Age-, size-, and sex-specific infection of Anodonta piscinalis (Bivalvia: Unionidae) with Rhipidocotyle fennica (Digenea: Bucephalidae) and its influence on host reproduction

A Rhipidocotyle fennica infection in Anodonta piscinalis was studied during 1987–1989 in Lake Saravesi, central Finland. The overall prevalence was 32.3% (n = 1157). Only mature clams, ≥ 3 and ≥ 4 years old in the littoral and sublittoral zones, respectively, were infected. According to log-linear models constructed for the mature clams, there was a statistically significant interaction between prevalence and age of the host, between prevalence and habitat, and between age of the host and habitat; prevalences were higher among old specimens and in the littoral zone than among young clams or in the sublittoral zone. Logit models showed that prevalence increased linearly with host size in both habitats. A relationship between clam growth and infection was also found: fast-growing clams were more often infected or infected clams had grown faster. The quantity of sporocyst tubules increased with the age of the host. Prevalence was higher among female clams than among males. It was estimated that over 50% of mature females in the littoral zone were infected. It was also estimated that there was a 31% reduction in the number of glochidium-bearing clams in the littoral zone of Lake Saravesi due to infection with this parasite.