Types and frequencies of pathologies were investigated in Crassostrea rhizophorae before and following heavy oyster mortality in Todos OS Santos Bay, Bahia, Brazil. The sporozoan Nematopsis sp. was the only parasite present in sufficient numbers to be an important mortality factor, but the intensity of Nematopsis infections remained low until after the major die-off. Pathologies such as ceroidosis, reduction or loss of stored glycogen, decreased gametogenesis, edema, and metaplasia of the digestive diverticula were consistent with the hypothesis of an external environmental stress factor that may have caused feeding to cease, the resultant weakness contributing to high mortalities. 8, 1986 Academic Press. Inc.

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SYNOPSIS.A haplosporidan parasite belonging to the genus Minchinia was found in 4 of 1,438 oysters, Crassostrea gigas, collected from the Republic of Korea. Multinucleated vegetative stages were present in the infected oysters. Spores found in one of these oysters were acid-fast and had operculate characteristics of the genus Minchinia.

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