Application of Molecular Pathology Techniques to Understand Mechanisms of Disease in Smallmouth Bass

In the Chesapeake Bay drainage, smallmouth bass Micropterus dolomieu are used as an indicator species of estrogenic contaminant exposure and have been implicated in fish kills and disease since 2005. In the Potomac River drainage, adult smallmouth bass have experienced mortality and disease and males have a high prevalence of intersex (testicular oocytes). Conversely, in the Susquehanna River drainage mortalities and disease of young-of-the-year smallmouth bass (YOY SMB) have occurred and resulted in a population shift to older and larger fish. The exact cause of these events remains unknown; however, factors such as poor water quality, contaminants, pathogens and parasites, increased temperatures, and nutrification have been assessed. In order to address this issue, the USGS Fish Health Branch, Leetown Science Center, and West Virginia Cooperative Fish and Wildlife Research Unit have ongoing assessment and monitoring projects throughout the Chesapeake Bay watershed. The use of routine histopathology has provided guidance for further research with molecular endpoints that may help explain the mechanisms involved in disease in smallmouth bass. The purpose of this dissertation research was to: 1.) Identify the prevalence of coinfections and risk factors of disease in YOY SMB; 2.) Use in situ hybridization to identify coinfections of bacteria with the myxozoan parasite Myxobolus inornatus in YOY smallmouth bass; 3.) Model liver helminths and coinfections of YOY SMB with land use at two spatial scales; 4.) Develop laser capture microdissection methods for nucleic acid extractions which could be used with smallmouth bass tissues; and 5.) Utilize Next-Generation Sequencing to develop a partial testes transcriptome to identify molecular markers that may help explain intersex development in male smallmouth bass