Margolis et al. (1982).
SPSS statistical software (17.0) and Primer-E software (Primer 6) were used for
statistical analysis of the data. One-way and Two-way ANOVA with Scheffe’s post hoc
test was used to compare parasite intensities between water bodies and fish species, with
P = 0.05 as the level of significance. Using Primer-E software (Primer 6) the data was square root transformed and then a Bray-Curtis similarity matrix was constructed. Using the similarity matrix Primer-E constructed a similarity dendrogram of the parasite communities for each host species.
25
Results
Bacteriology and Virology
Between October 2008 and September 2009, 497 fish were collected and examined for target pathogens from 10 bodies of water at Fort McCoy. No target bacterial or viral pathogens were detected in any of the tissue samples. No novel viruses were detected from any fish species.
Parasitology
In total, 6,089 parasites representing 26 genera were recovered from 183 fish examined for parasites. Parasites were recovered from gills, fins, eyes, gastro-intestinal tract, liver, gonad tissue, and viscera of the fish. None of the parasites were identified as invasive species. Parasite representatives of Monogenea from the family
Ancyrocephalidae (Actinocleidus sp., Haplocleidus sp., Onchocleidus sp. (Fig. 2),
Syncleithrum sp. and Tetracleidus sp.), Digenea (Clinostomum complanatum,
Crepidostomum cooperi (Fig. 3), C. fausti, Diplostomulum scheuringi, Lissorchis sp.,
Neascus sp., Posthodiplostomum minimum and Proterometra sp.), Cestoidea
(Biacetabulum biloculoides, Bothriocephalus cuspidatus, larval Bothriocephalus sp., larval and adult Eubothrium sp., Glaridacris catostomi, larval and adult Proteocephalus sp.), Acanthocephala (Neoechinorhynchus tenellus), Nematoda (Camallanus oxycephalus, larval Camallanus sp. (Fig. 4 ), larval Contracaecum sp., Cystidicoloides sp., Rhabdochona cascadilla, and Spinitectus carolini (Fig. 5)), Hirudinea (Myzobdella
26
lugubris), and Crustacea (Achtheres pimelodi and Salmincola edwardsii) were recovered
from the ten study sites on Fort McCoy. Thirty-three percent of the brown trout, 50% of
the white suckers, 82% of the brook trout, and 100% of both bluegill and largemouth bass
were infected with at least one parasite. Parasite prevalence and mean intensities varied by water body (Tables 7-9).
The parasite communities of brook trout (data not shown), bluegill (data not
shown), and largemouth bass were analyzed using Bray-Curtis Similarity matrixes.
Individual fish were linked based on the similarity between their parasite communities
(Fig. 6). Using a similarity greater than 70%, parasite communities of each host species
were examined for relationships between sample site and host’s gender and size. No
relationship existed with regards to sample site, gender and size of the fish.
White suckers- The digenetic trematode, Lissorchis sp., and at least two
caryophyllaeid species, Biacetabulum biloculoides and Glaridacris catostomi, were
recovered from the white suckers from Silver Creek (Table 5, Fig. 1). Two other
caryophyllaeid specimens were recovered, but could not be identified because of poor fixation. Lissorchis sp. had a prevalence of 30%, with a mean intensity of 2.0 and range
of intensity of 1-3. The caryophyllaeids infected 30% of the white suckers with a mean
intensity of 1.3 and range of intensity of 1-2.
Brown trout- No parasites were recovered from the brown trout sampled from
Silver Creek. One species, Rhabdochona cascadilla, was recovered from brown trout
sampled from Tarr Creek (Table 5, Fig. 1). R. cascadilla had a prevalence of 70%, with a
mean intensity of 5.3 and a range of intensity of 1-15.
27
Figure 2. Photomicrograph of Onchocleidus sp. Inset showing anchors at higher magnification.
Figure 3. Photomicrograph of Semichon’s acetic-carmine stained Crepidostomum cooperi. Inset showing anterior end showing oral sucker and papillae (counter-stained with fast green) at higher magnification.
28
Figure 4. Photomicrograph of anterior end of Camallanus sp.
Figure 5. Photomicrograph of Spinitectus carolini.
29
Table 7. Prevalence, mean intensity + one standard deviation, range of intensity of brook trout parasite taxa at Fort McCoy sampling sites.
Parasite Silver Creek Tarr Creek Sparta Creek S. Fork La Crosse River E. Silver Lake
Digenea
Crepidostomum fausti - - - 20,1 + 0.0(1-1) 10,1+ undc(1)
Clinostomum complanatum a - - 10, 2 + undc (2) - -
Cestoidea
Eubothrium sp.a - - - - 30,4+ 4.4(1-9)
Eubothrium sp. - - 10,1 + undc (1) - 20,23.5+31.8(1-46)
Proteocephalus sp.a 20,1 + 0.0(1-1) - - 10,1 + undc (1) -
Acanthocephala b - - 10,4 + undc (4) - -
Nematoda
Cystidicoloides sp. - - - 10, 1 + undc (1) -
Rhabdochona cascadilla - 60,11.2 +10.7(1-26) - - -
Camallanus sp. a,d - - - 10, 1 + undc (1) -
Crustacea
Salmincola edwardsii 100,10.6 + 8.3(2-27) 60,4.2 + 3.8(1-11) 20,8.5 + 10.6(1-16) 80,1.8 + 1.0(1-4) 100,31.4 + 32.1(3-97) a Larval parasite. c Mathematical operation cannot be defined. (und = undefined) b Could not be identified. d New host record according to Hoffman (1999).
30
Table 8. Prevalence, mean intensity + one standard deviation, and range of intensity of parasite taxa infecting bluegill at Fort McCoy sampling sites.
Parasite W. Sandy Lake Sparta Pond Big Sandy Lake Sandy Lake Stillwell Lake
Monogenea
Ancyrocephalidae 100,28.8 + 31.2(2-118) 100,53.3 + 47.9(1-152) 100,39.2 + 37.0(8-127) 100,19.7 + 20.5(1-65) 20,2.5 + 2.1(1-4)
Actinocleidus + + + + -
Haplocleidus + + + - -
Onchocleidus + + + + -
Syncleithrum + - - - -
Tetracleidus + + + + -
Digenea b 10,6 + und(6)
Clinostomum complanatum a 50,3.2 + 5.3(1-14) - 10,1 + und(1) 20,2.5 + 2.1(1-4) 10,6 + und(6)
Crepidostomum cooperi 25,17 + 15.5(1-32) 30,5.3 + 5.1(1-11) 30,5 + 6.1(1-12) - -
Proterometra sp. 8.3,11+ und(11) - - - -
Neascus sp. a 25,5.3+1.2(4-6) 30,5.7 + 1.7(4-7) 30,1.3 + 0.6(1-2) 50,1.4 + 0.9(1-3) 90,-c(1-tntc)
Posthodiplostomum minimum a 91.7,-c(2-tntc) 70,14.3 + 24.5(3-69) 30,1 + 0.0(1-1) 10, 2 + und(2) 100,-c(1-tntc)
Diplostomulum scheuringi a 16.7,-c(tntc-tntc) - - 80,-c(1-tntc) 60,9.7 + 8.4(2-24)
31
Table 8. Continued.
Parasite W. Sandy Lake Sparta Pond Big Sandy Lake Sandy Lake Stillwell Lake
Cestoidea b 8.3,1 + und(1)
Bothriocephalus cuspidatus - - 60,9.3 + 15.7(1-41) - -
Proteocephalus sp.a 8.3,1 + und(1) - 60,12.7 + 14.5(1-38) 60,1.5 + 8.3(1-3) -
Proteocephalus sp. 8.3,1 + und(1) - - - -
Nematoda
Spinitectus carolini 75,26.4 +17.7(1-52) 30,1.7 + 1.2(1-3) 90,8.0 + 8.4(1-27) 20,1.5 + 0.7(1-2) 90,12.2 + 26.3(2-88)
Camallanus oxycephalus 41.7,2 +1.2(1-4) 10,1 + und(1) - 20,1.5 + 0.7(1-2) 10,1 + und(1)
Crustacea
Achtheres pimelodi - 20,1.5 + 0.7(1-2) - - -
Hirudinea
Myzobdella lugubris 50,1.2 + 0.4(1-2) - - 30,1.3 + 0.6(1-2) - a Larval parasite. b Could not be identified due to lack of distinguishable features. c Could not be determined because parasites were to numerous to count (tntc).
32
Table 9. Parasite prevalence, mean intensity + one standard deviation, and range of intensity of parasite taxa infecting largemouth bass at Fort McCoy sampling sites.
Parasite West Sandy Lake Sparta Pond Big Sandy Lake Sandy Lake
Monogenea
Ancyrocephalidae 100,33.7 + 26.1(3-82) 100,16.7 + 17.3(1-54) 100,36.4 + 18.3(11-55) 100,9.9 + 5.4(3-19)
Actinocleidus - - - +
Haplocleidus + + + +
Onchocleidus + + + +
Syncleithrum + + + +
Digenea
Clinostomum complanatum 25,1 + 0.0(1-1) 43,1.5 + 0.5(1-2) 70,2.9 + 1.2(1-5) 46,3.6 + 4.0(1-10)
Crepidostomum cooperi - 43,21.3 + 35.3(1-90) 10,2.0 + undb(2) 9,2.0 + undb(2)
Neascus sp. a 33,3.5 + 1.9(2-6) 36,6.8 + 7.9(3-21) 50,19 + 22.7(1-58) 27,8.0 + 11.3(1-21)
Posthodiplostomum minimum a 8,-c(tntc) 7,1.0 + undb(1) - 9,-c(tntc)
Diplostomulum scheuringi a - - - 20,-c(4-tntc)
33
Table 9. Continued.
Parasite West Sandy Lake Sparta Pond Big Sandy Lake Sandy Lake
Cestoidea
Bothriocephalus sp.a - - 10,1.0 + undb(1) -
Proteocephalus sp.a 75,14.1 + 14.8(1-46) 14,3.5 + 3.5(1-6) 100,34.6 + 26.0(2-70) 46,24.0 + 25.8(2-65)
Proteocephalus sp. 17,10 + 11.3(2-18) 29,3.3 + 3.2(1-8) - -
Acanthocephala
Neoechinorhynchus tenellus d 92,14.5 + 7.5(2-26) 14,3.0 + 2.8(1-5) - 64,1.4 + 0.8(1-3)
Nematoda
Spinitectus carolini 33,3 + 1.8(1-5) 29,1.3 + 0.5(1-2) 10,1.0 + undb(1) -
Camallanus oxycephalus 8,1.0 + undb(1) - - 9,1.0 + undb(1)
Contracaecum sp.a 58,1.1 + 0.5(1-2) - - 9,1.0 + undb(1)
Hirudinea
Myzobdella lugubris 8,1.0 + undb(1) - - - a Larval parasite. b Mathematical operation cannot be defined. c Could not be determined because parasites were to numerous to count (tntc). d New host record according to Hoffman (1999).
34
Figure 6. Similarity dendrogram of parasite communities infecting largemouth bass at Fort McCoy. The horizontal gray line represents 70% similar evaluation line. On the horizontal axis, the first series of numbers represents the sampling site (09-157: West Sandy Lake, 09-164: Sparta Pond, 09-179: Big Sandy Lake, 09-199: Sandy Lake), LMB refers to largemouth bass, and the final number represents individual largemouth bass at each sampling location.
35
Brook trout-Nine parasite genera were recovered from the brook trout examined from five sampling sites at Fort McCoy (Table 7, Fig. 1). All parasite genera recovered
have been previously reported from brook trout with the exception of Camallanus sp. recovered from South Fork of the La Crosse River. This is a new host record for
Wisconsin as well as North America (Hoffman 1999). The number of parasites species infecting brook trout ranged from 0 to 3, with most brook trout (>50%) infected with one parasite species, primarily Salmincola edwardsii (Table 7, Fig. 7). All brook trout from
Silver Creek and East Silver Lake were infected with at least one parasite genus. One fish from South Fork of the La Crosse River and one fish from East Silver Lake were infected with three parasite genera (Fig. 7).
Abundance of all parasite species from brook trout was significantly different between bodies of water (One-way ANOVA, p < 0.05). East Silver Lake was significantly higher in total parasite abundance than other sampling sites (Scheffe’s, p <
0.05) (Fig. 8a).
9 Silver Creek 8 Tarr Creek Sparta Creek 7 S. Fork Lax River E. Silver Lake 6
h 5
4 No. of Fis of No.
3
2
1
0 0123 No. of Parasite Species
Figure 7. Distribution of the number of parasite taxa infecting brook trout at the Fort McCoy sampling sites.
36
Abundance of Salmincola edwardsii was significantly different between bodies of water
(One-way ANOVA, p < 0.05). East Silver Lake was significantly higher in abundance of
S. edwardsii from Tarr Creek, Sparta Creek, and South Fork of the La Crosse River
(Scheffe’s, p < 0.05) (Fig. 8b). Clinostomum complanatum, adult Eubothrium sp., acanthocephalans, Cystidicoloides sp., Rhabdochona cascadilla, and Camallanus sp. were recovered from only one body of water (Table 7). Host size has been suggested to influence parasite abundance. No correlation was observed between host size and parasite abundance (Fig. 8c).
Figure 8. Parasite abundance (+ one standard error) infecting brook trout at the Fort McCoy sampling sites. A. All parasite species; B. Salmincola edwardsii; C. Mean length of brook trout examined for parasites from the Fort McCoy sampling sites.
37
Bluegill-Seventeen parasite genera were recovered from bluegill from five bodies
of water on Fort McCoy (Table 8, Fig. 1). All parasite genera recovered previously have
been reported from bluegill (Hoffman 1999). Ten of the parasite genera were found at
more than one sampling site and four genera were found at all five sampling sites (Table
8). The number of parasite species infecting all bluegill ranged from 1 to 9 parasite
species, with most fish (>70%) infected with 3 to 5 parasite species (Fig. 9).
Abundance of all parasites infecting bluegill was not significantly different
between sampling sites (One-way ANOVA, p > 0.05) (Fig. 10a). Abundance of
Spinitectus carolini was significantly different between sampling sites (One-way
ANOVA, p < 0.05). Sparta Pond and Sandy Lake were significantly lower in S. carolini abundance from West Sandy Lake, Big Sandy Lake, and Stillwell Lake (Scheffe’s p <
0.05) (Fig. 10b). Abundance of ancyrocephalids was significantly different between sampling sites (One-way ANOVA, p < 0.05). Stillwell Lake was significantly lower in
Ancyrocephalidae abundance from all other bodies of water (Scheffe’s, p < 0.05) (Fig.
10c).
7
W. Sandy Lake 6 Sparta Pond Big Sandy Lake 5 Sandy Lake Stillwell Lake 4
3 No. of Fish Fish of No.
2
1
0 123456789 No. of Parasite Species
Figure 9. Distribution of the number of parasite taxa infecting bluegill at Fort McCoy sampling sites.
38
Abundance of Posthodiplostomum minimum was significantly different between sampling sites (One-way ANOVA, p < 0.05). West Sandy Lake and Stillwell Lake were significantly higher in P. minimum abundance from Sparta Pond, Big Sandy Lake and
Sandy Lake (Scheffe’s p < 0.05) (Fig. 10d). Abundance of larval Proteocephalus sp. was
significantly different between sampling sites (One-way ANOVA,p < 0.05). Big Sandy
Lake was significantly different in Proteocephalus sp. abundance from West Sandy Lake
(Scheffe’s p < 0.05) (Fig. 10e). No correlation was observed with respect to host size and
parasite abundance (Fig. 10f).
Figure 10. Parasite abundance (+ one standard error) infecting bluegill at the Fort McCoy sampling sites. A. All parasite species; B. Spinitectus carolini; C. Ancyrocephalidae; D. Posthodiplostomum minimum; E. Proteocephalus sp.; F. Mean length of bluegill examined for parasites from the Fort McCoy sampling sites.
39
Largemouth bass-Sixteen parasite genera were recovered from the largemouth
bass examined from four sampling sites on Fort McCoy (Table 9, Fig. 1). The recovery
of Neoechinorhynchus tenellus from largemouth bass at West Sandy Lake, Sparta Pond,
and Sandy Lake is a new host record for Wisconsin and North America (Hoffman 1999,
Amin and Muzzall 2009). All other parasites recovered have previously been reported
from largemouth bass (Hoffman 1999). Eleven of the parasite genera were recovered
from more than one sampling site and four parasite genera were recovered at all sampling sites (Table 9). The number of parasite species infecting all largemouth bass ranged
from 1 to 7 parasite species, with more than 70% infected with 2 to 4 parasite species
(Fig. 11).
Abundance of all parasites infecting largemouth bass was not significantly different between bodies of water (One-way ANOVA, p > 0.05) (Fig. 12a). Abundance
of Ancyrocephalidae was significantly different between sampling sites (One-way
ANOVA, p < 0.05). Sandy Lake was significantly lower in Ancyrocephalidae abundance
from all other bodies of water (Scheffe’s, p < 0.05) (Fig. 12b). Abundance of larval
Proteocephalus sp. was significantly different between sampling locations (One-way
9 W. Sandy Lake 8 Sparta Pond 7 Big Sandy Lake Sandy Lake
. 6
5
4 No. of Fish No. of Fish 3
2
1
0 1234567 No. of Parasite Species
Figure 11. Distribution of the number of parasite taxa infecting largemouth bass at the Fort McCoy sampling sites.
40
ANOVA, p < 0.05). Big Sandy Lake was significantly higher in larval Proteocephalus
sp. abundance from all other bodies of water (Scheffe’s, p < 0.05) (Fig. 12c).
Abundance of Neoechinorhynchus tenellus was significantly different between bodies of
water (Two-way ANOVA, p < 0.05). West Sandy Lake was significantly higher in
Neoechinorhynchus tenellus abundance from Sparta Pond and Sandy Lake (Scheffe’s, p <
0.05) (Fig.12d). N. tenellus was absent at Big Sandy Lake. No correlation was observed
with respect to host size and parasite abundance (Fig. 12e).
Figure 12. Parasite abundance (+ one standard error) infecting largemouth bass at the Fort McCoy sampling sites. A. All parasite species; B. Ancyrocephalidae; C. Proteocephalus sp.; D. Neoechinorhynchus tenellus; E. Mean length of largemouth bass examined for parasites from the Fort McCoy sampling sites.
41
Host comparison-Fourteen parasite genera exhibited host overlap between
bluegill and largemouth bass (Tables 8-9). Abundance of total parasite infection,
Ancyrocephalidae, and Posthodiplostomum minimum (data not shown) infecting
largemouth bass and bluegill was not significantly different between host species or
sampling sites (Two-way ANOVA, p > 0.05) (Fig. 13a-b). Abundance of larval
Proteocephalus sp. was significantly different between host species and sampling
location (Two-way ANOVA, p < 0.05). Big Sandy Lake was significantly higher in
larval Proteocephalus sp. abundance from all other sampling sites (Scheffe’s, p < 0.05)
(Fig. 13c). Abundance of Spinitectus carolini was significantly different between host
species and sampling location (Two-way ANOVA, p < 0.05). West Sandy Lake was
significantly higher in S. carolini abundance from all other bodies of water (Scheffe’s,
p < 0.05) (Fig. 13d).
Figure 13. Parasite abundance (+ one standard error) infecting bluegill and largemouth bass at the Fort McCoy sampling sites. A. All parasite species; B. Ancyrocephalidae; C. Proteocephalus sp.; D. Spinitectus carolini.
42
Diet Over 85% of the brook trout, brown trout, bluegill and largemouth bass had
identifiable food items in their stomachs. The brook trout had the most diverse diet
while largemouth bass and brown trout had the least diverse diet (Fig. 14). Prey items representing vertebrates and invertebrates residing in terrestrial and aquatic communities
were recovered from all fish species.
Brown trout-The most common prey items in the stomach of the brown trout were
larval trichopterans and amphipods (Fig. 14). Forty-six percent of the brown trout
consumed trichopterans from the family Brachycentridae. Other larval trichopterans
were represented by the family Limnephilidae and unidentifiable specimens. The brown
trout at Tarr Creek had a more diverse diet, consuming representatives from 11 taxonomic orders, while the brown trout at Silver Creek had a less diverse diet, consuming representatives from 4 taxonomic orders (Table 10).
Brook trout-The most common prey items in the stomach of the brook trout were larval trichopterans, amphipods, dipterans, and isopods (Fig. 14). The most common trichopterans consumed by the brook trout were representatives of the families
Limnephilidae (37%) and Brachycentridae (28%). The families Hydropsychidae,
Phryganeidae, Leptoceridae, and Hydroptilidae were also represented, but at low
frequencies. The most common dipterans consumed by the brook trout were
representatives of the family Chironomidae (50%). The families Athericidae and
Simuliidae were also represented, but at low frequencies. The Odonata were represented
by the family Calopterygidae, and the Hemiptera were represented by the family
Corixidae. The brook trout at Sparta Creek had the most diverse diet, consuming
43
70
60 Largemouth Bass Bluegill 50 Brook Trout Brown Trout 40
30 % Consumption Consumption % 20
10
0
s l s a i a a t t a a a a a e d a a a i a a a i r a a a e r r r r i i c r t r n a l c d v t d d r e e e e d d i e e a l n a e t e e d s t t t o r e t t o o o i o s a s n c h t p p p p p a t o p p c m n p p p c n i i v a i o o c i a e I o o o i I o o a o a l l h r d d a h r r m l D e m s c m e B r m M c a e p t a c l I a a e e l r e i O s d T i g i A t t o r m m a o r e H D C y M a N n t e C F T a u s A G h H l M e q p r P r A E e
T
Figure 14. Diet composition of four fish species from all sampling sites at Fort McCoy.
44
Table 10. Percentage of brown trout with each prey item in stomach contents at each sampling site.
Food item Silver Creek Tarr Creek
Aquatic insects* - 70
Terrestrial insects 29 10
Diptera - 40
Trichoptera 79 20
Ephemeroptera - 20
Plecoptera 7 30
Coleoptera - 10
Odonata - 10
Amphipoda - 90
Isopoda - 30
Decapoda 21 -
Teleostei - 40
Gastropoda - 10
Plant material 7 10
*Insects not identifiable beyond the class level.
representatives from 12 taxonomic orders, while the trout at Silver Creek had the least
diverse diet, consuming representatives from 3 taxonomic orders (Table 11).
Bluegill-The most common prey items in the stomach of the bluegill were larval
dipterans, cladocerans, larval ephemeropterans, amphipods, larval trichopterans, and
larval odonates (Fig. 14). All bluegill that consumed larval dipterans had at least one
representative of the Chironomidae family in their stomachs. The dipteran families
45
Ceratopogonidae and Athericidae were also represented at low frequencies. The most common larval ephemeropteran (>50%) consumed by the bluegill were representatives of the family Caenidae. The families Ephemeridae, Siphlonuridae, and Ephemerellidae were represented, but at low frequencies. The most common larval trichopteran (>63%) consumed by bluegill were representatives of the family Limnephilidae. The families
Phryganeidae, Brachycentridae, and Leptoceridae were also represented, but at low frequencies. The Odonata were represented by the families Corduliidae and
Coenagrionidae, and unidentifiable specimens due to degradation. Bluegill at Sparta
Pond had the most diverse diet, consuming representatives from 12 taxonomic orders, while the bluegill at Stillwell Lake consumed representatives from 5 taxonomic orders
(Table 12).
Largemouth bass-The most common prey item consumed by the largemouth bass were larval odonates (Fig. 14). The most common suborder represented were Anisoptera
(81%), with representatives from the families Cordulidae, Aeshnidae, and Libellulidae.
The diet of the largemouth bass was variable between bodies of water (Table 13). The largemouth bass at Sparta Pond had the most diverse diet, consuming representatives from 10 taxonomic orders, while the bass at Sandy Lake had the least diverse diet consuming representatives from 3 taxonomic orders (Table 13).
46
Table 11. Percentage of brook trout with prey item in stomach contents at each sampling site.
Food item Silver Creek Tarr Creek Sparta Creek S. Fork La Croose River E. Silver Lake
Aquatic insects* 30 30 20 - -
Terrestrial insects 20 - - 10 -
Diptera - 60 10 60 10
Megaloptera - - 10 - -
Trichoptera 90 70 50 90 20
Ephemeroptera - 10 10 30 -
Coleoptera - 10 10 10 -
Odonata - - 40 - -
Hemiptera - - - 10 20
Amphipoda 20 60 10 - -
Isopoda - - 70 40 -
Decapoda - - 10 - -
Bivalvia - - 20 - -
Teleostei - 30 - - -
Gastropoda - 30 20 - 40
47
Table 11. Continued.
Parasite Silver Creek Tarr Creek Sparta Creek S. Fork La Crosse River E. Silver Lake
Mammalia 10 - - - -
Formicidae - 10 - - -
Arachnida - 10 - - -
Plant material - 10 20 - - *Insects not identifiable beyond the class level.
48
Table 12. Percentage of bluegill with each prey item in stomach contents at each sampling site.
Food item W. Sandy Lake Sparta Pond Big Sandy Lake Sandy Lake Stillwell Lake
Aquatic insects* 25 - 40 40 -
Terrestrial insects 25 - 50 - -
Diptera 50 80 30 30 10
Trichoptera 17 90 - - -
Ephemeroptera 42 6 30 - -
Coleoptera 8 10 - 10 10
Odonata 25 40 20 10 10
Hemiptera 8 - 10 10 -
Amphipoda 33 100 - - -
Isopoda - 90 - - -
Decapoda - - - 10 -
Bivalvia 17 30 10 - -
Teleostei - - 10 - -
Gastropoda 8 20 - 10 -
49
Table 12. Continued.
Food item W. Sandy Lake Sparta Pond Big Sandy Lake Sandy Lake Stillwell Lake
Cladocera - 20 20 60 60
Nematoda - 10 - - -
Plant Material - - - 10 50
Hydracarina 17 20 - - - *Insects not identifiable beyond the class level.
50
Table 13. Percentage of largemouth bass with each prey item in stomach contents at each sampling site.
Food item West Sandy Lake Sparta Pond Big Sandy Lake Sandy Lake
Aquatic insects* - - 20 18
Terrestrial insects 33 - 10 -
Diptera - 14 - -
Trichoptera - 36 - -
Ephemeroptera 8 14 - -
Coleoptera 17 7 20 9
Odonata 42 57 50 27
Hemiptera 33 7 - -
Amphipoda - 14 - -
Decapoda - 7 - -
Teleostei 17 7 10 9
Gastropoda 8 7 - -
Mammalia - - 20 - *Insects not identifiable beyond the class level.
51
Discussion
There were no target bacterial or viral pathogens detected in the fish screened at
Fort McCoy Military Installation (Fort) despite historical records of target pathogens in
the surrounding areas. The absence of target pathogens could be a result of relatively
unspoiled environment at the Fort, limited sample size, small host populations with an
acquired immunity which were unable to support the pathogens (Anderson and May
1979), or viruses were undetected due to low viral titers (Hope et al. 2010). Hope et al.
(2010) found qRT-PCR was 100 times more sensitive than tissue cell culture for detecting VHSV in tissue samples, when viral titers were low. Further research could investigate if fish at Fort McCoy have specific antibodies of target pathogens (suggesting previous exposure) or investigate the sensitivity of tissue cell culture methods to PCR
assays. However, tissue cell culture would still be an important tool during surveys for
detecting novel viruses.
This was the first time the fish parasite community at Fort McCoy was evaluated.
The number and types of species parasitizing brook trout, bluegill, and largemouth bass
was expected and is similar to previous reports (Esch 1971, Hoffman 1999, Muzzall
2007). Some parasites recovered from Fort fish were new host records: Camallanus sp.
(brook trout) and Neoechinorhynchus tenellus (largemouth bass). The recovery of
Camallanus sp. could be due to accidental infection because only one fish at one locality
was infected.
52
The fish examined in this study did not show signs of excessive parasite burden and exhibited little abnormal gross pathology. Excessive mucus on the gills was observed with heavy infections of S. edwardsii and ancryrocephalids. At Big Sandy Lake some of the largemouth bass infected with larval Proteocephalus sp. exhibited adhesions in the peritoneal cavity. Elsayed and Faisal (2008) reported similar pathology in largemouth bass infected with larval Proteocephalus sp. Esch et al. (1975b) suggested temperature and host’s hormones stimulated Proteocephalus sp. plerocercoids to migrate from gonadal and visceral tissue into the gastro-intestinal tract in order to develop into the adult stage. This migration may have caused the adhesions in the largemouth bass.
Parasites and hosts generally evolve together. Since brown trout were imported into Wisconsin as eggs, there was little risk of introducing non-native parasites. In native habitats, brown trout are infected with more parasite species. Dorucu et al. (1995) reported an average of 5 parasite species in Central Scotland and Quilichini et al. (2007) reported an average of 3 parasite species in Corsica, France. In this study only
Rhabdochona cascadilla was recovered from brown trout at Tarr Creek. R. cascadilla is a generalist nematode reported from 38 fish genera representing 14 families in North
America (Hoffman 1999). This would explain its ability to infect an introduce species like brown trout.
Parasite communities are shaped by abiotic and biotic factors of the ecosystem
(Bush et al. 2001). The Fort sampling sites are in close proximity and probably affected by similar external climatic and environmental factors (e.g. precipitation, temperature, etc.). Within each water body, internal abiotic factors could be variable (e.g. flow, surface area, etc.). Biotic influences include host behavior, availability of intermediate
53
hosts, host density, and host diet have been shown to affect parasite communities (Wilson
et al.1996, Arneberg et al. 1998, Morand and Poulin 1998, Poulin and Valtonen 2002,
Johnson et al. 2004). This is especially true for parasites with indirect life cycles; the
intermediate host must be available and in close proximity or be consumed by the next
host.
Water type, diet and sampling time may have influenced parasite diversity of
brook trout more than host density. South Fork La Crosse River and Sparta Creek had
the greatest parasite species richness but Sparta Creek had nearly double the number of
brook trout per mile. Increased stream order of South Fork La Crosse River could have
provided more diverse habitats for brook trout and a more diverse intermediate host
community, thus potentially resulting in more parasite species. For example, C. fausti
recovered from this location requires three intermediate hosts to complete its life cycle
(Hoffman 1999). Brook trout from Sparta Creek had a more diverse diet and higher
parasite species richness than Silver Creek, where a less diverse diet was observed. At
East Silver Lake sampling time seemed to have influenced higher S. edwardsii
abundance. At this site, fish were collected in June, whereas other brook trout locations
were sampled in October.
Bluegill parasite diversity and abundance may have been influenced by lake size, host density, and sampling time. Sparta pond had the highest density of bluegill per acre
and highest mean intensity of ancyrocephalids. Arneberg et al. (1998) demonstrated
mammalian host density and intestinal nematode abundance were positively correlated.
In particular, high host density is crucial for transmission of monogenean parasites with
direct life cycles. The infective oncomiracidia have limited amount of time to locate a
54
host (Bush et al. 2001). Sampling time may have influenced abundance of
ancyrocephalids from Stillwell Lake. Bluegill from Stillwell Lake were collected in
September and infestations could have been lower than those sampled in the summer due
to ancyrocephalids exhibiting seasonal trends. Rawson and Rogers (1972) reported low
abundance of Actinocleidus fergusoni (Ancyrocephalidae) infecting bluegill in the winter
months compared to summer.
The significantly lower abundance of P. minimum and the higher abundance of
larval Proteocephalus sp. at Big Sandy could be a result of bluegill habitat and diet
preference. Big Sandy Lake has the greatest surface area and is the deepest of the lakes
sampled. Bluegill were possibly collected in habitats were intermediate hosts of larval
Proteocephalus sp. reside and not in close proximity to Physa sp., the intermediate host
of P. minimum. Wilson et al. (1996) demonstrated bluegill collected from open water
had a higher abundance of Proteocephalus sp. and lower abundance of P. minimum than
bluegill collected from the littoral zone. Future studies should record habitat type at time
of fish collection.
Host density, size of water body and diet may have influenced parasite
communities of largemouth bass at Fort McCoy. Sandy Lake had the lowest number of
largemouth bass per acre and a significantly lower intensity of ancyrocephalids. Larval
Proteocephalus sp. infecting the largemouth bass at Big Sandy Lake were likely a result
of similar influences as those observed for bluegill at this location. The largemouth bass
could be ingesting more copepods and also consuming infected bluegill (second
intermediate host). Higher abundance of N. tenellus infecting largemouth bass at West
55
Sandy Lake could have resulted from largemouth bass consuming more crustacean intermediate hosts or consuming paratenic hosts (e.g. bluegill) of N. tenellus.
Freeland (1983) reported parasite communities in sympatric hosts usually do not
carry the same set of parasite species, and if there is overlap, the parasite prevalence
would vary between host species. In this study there was high overlap of parasite species between the bluegill and largemouth bass. There were no significant differences in abundance of P. minimum and ancyrocephalids in the two host species. This parasite overlap is probably due to these parasite species exhibiting limited host specificity. Both of these parasite taxa have been reported from many centrarchid species. These findings contradict Freeland (1983). However, two other parasites, Proteocephalus sp. and S.
carolini, were significantly different in infection between hosts. Diet of bluegill and
largemouth bass likely affected the significantly higher abundance of S. carolini in
bluegill. Bluegill in this study consumed more of the intermediate hosts of S. carolini
(Jilek and Crites 1982b) than the largemouth bass.
Locations with the highest density of brook trout, bluegill, and largemouth bass
had the most variability in diet. The variability could be a due to more diverse
invertebrate community available as prey, which can support a greater fish density, or the
fish are less selective at these locations to reduce intra and inter-specific competition.
Schindler et al.(1997) showed individual largemouth bass exhibited a more consistent
diet at higher fish densities. This consistency was not reflective in the diet of the bass at
the population level. They suggested this was an adaptive behavior of each fish to reduce
intra-specific competition.
56
It is rare to conduct diet studies in conjunction with parasite communities studies, and doing so can uncover relationships that might go undetected (Hernandez and
Sukhdea 2008). Examining the stomach contents provided a picture of the dietary preferences of each fish prior to collection, but did not provide a complete depiction of the diet. This study demonstrated that parasites could be used to determine prey items.
For example, few brook and brown trout had larval ephemeropterans, the intermediate host of R. cascadilla (Barger and Janovy 1994), in their stomach contents at Tarr Creek.
R. cascadilla prevalence was high at this location, thus, we know more trout at this location consumed larval ephemeropterans.
Additionally, no copepods were recovered in the stomach contents of bluegill or largemouth bass, but infection of Proteocephalus sp. suggests these fish consumed copepods, probably as juvenile fish (Esch et al. 1975b, Pracheil and Muzzall 2009).
Similar conclusions can be made about bluegill infected with S. carolini and consumption of larval ephemeropterans at Sandy and Stillwell Lakes. Examining parasites with indirect life cycles provides insight about food choices throughout the fish’s lifetime.
However, in order to link parasite community to host’s diet, it is necessary to understand parasite life histories and the intermediate hosts necessary to complete the parasite life cycle. Additionally, using long-term parasite and diet studies together could provide insight into alternative and potential intermediate hosts of parasites whose life histories are not well understood.
Several new host records were found during the parasite survey at Fort McCoy, suggesting that surveys are necessary for establishing baselines, monitoring trends and detecting invasive species. Additionally, this survey provided insights about factors
57
affecting the parasitic community structure, life histories of hosts, ecosystem fauna and parasitism between sympatric hosts.
Museum specimens from Harold W. Manter Laboratory of Parasitology (Lincoln,
NE) should be requested for morphometric comparison of Fort McCoy specimens to museum specimens. Additionally, depositions should be made to Harold W. Manter
Laboratory and/or the United States National Parasite Collection (USNPC) (Beltsville,
MD). Further research should focus on factors that could shape Fort McCoy’s parasite communities. Otoliths were collected and will be processed at a later date in order to evaluate if age plays a role in structuring the parasite communities. Future studies should continue to investigate the roles of host density, diet, water size, host availability, and season on the parasite community at Fort McCoy. Additionally, these studies should be designed to include a greater sample size, additional fish and invertebrate species, habitat information at time of collection (i.e.: benthos, littoral, open water), and seasonal sampling regimes. This would provide clarity on abiotic and biotic factors structuring parasite community. Fish should be routinely screened for viral and bacterial pathogens, which could assist in initiating management and control measures at Fort McCoy if a serious pathogen was detected.
The parasite communities infecting brown trout, brook trout, bluegill, and largemouth bass were different between bodies of water, with some parasite species unique to each location. Generally, an ecosystem rich in parasites species is considered a healthy community (Hudson et al. 2006), especially if the parasites utilize indirect life cycles that require different intermediate hosts. This is because the host populations are healthy enough to support a parasite community. Based on the preceding parasite
58
community analysis, Fort McCoy’s aquatic community could be called a healthy
community. This is supported by absence of viral and target bacterial pathogens in the
fish at Fort McCoy. These fish could potentially be used as wild brood stock for
hatcheries that are propagating fish for other localities. However, caution should be
taken when transferring fish between localities to minimize changes in parasite community and disease transfer. Some parasites can serve as vectors of viral pathogens
(e.g. Myzobdella lugubris can vector VHSV), thus consideration should be taken when managing an ecosystem. This would maintain biological integrity and minimize anthropogenic changes to the parasite community and the ecosystem.
59
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APPENDIX A.
FLOW CHART FOR IDENTIFICATION OF BACTERIAL PATHOGENS FROM
USFWS AND AFS-FHS (2007) 69
APPENDIX B
RECIPE FOR PREPARING PEPSIN AND TRYPSIN DIGEST SOLUTIONS
0.5% Pepsin 0.5% Trypsin
1 L of water 1 L of water 5.0 g Pepsin 0.20 g EDTA 5 ml HCl 8.00 g NaCl 0.20 g KCl 0.20 g KH2PO4 1.15 g NaHPO4 5.00 g Trypsin
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APPENDIX C
PHOTOMICROGRAPH OF MYXOBOLUS CEREBRALIS SPORES (COURTESY U.S.
FISH AND WILDLIFE SERVICE-B.LASEE)
USFWS
USFWS
73