Immune Function of Wild Smallmouth Bass Collected from Sites within the Chesapeake Bay Watershed, 2016-2021

Adult and young of the year smallmouth bass from the Chesapeake Bay watershed have faced health issues (mortality events, disease by a variety of pathogens, endocrine disruption in male fish, evidence of oxidative damage to tissues, and signs of exposure to chemical contaminants) at multiple sites within the Susquehanna and Potomac River basins. Functional immune assays were added to long-term comprehensive monitoring assessments to determine if immunosuppression was playing a role in observed disease and mortalities because no one single or consistent cause could be identified. The functional immune assays measured bactericidal activity, respiratory burst activity, and lymphocyte mitogenesis using leukocytes isolated from anterior kidney tissue. From 2016-2021, a total of 740 smallmouth bass were sampled among eight (8) sites. Twenty adults were sampled from each site in spring (pre-spawn; April – May) and fall (recrudescence; October – November) at different points in the study. Ancillary data, including biometrics of the fish and parasite/macrophage aggregate counts in multiple tissue types, were collected in conjunction with the immune data. The functional immune assays serve as part of an integrated assessment to determine environmental stressors and infectious agents that may modulate the immune response in wild smallmouth bass, ultimately making them more susceptible to disease and death. Therefore, it is important to consider the functional immune data alongside other aspects of host and environmental health.