IMMUNE FUNCTION IN SMALLMOUTH BASS (MICROPTERUS DOLOMIEU) FROM THE CHESAPEAKE BAY WATERSHED
Cheyenne Smith, National Fish Health Research Laboratory
Cheyenne Smith1,2, Chris Ottinger1, Vicki Blazer1, and Luke Iwanowicz1
1. U.S. Geological Survey, National Fish Health Research Laboratory, Kearneysville, WV
2. Department of Environmental Biology, Hood College Graduate School, Frederick, MD
The Potomac and Susquehanna Rivers, both tributaries to the Chesapeake Bay, are sites that have experienced major fish kills beginning in 2002 for adults (Potomac) and 2005 for young of the year (Susquehanna). Fish health investigations indicated smallmouth bass from both river basins have a variety of bacterial infections, heavy parasite loads, and sometimes viral and fungal infections. Because no single or consistent cause can be identified, we believe the fish are immunosuppressed due to contaminants and other stressors and thus susceptible to many opportunistic pathogens. Fish were collected from four sites with varying levels of agricultural land use and wastewater input. Anterior kidney tissue was removed from 20 adult smallmouth bass at each site. Samples were collected across three sampling seasons beginning in spring 2016 and continuing to spring 2017. Bactericidal killing ability, respiratory burst activity, and lymphocyte mitogenesis were used as measures of immune function. We modified classical diagnostics for these assays, which involves spectrophotometric analysis, to image-based flow cytometry. This allowed collection of single cell reads and determination of responses for individual cells classified based on width, cell surface markers and nuclear morphology. For mitogenesis, the main differences found were between our reference site (high forested, low agriculture) and high agricultural site for cells that were 10 μm and 12 μm in width. Oxidative stress appeared to play a role in these differences. Additional analyses are still underway and the immune function results are being integrated with water contaminant concentrations measured monthly, tissue histopathology and plasma analyses.