Abstract
Mass mortality of carp Cyprinus carpio caused by koi herpesvirus disease (KHVD) occurred in seven rivers of Kanagawa Prefecture in 2004. Mortalities of KHVD peaked in May in four of the rivers (early outbreak group) and peaked in June in the other three rivers (late outbreak group). KHVD was first recognized at 15.5-18.5°C in the early outbreak group, and at 18.6-21.2°C in the late outbreak group. The temperature exceeded 15°C, which corresponds to the lowest temperature of the viral growth in cell culture.
