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

Abstract

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.

Transgenic Zebrafish Reveal Tissue-Specific Differences in Estrogen Signaling in Response to Environmental Water Samples

“…To concentrate estrogens over time, passive sampling devices [Polar Organic Chemical Integrative Sampler (POCIS), fabricated at the U.S. Geological Survey (USGS) Columbia Environmental Research Center (Columbia, MO) as described by Alvarez et al (2004)] were deployed in rivers and streams at 19 locations in the Shenandoah watershed and the Allegheny, Delaware, and Susquehanna Rivers in Virginia and Pennsylvania in April 2010 and remained in place for 31–45 days (see Supplemental Material, Table S1). The Shenandoah and Susquehanna sites are part of an ongoing monitoring and research program to determine the factors involved in fish lesions and mortalities and to assess signs of reproductive endocrine disruption (testicular oocytes and plasma vitellogenin in male bass) observed in these watersheds (Blazer et al 2010; Reif et al 2012). The Allegheny and Delaware sites were used as comparisons for the Susquehanna sites in the Pennsylvania emerging contaminants project (Reif et al 2012).…”

Reproductive health indicators of fishes from Pennsylvania watersheds: association with chemicals of emerging concern

“…Since then, mortalities have also occurred in the Shenandoah and the Monocacy Rivers, both tributaries of the Potomac River, and moderate to high prevalence of TO has been documented at these sites as well (Blazer et al 2007; Iwanowicz et al 2009; Blazer et al 2010). Mortalities in the Potomac drainage have involved mature adult fishes and occurred in the spring.…”

“…The location, extent, and severity of these mortalities have varied annually, and no single pathogen or water quality parameter has been identified as the cause. Rather, the numerous bacterial pathogens isolated and parasites observed suggest general immunosuppression, most likely resulting from exposure to numerous environmental stressors (Blazer et al 2010). The co-occurrence of skin lesions and excessive mortality and signs of exposure to EDC (intersex and vitellogenin in male fish) suggest that chemicals associated with feminization of male fishes might also be associated with reduced disease resistance.…”

Reproductive endocrine disruption in smallmouth bass (Micropterus dolomieu) in the Potomac River basin: spatial and temporal comparisons of biological effects

“…Consequently, biological impairment is often reflected by physiological and pathological indicators even when no impairments are predicted based on individual chemical indicators (Yoder and Rankin 1998; Adams 2002). Recurring fish mortalities during which a variety of microbial pathogens and parasites are observed have occurred in the Potomac drainage (Blazer et al 2010). The subsequent observation of a high prevalence of intersex, specifically testicular oocytes (TO) in smallmouth bass Micropterus dolomieu in these same areas, has raised concerns among natural resource agencies, as well as the general public, regarding the health of the associated watershed.…”