Physiological Effects of Sublethal Hypoxia on Atlantic Croaker in Chesapeake Bay

Low dissolved oxygen (DO) is an increasingly common problem during the summer months in the Chesapeake Bay. Both natural and anthropogenic factors combine to increase the intensity and extent of hypoxic events and thus further stress aquatic organisms such as Atlantic croaker. While the lethal effects of hypoxia are easily observed the sublethal but physiologically relevant effects are more obscure and complicated by other endogenous and exogenous factors. In this study, the physiological responses of croaker to sublethal hypoxia were evaluated under laboratory conditions in order to better understand how organisms react to changes and stressors in their environment. Twenty wild-caught fish each were held in normoxic (6 mg/L) and hypoxic (2 mg/L) tanks. Five fish from each tank were sacrificed at time zero and again at 1, 4, and 8 weeks. Blood and tissue samples were collected in order to assess overall health, reproductive, and immune functions of croaker. Results obtained from the lab study governed the assays used in the field study. Improved information on immune response and croaker hypoxia biomarkers were key results from this project