Cercarial emergence was assessed by counting all cercariae that emerged from single periwinkles exposed to the different treatments. Periwinkles were collected in Årøsund, Denmark and screened in the laboratory to verify the infection status. To measure cercarial emergence, periwinkles were individually transferred from the jars into 50 mL Plexiglas beakers, one day after the 7-days acclimation (sampling 1), one week after the start of exposure to the treatments (sampling 2), and two weeks after the start of exposure to the treatments (sampling 3). Each incubation lasted eight hours. At the end of the incubation period, the water from each beaker was transferred into 50 mL Falcon tubes. In addition, the beakers were immediately washed with 5 mL ethanol (99%), and the solution was also added to the Falcon tube to ensure the collection of all cercariae and their preservation for later counting.