1. Laboratory of Veterinary Pathology, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555, Japan
2. United Graduate School of Veterinary Sciences, Gifu University, Gifu, Gifu 501-1193, Japan
3. Laboratory of Veterinary Pathology, Iwate University, Morioka, Iwate 020-8550, Japan
4. Izu-Mito Sea Paradise, Numazu, Shizuoka 410-0224, Japan
5. Wakkanai Fisheries Research Institute, Hokkaido Research Organization, Wakkanai, Hokkaido 097-0001, Japan
6. Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan