Mortality of centrarchid fishes in the Potomac drainage: Survey results and overview of potential contributing factors

Journal of Aquatic Animal Health
By: , and 



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.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Mortality of centrarchid fishes in the Potomac drainage: Survey results and overview of potential contributing factors
Series title Journal of Aquatic Animal Health
DOI 10.1577/H10-002.1
Volume 22
Issue 3
Year Published 2010
Language English
Publisher Francis & Taylor
Publisher location London, UK
Contributing office(s) Leetown Science Center, Toxic Substances Hydrology Program
Description 29 p.
First page 190
Last page 218
Country United States
State Maryland, Pennsylvania, Virginia, West Virginia
Other Geospatial Potomac River
Additional Online Files (Y/N) N
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