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Fish and Wildlife Disease

Researchers bring understanding to how diseases interact with their fish and wildlife hosts.

Microbiology

Fish

Browse samples of USGS research about fish and wildlife disease and fish. For related links, see Related Links and References at the bottom of page.

Salmon with clinical signs of Bacterial Kidney Disease (BKD). Photo credit: USGS Western Fisheries Research Center

Adaptation to Bacterial Kidney Disease
(Purcell, Elliott)

Aphanizomenon flos-aquae, as viewed at 100x magnification. Photo credit: Barry H. Rosen, USGS

Cyanotoxins in Klamath Lake
(Rosen)

Isolates of IHNV from the western US fall into three major genetic groups or clades that typically correlate with host and geographic range.

Emerging Virus Threat to Fish in Western Washington
(Kurath)

Northern snakehead (Channa argus). Photo credit: USGS, courtesy USGS Southeast Ecological Science Center Photo Gallery

Northern Snakehead: Risk of Exotic Pathogen Introduction (Iwanowicz, Densmore)

A TEM image of pallid sturgeon iridovirus (PSIV); Photo credit: Linda Beck, Bozeman Fish Technology Center, US Fish and Wildlife Service

Pallid Sturgeon Iridovirus (PSIV) (Iwanowicz)

Mycobacteriosis lesions in striped bass. Photo courtesy of the Maryland Department of Natural Resources

Striped Bass: Zoonotic Mycobacteriosis and Adaptive Fishery Managment (Panek)

Photo: Fulbright Scholar Michele Penaranda. Credit: Gael Kurath/USGS.

Efficacy of DNA Vaccines for an Important Fish Virus (Kurath)

Paenibacillus thiaminolyticus. Photo credit: Catherine A. Richter, USGS Columbia Environmental Research Center

Q-PCR Detection of Bacterial Sources of Thiaminase I
(Richter)

A laboratory test to identify the bacteria from the mussels. Photo credit: USGS

Quarantine Mussels to Prevent Disease Transmission to Brook Trout (Starliper)

Two students using a ruler-board to measure and collect data from mussel specimens. The data collected include length, weight, width, depth, area inside valves, weight of soft tissues, etc. Photo credit: USGS

Recovering Bacteria from Mussels using Non-Destructive Procedures (Starliper)

Brook trout netted. Photo Credit: Shenandoah National Park

Trout: Pathogens and Fish Stocking Practices in National Parks (Panek)

Great Lakes. Photo credit: Jeff Schmaltz/NASA

Viral Hemorrhagic Septicemia Virus in the Great Lakes
(Winton)

Heart of adult Chinook salmon showing signs of Ichthyophonus infection. Photo credit: R. Kocan, University of Washington

Warming Climate Can Affect Fish Health (Winton)

Photo: Rainbow Trout. Credit: Gael Kurath/USGS.

Pathogen Fitness (Kurath)


Pathogen Fitness and Virulence of a Fish Virus
Photo: Rainbow Trout. Credit: Gael Kurath/USGS.
Photo: Rainbow Trout. Credit: Gael Kurath/USGS.

In a latest issue of The Journal of Virology, researchers from the USGS Western Fisheries Research Center and the University of Washington examined the relationship between pathogen fitness and virulence using an important fish virus, Infectious hematopoietic necrosis virus (IHNV). Pathogen fitness and virulence are typically quantified by measuring only one or two pathogen fitness traits. In this study, the researchers independently quantified four viral infection cycle traits, namely, host entry, within-host replication, within-host coinfection fitness, and shedding. The researchers report that viral fitness was independently regulated by each of the traits examined, with the largest impact on fitness being provided by within-host replication. The results are thus congruent with the assumption that virulence and within-host replication are correlated but suggest that infection cycle fitness is complex and that replication is not the only trait associated with virulence. For more information, visit http://www.ncbi.nlm.nih.gov/pubmed/21307204.

For more information, contact Gael Kurath, USGS Western Fisheries Research Center.

Additional link:

In Vivo Fitness Associated with High Virulence in a Vertebrate Virus Is a Complex Trait Regulated by Host Entry, Replication, and Shedding (pdf)

 

 

 

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Efficacy of DNA Vaccines for an Important Fish Virus
Photo: Fulbright Scholar Michele Penaranda. Credit: Gael Kurath/USGS.
Photo: Fulbright Scholar Michele Penaranda. Credit: Gael Kurath/USGS.

Researchers from the USGS Western Fisheries Research Center, University of Washington and Clear Springs Food Inc. have reported their findings on cross-protective efficacy of DNA vaccines for the fish virus Infectious hematopoietic necrosis virus (IHNV). This study demonstrated that rainbow trout mount a broad immune response following vaccination that can cross-protect against different IHNV strains. IHNV causes significant mortality in both wild and cultured salmon and trout in North America, Asia and Europe. The abstract can be found at http://www.ncbi.nlm.nih.gov/pubmed/21385613.

For more information, contact Gael Kurath, USGS Western Fisheries Research Center.

 

 

 

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Adaptive Potential of Chinook Salmon to Resist Bacterial Kidney Disease (BKD)
Salmon with clinical signs of Bacterial Kidney Disease (BKD). Photo credit: USGS Western Fisheries Research Center
Salmon with clinical signs of Bacterial Kidney Disease (BKD). Photo credit: USGS Western Fisheries Research Center
Image Gallery

Mass mortality events due to infectious disease agents in wild fish populations are troubling, but it is the long-term, population-level consequences which may be of more significance. Basic evolutionary theory predicts that populations with sufficient genetic variation will adapt in response to pathogen pressure. Chinook salmon were introduced into Lake Michigan in the late 1960s from a Puget Sound population (Washington State). In the late 1980s, collapse of the forage base in Lake Michigan was thought to contribute to die-offs of Chinook salmon due to Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD). Evidence from our laboratory demonstrates that Chinook salmon from Lake MI, Wisconsin have greater survival following R. salmoninarum challenge relative to several Pacific Northwest populations, including its progenitor population (Purcell et al., 2008). A collaborative study between scientists at the Western Fisheries Research Center (USGS) and the Northwest Fisheries Science Center (NOAA Fisheries) seeks to characterize the genetic basis for survival following Renibacterium salmoninarum infection in a Lake MI population of Chinook salmon. We have hypothesized that pathogen-driven selection during the Lake MI BKD epidemics enhanced the ability of the Wisconsin population to resist or tolerate R. salmoninarum infections. If true, a possible trade-off to the fitness gains achieved by selection can be a reduction in the overall genetic variation at the trait, thereby limiting future evolutionary potential. In this study, we are comparing the genetic variation controlling R. salmoninarum survival in the contemporary Wisconsin and Washington Chinook salmon populations. We are also determining if higher R. salmoninarum survival of the Wisconsin population is a stable trait when an environmental parameter shifts, a measure of phenotypic plasticity. The ability to respond and adapt to a changing environment is critical for long-term sustainability of any population. This study is funded by the Great Lakes Fishery Trust.

Related Publications:

Maureen K. Purcell, Anthony L. Murray, Anna Elz, Linda K. Park, Susan V. Marcquenski, James R. Winton, Stewart W. Alcorn, Ronald J. Pascho, and Diane G. Elliott. 2008. Decreased Mortality of Lake Michigan Chinook Salmon after Bacterial Kidney Disease Challenge: Evidence for Pathogen-Driven Selection? Journal of Aquatic Animal Health, 20:4, 225-235. doi: 10.1577/H08-028.1 (online abstract of journal article External link)

For more information, contact Maureen K. Purcell or Diane G. Elliott at the Western Fisheries Research Center.

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Cyanotoxins in Klamath Lake
Microcystis spp. Photo credit: Barry H. Rosen, USGS
Microcystis spp.  This organism cannot “fix” atmospheric nitrogen. Photo credit: Barry H. Rosen, USGS
Image Gallery
Aphanizomenon flos-aquae. Photo credit: Barry H. Rosen, USGS
Aphanizomenon flos-aquae. Photo credit: Barry H. Rosen, USGS
Aphanizomenon flos-aquae, as viewed at 100x magnification. Photo credit: Barry H. Rosen, USGS
Aphanizomenon flos-aquae, as viewed at 100x magnification.  Note the cluster of filaments that give it the appearance of grass clippings.  Color is normally grass-green.  This organism can “fix” atmospheric nitrogen. Photo credit: Barry H. Rosen, USGS
Image Gallery

A collaborative project with the several USGS Science Centers, we are exploring the known toxin-producing species of cyanobacteria in Klamath Lake, Oregon.  The endangered Lost River and shortnose suckers lose a great percentage of their population in the first year of life.  Two species of cyanobacteria are suspect:  Aphanizomenon flos-aqua and Microcystis aeruginosa.  Microcystis produces the toxin microcystin that causes liver damage that may be affecting these fish.  Preliminary results indicate that the young suckers are consuming invertebrates, which in turn consume cyanobacteria as their food source.

For more information, contact Barry H. Rosen, Florida Integrated Science Center.

 


Emerging Virus Threat to Fish in Western Washington
Phylograms created using Bayesian analysis of sequence data showing the genetic relationships of isolates of IHNV.
Fig 2.
Isolates of IHNV from the western US fall into three major genetic groups or clades that typically correlate with host and geographic range.
Fig 1. Larger View

A new strain of infectious hematopoietic necrosis virus (IHNV) that is highly lethal for steelhead trout has emerged in rivers of the Olympic Peninsula in Washington State. The M-D strain of IHNV is believed to have originated in the upper Columbia River watershed in the late 1970s where it has continued to evolve and to move downriver to affect additional stocks. The spread of M-D IHNV to geographically separate watersheds in the Olympic Peninsula constitutes a risk to genetically distinct stocks of steelhead trout that are co-managed by tribal, state and federal agencies. In order to understand the epidemiology of M-D IHNV and the risks posed to wild stocks of salmonids in affected watersheds, data on ecological, physical and anthropogenic factors will be compared with sequence analysis (Figure 1) of new isolates of IHNV from the region and elsewhere.

For more information contact Gael Kurath, Western Fisheries Research Center, Seattle, WA.

Figure 1. Isolates of IHNV from the western US fall into three major genetic groups or clades that typically correlate with host and geographic range. The "U" clade is found predominantly in sockeye salmon throughout a wide area of North America, while the "L" clade is principally found in Chinook salmon in Northern California or Southern Oregon. The "M" clade was originally discovered in rainbow trout in the Hagerman Valley of Southern Idaho, but has since spread and become established in steelhead trout in the lower Columbia River.
Figure 2. Phylograms created using Bayesian analysis of sequence data showing the genetic relationships of isolates of IHNV. The new M-D isolates from the Olympic Peninsula are on a branch indicated with an orange arrow.

 

 


Investigating the Nature of a Putative Virus Isolated from the Introduced Species, the Northern Snakehead (Channa argus), Present in the Chesapeake Bay Watershed
Northern snakehead (Channa argus). Photo credit: USGS, courtesy USGS Southeast Ecological Science Center Photo Gallery
Northern snakehead (Channa argus). Photo credit: USGS, courtesy USGS Southeast Ecological Science Center Photo Gallery

The Northern snakehead (Channa argus) is a piscivorous fish native to eastern Asia. It is the most important snakehead cultured in China and has been purposely introduced to a number of Asian countries due to its culinary attributes. For decades this fish has been imported to the United States as a live product to meet food market and aquarium trade demand. It is believed that accidental or illegal, but purposeful introductions of this species into open waters was an artifact of this permitted live market. While it is not know when this fish was introduced into United States waters, the first documented observation of a live snakehead captured from open waters occurred in California in October of 1997. Since that time Northern snakeheads have been observed in Florida, Maryland, Virginia, North Carolina and the New England states (Courtenay et al. 2004). The presence of Northern snakeheads in the mid-Atlantic region has garnered attention given sensationalized media coverage, coupled by evidence that these populations are expanding (Odenkirk and Owens, 2007). Strategies to eradicate this invasive fish have thus far failed, and it is predicted that the Northern snakehead is likely to increase its present range (Odenkirk and Owens, 2005).

The introduction of non-native, invasive species poses the risk of introducing exotic pathogens.  During a 2006 reconnaissance a filterable agent likely of viral nature was isolated from a number of Northern snakehead in Virgina waters of the Chesapeake Bay Watershed. Classical biological methods and molecular approaches are in progress to identify the putative viral isolate. It is unknown if this agent causes disease in Northern snakehead or poses a threat to endemic species. Likewise it is unclear if the isolates ‘hitchhiked’ into the US water or if the snakeheads became infected post introduction. Active research includes the definitive identification of this isolate, and epidemiological studies to determine the geographical range.

Related Publications:

  • Courtenay, W. R. Jr., and J. D. Williams. 2004. Snakeheads (Pisces, Channidae) - A biological synopsis and risk assessment. U.S. Geological Survey Circular 1251.
  • Odenkirk, J., and S. Owens. 2005. Northern snakeheads in the tidal Potomac River system. Transactions of the American Fisheries Society 134:1605–1609.
  • Odenkirk, J., and S. Owens. 2007. Expansion of a Northern Snakehead Population in the Potomac River System. Transactions of the American Fisheries Society 136:1633–1639

For more information contact Luke R. Iwanowicz or Christine Densmore, Leetown Science Center, Fish Health Branch.

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Exploration of the Host Response to Iridovirus Exposure: Identification and Temporal Expression of Immunoregulatory Genes in Scaphirhynchus spp.
A TEM image of pallid sturgeon iridovirus (PSIV); Photo credit: Linda Beck, Bozeman Fish Technology Center, U.S. Fish and Wildlife Service
A TEM image of pallid sturgeon iridovirus (PSIV); Photo credit: Linda Beck, Bozeman Fish Technology Center, U.S. Fish and Wildlife Service
Juvenile pallid sturgeon. Photo credit: Linda Beck, Bozeman Fish Technology Center, U.S. Fish and Wildlife Service
Juvenile pallid sturgeon. Photo credit: Linda Beck, Bozeman Fish Technology Center, U.S. Fish and Wildlife Service

The pallid sturgeon was added to the Endangered Species List in 1990. Currently, captive propagation of this species is utilized as a management tool to bolster natural populations. However, such artificial culture conditions introduce generalized stressors and are often conducive to the unintended transmission of microbial pathogens. During recent years an iridovirus has been isolated from dead and moribund pallid and shovelnose sturgeon (Scaphirhynchus platyorynchus). The latter species is closely related to the pallid, and is often used as surrogate species to optimize culture conditions for captive breeding programs. We have recently developed and EST database from infected S. platyorynchus. This gene database and additional transcriptome data yielded by a massively parallel sequencing project in progress at the Leetown Science Center will be used to identify genes associated with the immune response to this virus. Quantitative PCR platforms will be utilized to assess the temporal regulation of immune related genes following virus challenge. This work is an active collaboration with the Dr. Ron Hedrick and ongoing Technical Assistance to the US Fish and Wildlife Service. Data yielded from this work should provide insight into the immune-virus response and guide actions that may ameliorate the effects of future outbreaks, or lead to prophylactic best management practices.

For more information contact Luke R. Iwanowicz, Leetown Science Center, Fish Health Branch.

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Zoonotic Fish Disease and Adaptive Fishery Management: Considerations for Striped Bass from the Chesapeake Bay
Mycobacteriosis lesions in striped bass. Photo courtesy of the Maryland Department of Natural Resources
Mycobacteriosis lesions in striped bass. Photo courtesy of the Maryland Department of Natural Resources - www.dnr.maryland.gov
Cumulative number of cutaneous mycobacteriosis cases received by month in Maryland and Virginia counties within the Chesapeake Bay watershed (2000-2005)
Cumulative number of cutaneous mycobacteriosis cases received by month in Maryland and Virginia counties within the Chesapeake Bay watershed (2000-2005). Larger view

Mycobacteriosis is a widespread, chronic disease of estuarine fishes. Recent studies by scientists at the National Fish Health Research Laboratory, Leetown, West Virginia and the Virginia Institute of Marine Science, Gloucester, have shown infection rates in striped bass (Morone saxatilis) of up to nearly 62% in certain Virginia tributaries to Chesapeake Bay. Of the several mycobacterial species known to infect striped bass, several are known to be zoonotic including M. marinum and M. fortuitum.  To investigate this potential relationship further we worked with public health officials to examine the incidence and prevalence of mycobacterial infections in striped bass and contrast these with human epidemiological data on the occurrence of cutaneous mycobacteriosis in the Bay’s human population. Using data from 1995–2005, the Commonwealth of Virginia (VA) and State of Maryland (MD) collectively demonstrated 275 cases of non-tuberculosis mycobacteria (NTM) infections by M. marinum in the human population within the Bay watershed. The data indicates that most of the persons infected were males (67%-VA; 67%-MD) between the ages of 40 and 70 (79%-VA; 62%-MD) and that most infections occurred on fingers and hands (43%-VA 63%-MD). During the same 10-year period, only four cases of NTM infection were recorded in 11 non-Bay counties from both states combined. During this same period significant increases in natural mortality among the Maryland Chesapeake Bay spring spawning stock of striped bass were noted where the instantaneous natural mortality coefficient ranged from 0.38 to 0.47. The cause(s) of this increased natural mortality are unknown. However, managers observed that these increases in mortality were concurrent with increases in prevalence and occurrence of mycobacteriosis in striped bass populations. It is not known whether or not the two conditions are related. Knowledge of fish disease processes, fish disease defense mechanisms, and ecology is important to the development of fishery management strategies. This is especially true in large, complex ecosystems such as the Chesapeake Bay where epizootic or chronic disease affect fish at the population level. While cause-and-effect relationships cannot be clearly demonstrated between the epizootic of mycobacteriosis in striped bass and these elevated incidences of NTM cutaneous infections in the human population of the Bay counties, the weight-of-evidence suggests reason for concern.  To achieve management objectives, managers should consider adaptive management techniques that incorporate aquatic animal health concerns whenever disease is implicated as a factor.

Related Publications:

Panek, F.M. and T. Bobo. 2006. Zoonotic fish disease and adaptive fishery management: Considerations from striped bass (Morone saxatilis) from the Chesapeake Bay. Proceedings of the Southeast Association of Fish and Wildlife Agencies 60: 140-144. (online proceedings, PDF, 527 KB)

Ottinger, C.and J. Jacobs., editors. 2006. USGS/NOAA Workshop on Striped Bass, 7–10 May 2006, Annapolis, Maryland. USGS, Scientific Investigations Report 2006–5214, Reston, Virginia. (online report, PDF, 824 KB)

Rhodes, M.W., H. Kator, I. Kaattari, D. Gauthier, W. Vogelbein, and C.A. Ottinger. 2004. Isolation and characterization of mycobacteria from striped bass Morone saxatilis from the Chesapeake Bay. Diseases of Aquatic Organisms 61: 41–51. (online article)

For more information contact Frank M. Panek, Leetown Science Center, Fish Health Branch.

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Q-PCR Detection of Bacterial Sources of Thiaminase I, a Potential Cause of Thiamine Deficiency and Early Mortality Syndrome in Great Lakes Salmonines
Yellow color shows thiamine degradation on an agar plate of P. thiaminolyticus strain 8120. Photo credit: Catherine A. Richter, Columbia Environmental Research Center.
Yellow color shows thiamine degradation on an agar plate of P. thiaminolyticus strain 8120.  Photo credit: Catherine A. Richter, Columbia Environmental Research Center
Image Gallery

Reproductive success of salmonines, including lake trout, in the Great Lakes has been limited by early mortality syndrome (EMS) due to thiamine (vitamin B1) deficiency in eggs.  The Gram-positive bacterium Paenibacillus thiaminolyticus produces an enzyme, thiaminase I, which degrades thiamine.  While thiamine deficiency may have multiple causes, P. thiaminolyticus is one potential cause of thiamine deficiency leading to EMS in Great Lakes salmonines.  Diets of alewife or isolated strains of P. thiaminolyticus mixed in a semipurified diet and fed to lake trout have been shown to produce EMS in fry.  Furthermore, P. thiaminolyticus has been isolated from viscera of alewife collected in Lake Michigan.  In order to aid studies of the sources of P. thiaminolyticus and thiaminase I, we have developed and characterized quantitative PCR assays for the thiaminase I gene and the 16S rRNA gene of P. thiaminolyticus.  These Q-PCR assays are being applied to identify sources of bacterial thiaminase I in Great Lakes food webs and will be of use in defining the relative importance of this cause of thiamine deficiency and in evaluating the effectiveness of management strategies for prevention of EMS in Great Lakes salmonines.

For more information, contact Catherine A. Richter, Columbia Environmental Research Center.

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Quarantine of Aeromonas salmonicida-Harboring Ebonyshell Mussels (Fusconaia ebena) Prevents Transmission of the Pathogen to Brook Trout (Salvelinus fontinalis)
Recovering bacteria from an ebonyshell Fusconaia ebena. The shells are cleaned and disinfected. Photo credit: Clifford E. Starliper, USGS
Recovering bacteria from an ebonyshell Fusconaia ebena. The shells are cleaned and disinfected. Photo credit: Clifford E. Starliper, USGS
A laboratory test to identify the bacteria from the mussels. Aeromonas salmonicida bacterial colonies shown on a differential medium (CBB). Photo credit: Clifford E. Starliper, USGS
A laboratory test to identify the bacteria from the mussels. Aeromonas salmonicida bacterial colonies shown on a differential medium (CBB). Photo credit: Clifford E. Starliper, USGS

Furunculosis, caused by the bacterium  Aeromonas salmonicida, was artificially induced in brook trout (Salvelinus fontinalis) in an experimental tank. Ebonyshells Fusconaia ebena were placed with these fish to acquire the pathogen through siphoning. After 2 weeks of cohabitation, 10 of the mussels were assayed by bacterial culture and all were found to be positive for A. salmonicida. The mean cell count from soft tissue homogenates was 1.84 ×10ˆ5 cfu/g, which comprised an average 14.41 % of the total bacteria isolated from tissues. From the fluids, a mean of 2.84 × 10ˆ5 A. salmonicida cfu/mL was isolated, which comprised an average of 17.29 % of the total bacterial flora from fluids. The mussels were then removed from the cohabitation tank and distributed equally among five previously disinfected tanks. The F. ebena in each tank were allowed to depurate A. salmonicida for various durations: 1, 5, 10, 15 or 30 days. After each group had depurated for their assigned time, ten were assayed for bacteria, tank water was tested and 20 pathogen-free bioindicator brook trout were added to cohabit with the remaining mussels. Depuration was considered successful if A. salmonicida was not isolated from tank water or the mussels and there was no infection or mortality to bioindicator fish. After 1 day of depuration, A. salmonicida was not isolated from the soft tissues; however, it was isolated from one of the paired fluids (10% prevalence). The tank water was positive and the bioindicator fish became infected and died. From the 5-day depuration group, A. salmonicida was not isolated from soft tissues, but was isolated from three fluids (30 %; mean = 1.56 × 10ˆ2 cfu/mL). Tank water from the 5-day group was negative and there was no mortality among the bioindicator fish, however, A. salmonicida was isolated from 2 of 20 of the fish at the end of the 14-day observation period. One F. ebena fluid sample was positive for A. salmonicida from the 10-day depuration group, but none of the soft tissue homogenates. The pathogen was not isolated from 10-day tank water, but there was a 30 % cumulative mortality to the bioindicator fish. Aeromonas salmonicida was not isolated from any of the soft tissue homogenates, fluids or tank water from the 15 day or 30 day depuration groups and the bioindicator fish remained pathogen and disease free. Results of this study showed that the F. ebena were harboring a high A. salmonicida cell load, but after 15 days of depuration, this bacterium the mussels did not serve as pathogen vectors.

Publication:

Starliper, C.E. 2005. Quarantine of Aeromonas salmonicida-harboring ebonyshell mussels (Fusconaia ebena) prevents transmission of the pathogen to brook trout (Salvelinus fontinalis). Journal of Shellfish Research. 24(2):573-578.

For more information contact Clifford E. Starliper, Leetown Science Center.

See also Fish and Wildlife Disease: Mollusks >>

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Recovery of a Fish Pathogenic Bacterium, Aeromonas salmonicida, from Ebonyshell Mussels Fusconaia ebena using Non-Destructive Sample Collection Procedures
Collecting hemolymph from the adductor muscle of a mussel specimen using a needle and syringe. Photo credit: USGS
Collecting hemolymph from the adductor muscle of a mussel specimen using a needle and syringe. Photo credit: Clifford E. Starliper, USGS
Two students using a ruler-board to measure and collect data from mussel specimens. The data collected include length, weight, width, depth, area inside valves, weight of soft tissues, etc. Photo credit: USGS
Two students using a ruler-board to measure and collect data from mussel specimens. The data collected include length, weight, width, depth, area inside valves, weight of soft tissues, etc. Photo credit: Clifford E. Starliper, USGS

Refugia are increasingly being employed to maintain and propagate imperiled freshwater mussels for future population augmentations. Success for this endeavor is dependent on good husbandry, including a holistic program of resource health management. A significant aspect to optimal health is the prevention or control of infectious diseases. Describing and monitoring pathogens and diseases in mussels involves examination of tissues or samples collected from an appropriate number of individuals that satisfies a certain confidence level for expected prevalences of infections. In the present study, ebonyshell mussels Fusconaia ebena were infected with a fish pathogenic bacterium, Aeromonas salmonicida, through their cohabitation with diseased brook trout Salvelinus fontinalis. At a 100 % prevalence of infection, the F. ebena were moved to clean tanks that were supplied with pathogen-free water, which initiated their depuration of A. salmonicida. Three samples (non-destructive fluid, mantle, hemolymph) collected using non-destructive procedures were compared to fluids and soft tissue homogenates collected after sacrificing the mussels for recovery of the bacterium. The results showed that the non-destructive sample collections, particularly fluid, provide a comparable alternative to sacrificing mussels to determine pathogen status.

Publication:

Starliper, C. E. 2008. Recovery of a fish pathogenic bacterium, Aeromonas salmonicida, from ebonyshell mussels Fusconaia ebena using non-destructive sample collection procedures. Journal of Shellfish Research. 27(4): 775-782.

For more information contact Clifford E. Starliper, Leetown Science Center.

See also Fish and Wildlife Disease: Mollusks >>

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Pathogens Associated with Trout Populations and the Relationships to Fish Stocking Practices in National Parks
Brook trout netted. Photo Credit: Shenandoah National Park
Brook trout netted. Photo Credit: Shenandoah National Park

Threats to native fish populations from stocking non-native species and their associated disease concerns are important nat­ural resource management issues in the U.S. National Parks. Re­strictive fish stocking policies in National Parks were developed as early as 1936 in order to preserve native fish assemblages and genetic diversity. These policies were based largely on the assumptions that fish stocking practices could affect native biological communities and populations.  Despite efforts to understand the effects of non-native or exotic fish introductions, park managers have limited information regarding the effects of these introductions on native fish communities.  In this study we investigated the occurrence and prevalence of selected fish pathogens in wild trout populations in Shenandoah National Park.  Specifically, we examined the occurrence of a suite of pathogens of national and regional significance collected as part of the U.S. Fish and Wildlife Service’s (USFWS) National Wild Fish Health Survey (NWFHS). We correlated these findings with known stream stocking histories to assess the potential linkages of past stocking practices and the occurrence of pathogens. Fish were collected from three categories of streams supporting wild trout populations: streams with no known stock­ing history within the park, streams historically stocked within the park, and streams within the park that were historically stocked and are presently stocked downstream of the park boundary. Our findings were based on the collection and analysis of over 1,400 brook, brown, and rainbow collected from 29 steams in Shenandoah National Park.  Based on our findings, pathogens and fish diseases are not a significant trout management issue in the park. Of the ten pathogens of national and regional importance tested during this investigation we only documented the occurrence of Renibacterium salmoninarum, Yersinia ruckeri, and infectious pancreatic necrosis virus (IPNv). Nevertheless, we do have evidence to suggest an increased occur­rence and prevalence of pathogens in trout populations from streams that were either historically stocked within the park or are pres­ently stocked to supplement recreational fisheries downstream of the park boundary. Based on our findings, we recommend that park managers carefully weigh the advantages and disadvantages of fish stocking for either recre­ational or restoration purposes within parks. Any fish stockings should be accompanied by fish health inspections to ensure that hatchery fish or wild fish translo­cated for restoration purposes are pathogen free.

Related Publications:

Panek, F.M., J. Atkinson and J. Coll. 2008. Pathogens associated with trout populations in Shenandoah National Park and the relationships to fish stocking practices. Proceedings of the Southeast Association of Fish and Wildlife Agencies 62: 131-135. (online proceedings, PDF, 143 KB)

Panek, F.M. 1997. Threats, risks and promises: Challenges for trout manage­ment in the twenty-first century. Fisheries 22(6): 24–26. (online article)

Wright, G.R. 1992. Wildlife Research and Management in the National Parks. University of Illinois Press, Chicago.

For more information contact Frank M. Panek, Leetown Science Center, Fish Health Branch.

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Viral Hemorrhagic Septicemia Virus in the Great Lakes
Great Lakes. Photo credit: Jeff Schmaltz/NASA
Great Lakes. Photo credit: Jeff Schmaltz/NASA

Viral hemorrhagic septicemia (VHS) is considered to be the most important viral disease of finfish worldwide and is listed as reportable by many nations and international organizations. Prior to 1988, VHS was not known to occur outside of continental Europe where it affected rainbow trout aquaculture. Subsequently, a North American strain of the causative rhabdovirus, VHSV, was found to be endemic among marine fish on the Pacific coast of North America where it was shown to be highly pathogenic for marine species, especially herring. Surveys in other regions of the world have revealed that VHSV is also endemic among marine species in the North Atlantic, the Baltic Sea, the North Sea and Japan. Beginning in 2005, reports from the Great Lakes region indicated that wild fish had experienced disease or, in some cases, very large die-offs from VHS. The USGS Western Fisheries Research Center (WFRC) has conducted research on VHSV for more than 20 years providing technical assistance and information to fisheries managers at state, federal, tribal and private sector entities as well as to the news media. Research at the WFRC has developed novel tools for the detection and identification of VHSV and used molecular epidemiology to show that the strain of VHSV affecting fish in the Great Lakes Basin is a new genotype of the virus, now identified as Genotype IVb. The type IVb isolate found in the Great Lakes region is the only strain of VHSV that has been linked to large natural mortalities among freshwater species. As of spring 2008, VHSV has been isolated from more than 25 species of fish, some of which suffered substantial mortality, in Lake Michigan, Lake Huron, Lake St. Clair, Lake Erie, Lake Ontario and the St. Lawrence River as well as inland lakes in Wisconsin, Michigan and Ohio.

Links to VHSV Fact Sheets:

For further information contact James R. Winton, Western Fisheries Research Center.

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Warming Climate Can Affect Fish Health
Heart of adult Chinook salmon showing signs of Ichthyophonus infection. Photo credit: R. Kocan, University of Washington
Figure 1. Heart of adult Chinook salmon showing multiple, small, white, focal lesions typical of Ichthyophonus infections in salmonids. These cardiac lesions are believed to be the cause of reduced swimming stamina among infected fish. Photo credit: R. Kocan, University of Washington
Effect of temperature on the swimming performance (time-to-fatigue) of Ichthyophonus-infected and uninfected rainbow trout.
Figure 2. Effect of temperature on the swimming performance (time-to-fatigue) of Ichthyophonus-infected and uninfected rainbow trout. The increase in stamina with increased temperature was significant (AOVA; P = 0.007) for controls, but not for infected fish (P = 0.26). Bars = 1 SD of the mean, * = significant difference in performance between infected and control fish (paired t-Test). Larger view

Ichthyophonus is a fungal-like protist that has caused disease in several species of marine fish in the Pacific and Atlantic Oceans including several waves of population-scale losses in Atlantic herring. More recently, reports from subsistence fishermen and tribal elders indicate the emergence of Ichthyophonus infections in adult Chinook salmon returning to the Yukon River in Alaska that are associated with adverse flesh quality and possible pre-spawning losses. A field study examined Chinook at multiple sites within the Yukon system to assess prevalence of Ichthyophonus infection and disease. Clinical signs of disease were minimal when fish entered the river, but increased significantly when fish reached the middle river. Among fish from the end of the run, the parasite was disseminated and clinical disease was apparent in multiple organs, especially the heart (Figure 1); however, female spawn-outs had lower levels of Ichthyophonus suggesting the most severely diseased fish had died before spawning. Elevated river temperatures in recent decades were postulated to be an important cause of the emergence and increased severity of the disease. To understand the role of temperature on the disease process infected and control groups of rainbow trout were held at 10, 15 and 20°C for 28 days to monitor mortality and disease progression. Infected fish demonstrated more rapid onset of disease, higher parasite load and a faster death rate at higher temperature. In a second experiment to determine the role of temperature on the swimming stamina of Ichthyophonus-infected fish, infected trout were reared at 15°C for 16 weeks before being subjected to forced swimming at 10, 15 and 20°C. Stamina was significantly impaired in infected fish as temperature increased (Figure 2). This study highlights the role of environmental stressors, such as climate change, on the ecology of fish diseases as well as the impact of these diseases on fitness traits important to the survival of natural populations.

For further information contact James R. Winton, Western Fisheries Research Center.

See also Climate Change: Disease Impacts >>

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