Abstract

In recent years, concerns about the health and population status of striped bass (Morone saxatilis) in the Chesapeake Bay and its tributaries have been widespread among the popular and scientific communities. Research efforts to address this issue have revealed a significant level of mycobacteriosis among striped bass from the Chesapeake Bay and its watershed. In some regions of the Bay waters, the prevalence of infection with Mycobacterium sp. among striped bass has been reported to reach approximately 70%. As these fish represent an important commercial and recreational resource for the mid-Atlantic region, population-level impacts and increased numbers of lesioned, disfigured fish would likely have considerable economic and ecological impacts.

In 2002, a cooperative research project to examine this problem in detail was initiated by scientists at a number of institutions including federal and state agencies (USGS, USFWS, Maryland DNR) as well as academic institutions (Virginia Institute of Marine Science, University of Maryland). The objectives of this multi-year study are to gain a better understanding of the precise etiology, pathogenesis, prevalence, and geographic distribution of mycobacteriosis among Chesapeake Bay striped bass in both Maryland and Virginia waters through the use of standardized methods. In fall of 2002 and 2003, wild striped bass were sampled from pound nets (n= 50 fish per site each year) in four tributaries of the Chesapeake Bay: the Potomac and Nanticoke rivers in Maryland, and the York and Rappahannock rivers in Virginia. Necropsies were conducted on all sampled fish, and tissue specimens collected for microbial analysis and histopathological evaluations. Prevalence and degree of Mycobacterium sp. infection is determined through microbial analysis of the aseptically harvested spleen samples, including both quantification and speciation. Mycobacteriosis is also assessed through the presence of gross and histologic lesions consistent with this disease. Based on the data collected during the 2002 sampling, there are differences apparent in both prevalence of infection and clinical impacts of mycobacteriosis among the four Chesapeake Bay tributaries. Data analysis for the 2003 sample collection is underway.

In order to ascertain the impacts of mycobacteriosis beyond the Chesapeake Bay and its tributaries, similar assessments are being conducted or are planned for other sites in this region. A similar cooperative effort involving investigators from USGS, USFWS, and Delaware DNR is underway to evaluate the prevalence and presentation of mycobacteriosis among striped bass from the Delaware Bay.