Herpes is suspected of taking a huge toll on cultured carp in 10 prefectures, according to findings reported Thursday to a farm ministry panel.

The first signs of carp dying were observed in fish farms in Lake Kasumigaura, Ibaraki Prefecture, in early October. The prefecture, which accounts for some 50 percent of farmed carp in Japan, reported that some 1,125 tons of carp had been lost as of Thursday. It said it had shipped farmed carp to 21 prefectures.

The fish were being bred at farms in Kasumigaura and Lake Kitaura. The dead fish were infected with the carp herpes virus.