Abstract <p>Since the beginning of the 21st century, the multiple cases of mass mortalities in populations of fish of <i>Carassius auratus</i> complex (Cyprinidae) have been noted from different regions of European part of Russia; however, the causes of those mortalities remained unexplained. We focused on mortality in a population of <i>C. auratus</i> complex in Kiovo Lake in the upper part of the Volga River basin. The presence of the emergent fish pathogen cyprinid herpesvirus 2 (CyHV-2) was confirmed by PCR in gill filament and muscle tissues of dead <i>C. auratus</i> complex individuals, but not in living conspecifics without clinical signs of diseases. This is the first detection of CyHV-2 in Russia. We encourage urgent investigations of possible links between the detected pathogen and mortality events in populations of <i>C. auratus</i> complex within Russia. Perspectives of using of CyHV-2 as a tool for biocontrol of <i>C. auratus</i> complex, one of the Top-100 invasive species in Russia, are discussed.</p>