Laboratory studies of parasite transmission aspects between Hydrobia spp. (Gastropoda) and Corophium volutator (Amphipoda)

Aspects of parasite transmission between Hydrobia spp. and Corophium voluta tor, first and second intermediate host of digenetic trematodes, were inves tigated under laboratory conditions. H. ventrosa is used as an intermediate host by several trematode species. Under laboratory conditions the most fr equently observed emergence from H. ventrosa was of cercariae of Maritrema subdolum. The number of cercariae shed per day varied considerably. It was observed that 30 cercariae on average and up to 450 cercariae at maximum ca n emerge from a single H. ventrosa per day. Cercarial production continued until the death of the snails. The life-span of cercariae of the species M. subdolum decreased as the water temperature increased. It can be concluded that under natural conditions the cercariae, after emerging, have a maximu m period of 1 day in which to seek out their second intermediate host C. vo lutator. Almost all specimens of C. volutator exposed to cercariae of the s pecies M. subdolum died within the test period of 6 days. High average cerc arial densities caused short life-spans (<50 h), while at lower densities l onger survival times were possible. For cercariae of other Trematoda specie s, we were unable to find any equally clear evidence of a reduction in the survival rate of C. volutator within the test period. Mortality of C. volut ator, and other effects of infestation, as observed in our experiment, can be assumed to be a result of the penetration process of the cercariae but t hey also can be attributed to the mesocercariae.