THE ECOLOGY OF DIPLOSTOMUM-PHOXINI INFECTIONS IN 2 MINNOW (PHOXINUS-PHOXINUS) POPULATIONS IN SCOTLAND

Data are presented on the infection dynamics of the brain-dwelling met acercariae of Diplostomum phoxini (Digenea: Trematoda) parasitizing Eu ropean minnow (Phoxinus phoxinus) populations in a lowland river (Rive r Endrick) and a highland loch (Loch Maragan) in central Scotland. Pre valence of the parasite approached 100% in all samples taken from both populations over a la-month period, and within each population the in tensity of infection increased with increasing host fork length. Howev er, the two relationships differed, and size-matched minnows from the Endrick exhibited significantly higher intensities than those from Loc h Maragan, suggesting that metacercarial acquisition occurred at diffe rent rates in the two populations. Data regarding seasonal trends in t he acquisition of D. phoxini indicated that fish in both populations b ecome infected with the parasites mainly during the spring and summer, with negligible infection occurring during winter months. Analysis of size-matched fish from individual samples revealed apparent differenc es in the distribution of D. phoxini within the two host populations. Whereas D. phoxini metacercariae appeared to be overdispersed amongst length-matched fish from Loch Maragan samples, the parasite was distri buted normally amongst fish from the Endrick. Possible reasons for the observed differences in the infection characteristics of D. phoxini i n the two minnow populations are discussed, with reference to the para site's transmission dynamics and local environmental conditions.