抄録
Gonad development of one-year-old scallops, Patinopecten yessoensis (JAY), cultivated in Yamada Bay, Iwate Prefecture, during August, 1973-January, 1974, was studied by histological methods and observations compared with that in Tôni Bay. The results obtained are as follows.
(1) One-year-old scallops collected in May, 1973, possessed mature testes or ovaries. These show that not only the males but also the females can reach to gonad maturation within one year after birth. Among them were observed specimens possessing hermaphroditic gonad, which suggest sexual phase alternations in the progress of development.
(2) During June-August, the control specimens collected in Tôni Bay were in an immature stage and the remaining reproductive cells had degenerated and had been absorbed completely, while many specimens in Yamada Bay possessed mature or partially spent gonads.
(3) The maintenance of mature gonad condition in summer was more remarkable in the area with high mortality. This suggests that the abnormal condition of the gonads is one of the important factors causing mass-mortality in Yamada Bay.
