28th ANNUAL EASTERN FISH HEALTH WORKSHOP April 21-25, 2003 Mycobacteriosis In Striped Bass: Comparative Analysis In Four Chesapeake Bay Tributaries Christine L. Densmore United States Geological Survey, Leetown Science Center, National Fish Health Research Laboratory, 11700 Leetown Road, Kearneysville, WV  25430 There remain many fundamental questions pertaining to the etiology and pathogenesis of mycobacteriosis among striped bass (Morone saxatilis) populations from the Chesapeake Bay and its tributaries.  While many researchers from different organizations have investigated various aspects of this problem over the past few years, differences in methodologies have largely precluded direct comparisons of results.  In 2002, researchers from federal and state agencies as well as academic institutions (USGS, USFWS, NOAA, Maryland DNR, Virginia Institute of Marine Science and the University of Maryland) began development of standardized methods for field and laboratory techniques to be utilized in a joint study.  Specifically, the multi-year study initiated in fall 2002 characterized mycobacteriosis among striped bass at 4 sample sites from Chesapeake Bay tributaries in both Maryland (Potomac and Nanticoke Rivers) and Virginia (York and Rappahannock Rivers).  Within a two-week period, 50 adult striped bass were harvested from pound nets at each sample site and processed on site in the field via necropsy and tissue collection. Length and weight were determined, blood samples were collected, and fish were examined for presence of gross external and internal lesions. Tissue samples were returned to the laboratory for microbial culture and histopathological analysis.  Aseptically collected samples of spleen were used for quantitative cultures with both a nonselective media and media selective for Mycobacterium sp.  Samples of spleen, liver, hematopoietic kidney, gill, and skin collected in fixative were processed and examined by light microscopy.   Compiled results for each fish sampled included descriptions of presence and load of Mycobacterium sp. as well as other bacteria cultured from splenic tissue.  Condition factor, gross and histological lesions, and plasma cortisol levels were also assessed.  Results will subsequently be compared geographically (tributary to tributary) and chronologically (year to year).  Through these standardized field and laboratory methods, our goal was to address a number of questions related to the frequency, specific etiology, clinical presentation, and geographic distribution of mycobacteriosis and its causative agents among the striped bass population in the Chesapeake Bay watershed. Return to 28th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page