Characterizing the Adaptive Potential of Chinook Salmon to Resist Disease

Mass mortality events due to infectious disease agents in wild fish populations are troubling, but it is the long-term, population-level consequences which may be of more significance. Basic evolutionary theory predicts that populations with sufficient genetic variation will adapt in response to pathogen pressure. Chinook salmon were introduced into Lake Michigan in the late 1960s from a Puget Sound population (Washington State). In the late 1980s, collapse of the forage base in Lake Michigan was thought to contribute to die-offs of Chinook salmon due to Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD). Evidence from our laboratory demonstrates that Chinook salmon from Lake MI, Wisconsin have greater survival following R. salmoninarum challenge relative to several Pacific Northwest populations, including its progenitor population. Our present study seeks to characterize (1) the genetic basis for survival following Renibacterium salmoninarum infection in a Lake MI population of Chinook salmon and (2) to exploit the genetic relationships within the study to identify prognostic biomarkers for BKD. Biomarkers are assays that measure a response at a molecular, cellular or tissue level but have prognostic capabilities at higher levels of biological complexity (e.g. organism, population or ecosystem). Some current diagnostic assays are capable of quantitatively measuring R. salmoninarum levels, but there are no assays that reliably provide disease prognosis. Biomarkers that are closely associated with BKD-related host responses, pathophysiology or pathology may have improved prognostic capabilities for disease status. Previous studies have identified several candidate biomarkers for BKD, including gene and serum assays for inducible nitrate. In the present study, we are evaluating whether these candidate biomarkers are significantly associated with pathological or pathophysiological changes and/or are predictive of mortality.