Dynamics of challenge infections of Gyrodactylus bullatarudis Turnbull (Monogenea) on guppies, Poecilia reticulata (Peters)

Comparison of the population dynamics of Gyrodactylus bullatarudis o fish that were reinfected at 0, 1, 2, 4, or 6 weeks post‐recovery from an initial, infection were based on the following parameters: percentage establishment, recovery and death, mean peak parasite burden, mean time to peak burden, mea duration of infection, mean time to death. Of fish that recover from an initial, infection, some are immediately susceptible to a challenge infection. Other fish are able to harbour a challenge infection hut parasite numbers increase less and the infection is of shorter duration than the initial. These fish regain their fu susceptibility within 4‐6 weeks post‐recovery. A third group of fish become totally refractory to reinfection and only slowly regain their ability to support an infection Thus even at 6 weeks post‐recovery they are only partially susceptible t reinfection. It is probable that the three groups in fact represent a continuum increasing susceptibility to challenge infection.