Assessing the Risk of Emergent and Endemic Fish Pathogens to Great Lakes Lake Sturgeon (Acipenser fulvescens) Populations

 

 1,2Amber E. Johnston, 1,2Megan A. Shavalier, 2Kim T. Scribner, 3Esteban Soto, 4Edward A. Baker, 2Douglas L. Larson, 1,2,5Thomas P. Loch 

1Michigan State University- Aquatic Animal Health Lab, 1129 Farm Lane, Rm 340G, East Lansing MI, 48824; 2Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University; 3Department of Epidemiology, School of Veterinary Medicine, University of California-Davis; 4Michigan Department of Natural Resources 5; Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University

ABSTRACT

Only one sturgeon species (e.g., lake sturgeon, Acipenser fulvescens) is indigenous to the Great Lakes (GL), where it is the largest and longest-lived fish. Unfortunately, GL lake sturgeon (LST) populations have suffered significant population declines, necessitating hatchery-based conservation. Meanwhile, sturgeon farming in other parts of North America has grown, and with it, reports of  multiple sturgeon-pathogenic microbes (e.g., Acipenserid Herpesviruses, White Sturgeon Iridovirus, etc.) that have apparently expanded in range and seem to be encroaching upon the GL basin. Regrettably, very little is known about the infectious diseases affecting GL-LST, nor whether they are impediments to ongoing conservation efforts. To address this knowledge gap, this ongoing study aims to: a) assess the health of wild and cultured GL-LST populations; b) elucidate susceptibility of GL-LST to emerging and endemic sturgeon-pathogenic microbes; and c) develop efficacious disinfection methods to prevent and control pathogen transmission under field and hatchery conditions. Over a two year period, blood and tissue biopsies have thus far been non-lethally collected from >300 adult LST inhabiting the St. Clair (Lake Erie watershed), Peshtigo (Lake Michigan watershed), and Black (Lake Huron watershed) rivers for virological, bacteriological, mycological, histopathological, molecular, and/or hematological analyses. Likewise, tissues were also collected and clinical examination performed on >500 juvenile LST reared in facilities on the Whitefish, Cedar, Black, and West Branch Ontonagon rivers. Although analyses are ongoing, a significant finding thus far has been the detection of grossly similar cutaneous lesions in adult GL-LST collected from two of the three sampled sites at a prevalence ranging from ~1%-14%. Gross and histological evaluation of these lesions revealed a resemblance to skin lesions present in other sturgeon species previously linked to acipenserid herpesviruses. Subsequent PCR analysis of skin lesion tissues, followed by sequencing of a partial stretch of the DNA polymerase gene and phylogenetic analyses, revealed the presence of an Acipenserid Herpesvirus that was most similar, yet distinct from Acipenserid Herpesvirus 1. Currently, there are no published reports of acipenserid herpesviruses within the Great Lakes Basin in general or Michigan in specific. The potential significance of these findings, as well as other ongoing aspects of this study, will be discussed.