1. Graduate School of Agricultural Science, Tohoku University, 468-1 Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi 981-8555, Japan
2. Seed Production Research Laboratory, Katsuura Sea Farming Section, Chiba Prefectural Fisheries Research Center, 178-17 Hamakatsuura, Katsuura, Chiba 299-5233, Japan
3. Tokyo Bay Fisheries Laboratory, Chiba Prefectural Fisheries Research Center, 3091 Kokubo, Futtsu, Chiba 293-0042, Japan