Draining and liming of ponds as an effective measure for containment of CyHV-3 in carp farms.

Infections of common carp Cyprinus carpio and koi, its coloured morphotypes, with the cyprinid herpesvirus 3 (CyHV-3) can induce severe clinical signs and increased mortality in affected stocks. This may significantly challenge the economic basis of carp farming in Central Europe. To limit virus spread in carp farms, effective disinfection measures for ponds stocked with infected populations are required. In the traditional European pond aquaculture of carp, draining and liming of ponds with quicklime (CaO) up to pH 12 is a well-established disinfection measure against various pathogens. The present field study investigated whether these measures are sufficient for the inactivation of CyHV-3 infectivity in carp ponds. After draining and liming, the ponds were stocked with carp fry from a CyHV-3-negative stock, and 2 ponds were examined for the presence of CyHV-3-specific DNA sequences during the growth period of the carp and in the harvested stock. Wild fish (from the ponds, and feeder and drainage canals) and water samples (from the ponds) were also examined for CyHV-3-specific DNA sequences; and naïve carp were cohabited with wild fish, or exposed to the pondwater samples, to test for the presence of infectious virus. All examined samples remained negative for CyHV-3 throughout the study. This indicates that draining and liming with quicklime can be a suitable disinfection measure for ponds after a CyHV-3 outbreak in carp aquaculture.