The invasion route of the gill parasite Urocleidus adspectus Mueller, 1936 (Monogenea: Ancyrocephalinae)

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Abstract
U. adspectus is transmitted experimentally to yellow perch (Perca flavescens) and the route of invasion and the behavior of the parasite during migration to the host gills is studied. The oncomiracidia invade the full length of the host and, attach at secluded sites such as beneath scales, at the base of fins, and in nooks in the body surface. The postoncomiracidia gradually migrate anteriorly and reach the gills by entering the opercular cavity and possibly the buccal cavity. In young-of-the-year perch, migrating worms appear to invade the primary lamella from the base or from the distal tip. In older perch the majority appear to invade the primary lamella from the base. Of the postoncomiracidia > 90% reach the gills of the young perch by day 5 postinfection and experimental studies indicate that few worms are dislodged during the migration.