抄録
Seasonal changes of the gonads of scallops, Patinopecten yessoensis (JAY), cultivated by the hanging method in Tôni Bay, Iwate Prefecture, were observed histologically. The gonad condition was classified into seven stages: I. undifferentiating stage (immature stage), II. Early differentiating stage (follicular stage), III. growing stage, IV. mature stage, V. spawning stage(partially spent stage), VI. post-spawning stage (completely spent stage) and VII. degenerating stage. Using this classification, the seasonal changes of the gonad condition of scallops, from one year until two years and two moths after birth during 1972-1973, was recorded. In Tôni Bay the gonad began to differentiate into oocytes or spermatocytes in September and increased in their volume, by the multiplication of the reproductive cells, in December and reached to mature conditions by February-March. Spawning seemed to take place during April-May. The reproductive cells that remained in the spent gonad degenerated or were absorbed during June-July. In the one-year-old specimens collected in May hermaphroditic gonads were present. Here spermatozoa and spermatids were surrounded by oocytes composed of follicle wall. The presence of hermaphrodism suggests that the scallop alters its sexual phase from male to female in the process of development. The mature or partially spent gonads observed in toe two year-old specimens, which were collected in July, 1973, indicated a fall in spawning activity and a non-synchronizing sexual maturation under the conditions of Tôni bay.
