Hypercapnic Hypoxia Compromises bactericidal activity of fish phagocytic cells against opportunistic environmental pathogens

Kimberley A. Boleza, M.S.

Dept. of Microbiology and Immunology, Medical University of South Carolina

Grice Marine Laboratory, University of Charleston, Charleston, SC 29412

ABSTRACT:  Acute hypoxia can cause massive fish and shellfish mortalities. In contrast, the role that chronic sublethal hypoxia plays in aquatic animal health is less clear. This study tested whether bacterial killing activity of fish phagocytic cells is suppressed by conditions of dissolved gasses and pH that occur in blood and tissue of animals exposed to sublethal hypoxia. Anterior head kidney cells of the mummichog, Fundulus heteroclitus, were exposed in parallel to normoxic and hypoxic conditions and stimulated with zymosan or live Vibrio parahaemolyticus. Production of reactive oxygen species by the respiratory burst was measured by chemiluminescence and nitroblue tetrazolium assays, and bactericidal activity quantified by a colorimetric assay for surviving bacteria. At the levels of hypoxia tested in this study, low oxygen alone did not have a significant impact on bacterial killing activity. However, the combination of low oxygen, high carbon dioxide and low pH that characterize naturally occurring hypercapnic hypoxia did suppress bacterial killing activity mediated by the respiratory burst. These results indicate a specific mechanism by which sublethal hypercapnic hypoxia might increase susceptibility to infectious disease in aquatic populations. Water quality regulators should consider the effects of changes in dissolved gasses and pH as compounding factors when setting criteria for trace anthropogenic contaminants.

Published:  Boleza, K.A., Burnett, L.E. and Burnett, K.G.  2001.  Hypercapnic hypoxia compromises bactericidal activity of fish anterior kidney cells against opportunistic environmental pathogens.  Fish & Shellfish Immunol. 11:593-610.