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

January 1, 2010

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.

Publication Year 2010
Title Mortality of centrarchid fishes in the Potomac drainage: Survey results and overview of potential contributing factors
DOI 10.1577/H10-002.1
Authors Vicki Blazer, Luke R. Iwanowicz, Clifford E. Starliper, Steven D. Zaugg, Mark R. Burkhardt, P. Barbash, J.D. Hedrick, S.J. Reeser, J.E. Mullican, J. Kelble
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Aquatic Animal Health
Index ID 70043460
Record Source USGS Publications Warehouse
USGS Organization Leetown Science Center; Toxic Substances Hydrology Program