28th ANNUAL EASTERN FISH HEALTH WORKSHOP April 21-25, 2003 Concurrent Infection Of Hybrid Striped Bass (Morone chrysops X Morone saxatilis) With Three Bacterial Pathogens:  A Case Report Paul R. Bowser1, Gregory A. Wooster1, Chun-Yao Chen1 and Rachel S. Mo2 1Aquatic Animal Health Program, Department of Microbiology and Immunology; 2Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853-6401 In this report we document a concurrent infection of hybrid striped bass (Morone chrysops X Morone saxatilis) with three bacterial pathogens, Aeromonas salmonicida, Listonella (Vibrio) anguillarum, and Mycobacterium sp.  We present this case due to its unusual multiple etiologies.  A group of approximately 120 hybrid striped bass were obtained from a commercial facility and brought to our Aquatic Animal Health Program facilities for use in an ongoing research effort.  The fish were 450-500 g each and had been cultured in a recirculating aquaculture system (RAS) at 26oC at salinity of 6 ppt.  The fish were in transit for approximately 8 hours and were observed to be in poor general body condition upon arrival.  Approximately 20% of the fish had hemorrhagic skin lesions while approximately 5% of the fish had exophthalmia.  During the 7-day acclimation period a steadily increasing daily mortality was observed. Fifteen fish that had demonstrated the external hemorrhagic lesions common to the disease syndrome in question were selected for diagnostic processing.  The fish were euthanized by an overdose (> 500 mg/L) of methane tricainesulfonate (MS-222, Sigma, St. Louis, Missouri, USA) prior to processing.  Microscopic examination of skin scrapings (normal and abnormal areas) and gill biopsies did not reveal any external pathogens.  Bacterial cultures were taken from the posterior region of the kidneys and plated onto brain heart infusion agar and blood agar and were incubated at 25oC for 5 days.  Cultures were then submitted to the New York State Veterinary Diagnostic Laboratory for identification by fatty acid analysis.  Aeromonas salmonicida and Listonella (Vibrio) anguillarum were identified.  Histological evaluation of fixed tissues revealed multiple granulomas in liver, kidney and spleen as well as focal areas of necrosis in the same organs.  Acid-fast organisms, most likely Mycobacterium sp. were associated with the granulomas, while Gram negative organisms were associated with the necrotic foci.  This case highlights challenges faced by individuals responsible for fish health management in such culture systems.  Return to 28th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page