Influence of low temperatures on the cercarial shedding of Paramphistomum daubneyi from the snail Lymnaea truncatula

Lymnaeids in nature are subjected to temperature fluctuations that may have an influence on the shedding of cercariae. Thus, experimental infections o f Lymnaea truncatula by Paramphistomum daubneyi were performed to determine whether a sudden fail in temperature - daily dipping of infected snails in to spring water ai 14-15 degrees C, or at 6-8 degrees C - followed by its i ncrease at 20 degrees C in the subsequent hour, had an influence on the cha racteristics of snail infection and cercarial production. The immersion of infected snails in cold water during a short period delayed the first cerca rial shedding; at day 66 on average, in the 6-8 degrees C group vs at day 5 7 in the 14-15 degrees C group, or at day 49 in the 20 degrees C group. The percentage of cercaria-shedding snails was greater in the 6-8 degrees C gr oup than in the 14-15 degrees C and the 20 degrees C ones : 41.8 % vs 17.3 % and 7.1 %, respectively. The total number of cercariae given by each infe cted snail was also higher in the 6-8 degrees C group. A fall in the temper ature of water during daily change, followed by its increase at 20 degrees C within the subsequent hour, stimulated the cercarial shedding of P. daubn eyi.