Infection levels of Pekinsus olseni in Manila clam Ruditapes phillipinarum much vary among different locations. In order to know the effects of environmental factors on the infection of the parasite, we maintained Manila clams at different salinities (15, 18, 21 and 30 psu) and temperatures (13°C, 18°C and 23°C) after challenge with parasites and examined the infection intensities in the clams at intervals. In clams maintained at different salinities, no association was detected between salinity and infection intensity except that the intensity was significantly lower at 15 psu than at any other salinities on 54 day post challenge only, when the experiment was terminated. A significant difference was observed in the survival rate of clams between challenged and control groups at 30 psu only, suggesting that the negative effect of P. olseni on the survival of clams was attenuated with decreasing salinity. In clams maintained at different temperatures, the infection intensity little changed at 13°C, although it increased remarkably at 18°C and 23°C. The result indicates that in-vivo propagation is suppressed at 13°C and lower. A significant decrease was observed in the survival of clams at 23°C only, indicating that the virulence of P. olseni depends on temperature.
2015 The Japanese Society of Fish Pathology