アサリ養殖における有害動物としてのカクレガニの生態-II

Abstract

The present paper is a record of the ecological observations of Pinnotheres sinensis as pest in culture of Tapes japonica and the influence of the crab on the weight of the host's flesh. It was not observed that two or more female crabs were living in one host. Few male crabs were observed in host and five living with female were found among thirty-seven crabs. One of the writers caught a male crab walking on the outside of the mussels (Mytilus edulis) in the field. The berried crabs were found from July to October, exceptionally in June and December (Fig. 1) but the optimum hatching season ran from September to October at water temperatures ranging from 24°C to 19°C. From next May to July many young crabs were found in the host (Fig. 2) and they became to berry in Autumn. The biological minimum size was 5.3mm in carapace length. Large crabs (over 8mm) began to decrease in number from summer. The size of berried crabs varied in accordance with the period in breeding season. The highly infested region with Pinnotheres sinensis was situated along the channel (Fig. 3). In the laboratory, some female crabs free from the host were possible to live fairly long time viz. 4-6 months. Tapes japonica infested with Pinnotheres sinensis was lean without regard to their size or season (Fig. 4, 5).