Over a 10-month period, cultured oysters (Crassostrea rhizophorae and Crassostrea gigas) from Ponta do Sambaqui, Florianopolis, Santa Catarina State were evaluated microscopically and histologically for parasite infection. Thirty mature individuals of each species were examined each season, for a total of 240 oysters. The animals, which originated from laboratory spawning, were kept in culture lanterns suspended in long-line systems at a density of 40 oysters per floor. Mortality, water temperature (19 to 28.5 ºC range) and salinity (31 to 35‰) were recorded at each sampling. The total amount of dead oysters was 58 (48.3%) to C. gigas and 85 (70.8%) to C. rhizophorae. All C. gigas individuals were infected with polydiariosis parasites (100%) throughout the experimental period; whereas 100% infection of G. rhizophorae with polydiariosis was observed only in February and May. "Foot disease" was detected in 3.3% of C. gigas oysters in November and in 23.3% of C. gigas and 6.6% of C. rhizophorae oysters in May. The highest incidences of Nematopsis infection were 70% and 60% in C. gigas and C. rhizophorae, respectively. Trichodina protozoa occurred in 1.6% of G. rhizophorae individuals; while Tylocephalum cestoda larvae were found in 2.5% of C. gigas individuals examined. Total mortality percentages of 48.3 in C. gigas and 70.8 in C. rhizophorae could not be associated with parasite infection.
oyster; Crassostrea; histopathology; parasite
