1. Department of Pathophysiology, Forensic Veterinary Medicine and Administration, Faculty of Veterinary Medicine , University of Warmia and Mazury in Olsztyn , Oczapowskiego 13 , Olsztyn , Poland
2. Department of Ichthyopathology and Fish Health Prevention , Stanisław Sakowicz Inland Fisheries Institute , Główna 48, 05-500 ¯abieniec , Poland
3. Department of Microbiology and Clinical Immunology, Faculty of Veterinary Medicine , University of Warmia and Mazury in Olsztyn , Oczapowskiego 13, 10-719 Olsztyn , Poland