^​Hyoun Joong Kim¹, Jin Woo Jun², Sib Sankar Giri¹, Saekil Yun¹, Sang Guen Kim¹, Sang Wha Kim¹, Jeong Woo Kang¹, Se Jin Han¹, Jun Kwon¹, Woo Taek Oh¹, Hyung Bae Jeon³, Cheng Chi⁴, Dalsang Jeong² and Se Chang Park<sup>*,1

1</sup> Laboratory of Aquatic Biomedicine, College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul 08826, Republic of Korea
² Department of Aquaculture, Korea National College of Agriculture and Fisheries, Jeonju 54874, Republic of Korea
³ Department of Life Science, Yeungnam University, Gyeongsan 38541, Republic of Korea
⁴ Laboratory of Aquatic Nutrition and Ecology, College of Animal Science and Technology, Nanjing Agricultural University, Nanjing 210095, China

^*Correspondence : Se Chang Park, College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul 08826, Republic of Korea.

Summary
Since November 2017, mass mortalities of larvae of bay scallop (Argopecten irradians) were reported in hatcheries located at the southern area of Republic of Korea. Over 90% of larvae aged 5 to 10 days sank to the bottom of the tank and died. The hatcheries could not produce spat and thus artificial seed production industry incurred huge losses. We identified Ostreid Herpesvirus‐1 μVar (OsHV‐1 μVar) associated with mass mortality by PCR, sequencing and transmission electron microscopy (TEM). All the samples were positive for OsHV‐1 μVar with 99% sequence identity to previously reported OsHV‐1 μVar sequences. Partial sequence of ORF‐4 of OsHV‐1 detected in this study was more closely related to sequences isolated from Europe. This is the first report to confirm the mortality caused by an OsHV‐1 infection in the bay scallop.

Keywords : Ostreid Herpesvirus‐1 μVar (OsHV‐1 μVar), mass mortality, bay scallop (Argopecten irradians) larvae