Effects Of Hypercapnic Hypoxia On The Bactericidal Activity Of Hemocytes From The Penaeid Shrimp Litopenaeus vannamei       Austin S. Dantzler, Karen G. Burnett, and Louis E. Burnett   Graduate Program in Marine Biology and The Grice Marine Laboratory, University of Charleston, South Carolina         The high densities of shrimp found in aquaculture ponds often cause dissolved oxygen levels to fall below 30% air saturation.  Low oxygen is usually accompanied by increased carbon dioxide and low pH.  Previous studies from our lab demonstrated that these conditions of hypercapnic hypoxia decreased the resistance of aquacultured shrimp Litopenaeus vannamei to infection with the opportunistic bacterial pathogen Vibrio parahaemolyticus.  To understand more about the mechanisms that might underlie this effect of dissolved gasses and pH on the susceptibility to infectious disease, the current study focused on the changes in in vitro bactericidal activity of hemocytes from the white shrimp L. vannamei under conditions of hypercapnic hypoxia.  Antibacterial activity was measured using a tetrazolium dye-based bacterial killing assay.  Hemocyte preparations exhibited two patterns of killing activity.  The first pattern was characterized by the ability of lysed hemocytes to support bacterial growth.  Hypercapnic hypoxia suppressed the antibacterial activity of these hemocyte preparations.  The second pattern was characterized by the ability of lysed hemocytes to inhibit bacterial growth.  Hypercapnic hypoxia did not impact the antibacterial killing activity of these hemocyte preparations.  (USDA CSREES 99-35204-8555).