Effects of low salinity in ambient water on ventilation volume, ciliary movement and survival rate were examined in the pen-shell Atrina (Servatrina) lischkeana. When the salinity decreased, the pen-shell converted the continuous ventilation to the intermittent one under the hypoxic condition, but it maintained the continuous ventilation under the normoxic dissolved oxygen condition. The ventilations both under the hypoxic condition and under the normoxic condition declined with decrease in salinity, and finaly stopped at salinities of 19.3-23.5 psu. The pen-shell still opened the shell valves after stopping the ventilation. The transportation velocity of a small piece of vinyl film on the gill surface, which represented the ciliary movement velocity indirectly, decreased as the salinity declined, and showed 0 mm/min at 10 psu. The survival rate at 15 psu or above for 96 hours was 100%, that at 10 psu for 24 hours was 0%.