Tun Kay Lwin, Itoh Naoki, Ueki Noriyuki, Yoshinaga Tomoyoshi, Ogawa Kazuo
Laboratory of Fish Diseases, Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
J Invertebr Pathol. 2007 Nov;96(3):205-12. doi: 10.1016/j.jip.2007.06.001. Epub 2007 Jun 16.
Marteilioides chungmuensis, a protozoan paramyxean parasite, infects the oocytes of the Pacific oyster, Crassostrea gigas. The effects of infection on the reproductive cycle of C. gigas were investigated over two consecutive years at Okayama Prefecture, Japan. In male oysters, gonadal development began during February/March, maturity was achieved in June and spawning activity extended from July to September. In November and December, male oysters were not seen, probably because their gonads regressed to connective tissue and they transformed into undifferentiated oysters. By contrast, female oysters, in which parasite spore formation occurred, were still carrying oocytes until the following March and the spawning process of female oysters took 5 months longer than that of males in epizootic areas. The prevalence of M. chungmuensis infection increased from July to September, when most female oysters had their spawning period, and declined from October to the following April when oysters were at the spent stage. The prevalence of infection increased again in May of the following year and high prevalence was observed in the following July. When prevalence was compared between oysters of different age classes, higher prevalence was detected in older than in younger oysters. Histological examination showed that infected oysters produced oocytes continuously and spawned repeatedly from October to March, during which period healthy oysters were reproductively inactive. Parasites can infect the oocytes of infected oysters throughout the longer spawning period. These observations suggest that M. chungmuensis extends the reproductive period of infected oysters for its own reproductive benefit.
忠武拟马尔太虫（Marteilioides chungmuensis）是一种原生动物类的单孢子虫寄生虫，可感染太平洋牡蛎（Crassostrea gigas）的卵母细胞。在日本冈山县连续两年研究了该寄生虫感染对太平洋牡蛎生殖周期的影响。在雄性牡蛎中，性腺发育始于2月/3月，6月达到成熟，产卵活动从7月持续至9月。11月和12月未见雄性牡蛎，可能是因为它们的性腺退化为结缔组织并转变为未分化的牡蛎。相比之下，发生寄生虫孢子形成的雌性牡蛎，直到次年3月仍携带卵母细胞，在疫区雌性牡蛎的产卵过程比雄性长5个月。忠武拟马尔太虫感染率从7月至9月上升，此时大多数雌性牡蛎处于产卵期，10月至次年4月下降，此时牡蛎处于耗尽期。次年5月感染率再次上升，次年7月观察到高感染率。当比较不同年龄组牡蛎的感染率时，发现年龄较大的牡蛎感染率高于年龄较小的牡蛎。组织学检查表明，受感染的牡蛎从10月至3月持续产生卵母细胞并反复产卵，在此期间健康的牡蛎生殖不活跃。在更长的产卵期内，寄生虫可感染受感染牡蛎的卵母细胞。这些观察结果表明，忠武拟马尔太虫为了自身繁殖利益延长了受感染牡蛎的繁殖期。
