The influence of temperature and light on shedding of Diplostomum spathaceum cercariae from infected Lymnaea stagnalis, collected in a Danish trout farm, was determined and the cercariae were used in infection experiments with rainbow trout Oncorhynchus mykiss.Cercarial shedding was strongly temperature dependent.Thus up to 58 000 cercariae snail-' d-' were shed at 20°C and up to 10 000 cercariae snail-' d-l at 10°C; shedding was observed at a minimum temperature between 4 and 6"C, which is lower than previously recorded.At constant temperature (20°C) shedding was light and dark independent.The cercariae were infective at a temperature of 7°C although 4 to 5 times less infective than at 15°C.Migration of the diplostomulum larva inside the fish towards the eye lens was clearly influenced by temperature: after experimental exposure to cercariae, 50% of the larvae had accumulated in the lenses of rainbow trout within 26 h at 7°C and within 15 h at 15°C.
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Lyholt et al. (1996) studied this question.