Larval Pimephales promelas Rafinesque individuals, estimated to be 2 wk posthatch, from a small temperate lake in Algonquin Park, Ontario, were examined for parasites. The monogene Dactylogyrus pectenatus Mayes, 1977 was the only parasite found. Prevalence was 71.4%; mean intensity was 2.3 ± 1.7 (range 1–9). The presence of gravid parasites on fish measuring 12 mm in length suggests that the larvae became infected shortly after hatching, and because P. promelas is a fractional spawner, the larvae appear to represent a significant host resource for D. pectenatus during the summer months. The infection of this parasite on these larvae is discussed within the context of assembly of parasite infracommunities of fish.