Mortality of Centrarchid Fishes in the Potomac Drainage: Survey Results and Overview of Potential Contributing Factors

Skin lesions and spring mortality events of smallmouth bass Micropterus dolomieu and selected other species were first noted in the South Branch of the Potomac River in 2002. Since that year morbidity and mortality have also been observed in the Shenandoah and Monocacy rivers. Despite much research,...

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Bibliographic Details
Published in:	Journal of aquatic animal health Vol. 22; no. 3; pp. 190 - 218
Main Authors:	Blazer, V. S., Iwanowicz, L. R., Starliper, C. E., Iwanowicz, D. D., Barbash, P., Hedrick, J. D., Reeser, S. J., Mullican, J. E., Zaugg, S. D., Burkhardt, M. R., Kelble, J.
Format:	Journal Article
Language:	English
Published:	United States Taylor & Francis Group 01-09-2010
Subjects:	Aeromonas hydrophila Aeromonas salmonicida Animals Ecosystem Fish Diseases - epidemiology Fish Diseases - microbiology Fish Diseases - mortality Flavobacterium columnare Freshwater Largemouth bass virus Micropterus dolomieu Perciformes Rivers Time Factors USA, Maryland, Potomac R USA, Maryland, Monocacy R
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Summary:	Skin lesions and spring mortality events of smallmouth bass Micropterus dolomieu and selected other species were first noted in the South Branch of the Potomac River in 2002. Since that year morbidity and mortality have also been observed in the Shenandoah and Monocacy rivers. Despite much research, no single pathogen, parasite, or chemical cause for the lesions and mortality has been identified. Numerous parasites, most commonly trematode metacercariae and myxozoans; the bacterial pathogens Aeromonas hydrophila, Aeromonas salmonicida, and Flavobacterium columnare; and largemouth bass virus have all been observed. None have been consistently isolated or observed at all sites, however, nor has any consistent microscopic pathology of the lesions been observed. A variety of histological changes associated with exposure to environmental contaminants or stressors, including intersex (testicular oocytes), high numbers of macrophage aggregates, oxidative damage, gill lesions, and epidermal papillomas, were observed. The findings indicate that selected sensitive species may be stressed by multiple factors and constantly close to the threshold between a sustainable (healthy) and nonsustainable (unhealthy) condition. Fish health is often used as an indicator of aquatic ecosystem health, and these findings raise concerns about environmental degradation within the Potomac River drainage. Unfortunately, while much information has been gained from the studies conducted to date, due to the multiple state jurisdictions involved, competing interests, and other issues, there has been no coordinated approach to identifying and mitigating the stressors. This synthesis emphasizes the need for multiyear, interdisciplinary, integrative research to identify the underlying stressors and possible management actions to enhance ecosystem health.
Bibliography:	Present address: Laboratory Services Program, U.S. Environmental Protection Agency, Region 8, 16194 West 45th Drive, Golden, Colorado 80403, USA. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0899-7659 1548-8667
DOI:	10.1577/H10-002.1