The contributions of host age and size to the aggregated distribution of parasites in yellow perch, Perca flavescens, from Garner Lake, Alberta, Canada.

The independent effects of host age and size on parasite abundance are examined in yellow perch from Garner Lake in east-central Alberta. Older, larger perch tend to have more species of parasites combined with larger parasite infrapopulations. Sexual size dimorphism in perch generates 2 different size classes within each age class >2+ yr, thus allowing the opportunity to separate the effects of age and size on the recruitment of parasites by perch. The abundances of Diplostomum adamsi and Bothriocephalus sp. both increase with host age, whereas the increased abundances of Crepidostomum isostomum and Raphidascaris acus in larger fish are, in part, suggestive of size-specific feeding behaviors of the host. A combination of parasites with size- and age-dependent infrapopulations results in a size-dependent increase in infracommunity size. A comparison of variance-to-mean ratios within age classes to overall variance-to-mean ratios shows that the effects of host age and size on parasite recruitment do contribute to parasite aggregation.