1. H. Takahashi, H. Yamaguchi, and K. Ota: Uni Shubyou Seisan. Heisei 3 Nendo Annual Report, Iwate Northern Institute of Mariculture, pp. 5-31 (1991) (in Japanese).
2. 1) K. Kawamura: Uni Zouyoushoku to Kakou, Ryutsu, Hokkai Suisan Company, Sapporo, Japan, 1993, p. 82 (in Japanese).
3. 2) Y. Agatsuma: Strongylocentrotus nudus (A. Agassiz) Fishes and marine invertebrates of Hokkaido, “in Biology and fisheries” (ed. by K. Nagasawa and M. Torisawa), Sapporo, Hokkaido, 1991, pp. 330-333 (in Japanese).
4. 3) T. Sugimoto, K. Tajima, and K. Tomita: Reproductive cycle of the sea urchin, Strongylocentrotus nudus, on the northern coast of Hokkaido. Sci. Rep. Hokkaido Fish. Exp. Stn., 24, 91-99 (1982) (in Japanese).
5. 4) Y. Agatsuma, S. Motoya, and Y. Sugawara: Reproductive cycle and food ingestion of the sea urchin Strongylocentrotus nudus (A. Agassiz) in southern Hokkaido, I-Seasonal changes of gonad. Sci. Rep. Hokkkaido Fish. Exp. Stn., 30, 33-41 (1988) (in Japanese).