Each snail was subsequently examined for trematode
infections by testing for cercarial shedding twice within a week.
Prior to cercarial shedding, the snails were cleaned with
dechlorinated tap-water. Shedding was induced under 25 W
electric light bulbs for 2 hours at room temperature during the
day. For species that shed cercaria at night, black covers were
used to achieve total darkness and snails were allowed to shed
overnight. Uninfected snails were soaked in phosphate
buffered saline (PBS) containing antibiotics (200 unit/ml of
penicillin and 100 μg/ml of streptomycin) for 3 to 4 hours before
extraction of DNA to ensure that bacterial contamination was
minimized.