Changes in the site specificity of Gyrodactylus turnbulli Harris, 1986 (Monogenea) during infections of individual guppies (Poecilia reticulata Peters, 1859)

Gyrodactylus turnbulli Harris, 1986 infected the caudal peduncle (42% of all flukes) and caudal fin (40%), of guppies (Poecilia reticulata Peters, 1859), occurring less frequently on the pectoral (8%), dorsal (5%), pelvic (2%), and anal (1%) fins. This distribution of parasites on the fish and their crowding varied with infection age. On newly infected guppies, G. turnbulli occurred less frequently on the peduncle, and mean nearest-neighbour distance was not correlated with population size. Over the first 4 days of the infection the proportion of parasites on the peduncle increased to 60%, and mean nearest-neighbour distance became correlated with population size. In declining infections (day 6 onwards) the proportion on the peduncle declined, and mean nearest-neighbour distance increased independent of population size. This pattern suggests random colonization of the fins followed by migration to the peduncle, from which dispersal occurred during the declining phase of the infection.