ABSTRACT: 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 58000 cercariae snail^-1 d^-1 were shed at 20*C and up to 10000 cercariae snail^-1 d^-1 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.

KEY WORDS: Eye flukes . Rainbow trout . Diplostomum . Lymnaea . Cercarial shedding . Temperature . Light

Published in DAO Vol. 25, No. 3 (1996) on June 6
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1996