1. Laboratory of Physiology, Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba 277-8564, Japan
2. Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo 113-8657, Japan
3. Department of Life Sciences, Toyo University, Oura, Gunma 374-0193, Japan
4. Ibaraki Prefectural Oarai Aquarium, Oarai, Ibaraki 311-1301, Japan