Impacts of an invasive virus (CyHV-3) on established invasive populations of common carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis>) in North America

The effects of invasive pathogens on wild fish and fish communities generally are not well documented. We compiled information on the impacts of mass mortality events due to Cyprinid Herpesvirus-3 (CyHV-3), otherwise known as Koi Herpesvirus, on wild North American populations of the invasive cyprinid, Cyprinus carpio (common carp), based on our personal experiences, discussions with North American fish ecologists and virologists, a detailed survey of technical and popular publications and a web search. We found evidence of 17 mass die-offs of carp due to CyHV-3 in North America since 2004, for 7 of which we were able to obtain information about carp before and after the events. For 6 of the events, effects of the die-offs on carp population indices appeared to be slight. Carp size-frequency distributions before and after the well-documented 2007/08 event in Ontario were also not conspicuously different. The exceptional event was at Blue Springs Lake, Missouri, in 2012, at which we estimate 65% of the carp present died as a result of CyHV-3 infections and carp abundance continues to decline. Why Blue Springs Lake differs from other events in North America is not clear. Overall, carp die-offs due to CyHV-3 in North America (1) confirm laboratory studies that only common carp are affected, (2) are of brief duration (3–6 weeks), (3) are not repeated in subsequent years and (4) cause much lower mortality (with the exception of Blue Springs Lake) than previously reported for carp in aquaculture facilities or in the laboratory. In terms of both wild carp and their effects on aquatic communities, the short and long-term effects of most die-offs appear to be slight. These features could have implications for the effectiveness of the proposed use of CyHV-3 to reduce feral carp populations in Australia.