Under natural conditions, the emergence of Opisthorchis viverrini cercariae from naturally infected
Bithynia (Digoniostoma) siamensis goniomphalos showed diurnal periodicity, peaking between 8:00-10:00 AM.
The cercariae did not emerge during darkness, but low-intensity light could induce a release. Cercariae shedded
from each field infected B.(D.) s. goniomphalos was recorded daily. The maximum output from one snail was
1,728 cercariae in a day. The total cercarial output from all five infected snails was 56,555 and the maximum of
total cercariae shed from one snail was 27,692. The field-infected B. (D.) s. goniomphalos could survive for 70
days after the snails were collected.