Occurrence of Perkinsus species (Protozoa, Apicomplexa) from Manila clam Tapes philippinarum in Japan

Abstract

In April 1998, unidentified parasites were found in Manila clam Tapes philippinarum in an inner bay of the western part of Japan. Ray's fluid thioglycollate medium (RFTM) culture of tissues from infected Manila clams yielded prezoosporangia of the parasite. Many free motile zoospores were released from the prezoosporangia when they were transferred to seawater. Histologically two types of trophozoites were observed: cells in a cluster and free single cells. They were found in the digestive gland, gill, mantle and foot of the clam. In immunohistochemical assays using an antiserum against Perkinsus marinus, the antibody reacted to both types of trophozoites. These results indicated that these parasites in Manila clam were species belonging to the genus Perkinsus. However, they differed from previously described species in the morphology of trophozoites and prezoosporangia.