| Summary: | 碩士 === 國立臺灣海洋大學 === 環境生物與漁業科學學系 === 102 === In this study, samples of Polyascus plana parasitic on Metopograpsus thukuhar were collected from northern Taiwan since October 2011 to August 2013. To study about the parasitic situations and developmental stages.
The prevalence average is 55.68%. The lowest prevalence is 23.81% on the end of May 2012 and the highest is 80.65% on the mid-August 2012. The host sex ratio was 1.17 (male 135 : female 115).Parasitized females the abdomen width are not changed but parasitized males are different. Males the abdomen become feminized that is flat and wide. According to the parasitized males the abdomen morphological are changed that can be divided into four types. In this study uses analysis of covariance (ANCOVA) to test the different sexual that carapace width and 4-5 abdomen segment wide. The results show that females are not difference between normal and parasitic but there are significant differences between parasitized and normal males.
Single host can carry on seven externae on the same time. However the normal situations are following: (1) there are not externa but scar that after externa dead. (2) there is only one externa. (3) There are two externae. Those percentage are 34%, 32 % and17.6%. The host with multiple externae are appeared from March and the most numbers come in August and September in 2012. Then it is decreased to the lowest in December in 2012. There were not collected on January and February in 2013. Hosts still can molt after they be parasitized. The externae can be divided into four different development stages :(1)virgin externa stage, (2)immature externa stage, (3)mature externa stage and (4)mature externa release larvae stage. According to the Monthly changes that is number of externae, externae of the developmental stage, external tissue sections and external hatchling larvaes number, the study suggests the reproduction season of P. plana in March to December and each externa could have several reproduction cycles. A period of single production is around 15 days.
The experiment of lab showed that the larval development period was around 44hr in 25℃. The number and sex ratio of larvae from single externa varies with seasons, over 90% female larvae in summer but almost male larvae is in the winter that percentage is approximately 97%.
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