Dynamics of a fish ectoparasite population: opportunistic parasitism in Argulus japonicus (Branchiura)

In the Bloemhof Dam, Transvaal, South Africa, Argulus japonicus demonstrated an opportunisitc nature in its reproductive strategy and proved to be highly mobile. Labeo capensis was the preferred host (even though not the most abundant fish), but the parasite was found on all fish present in the dam. Infestation is linked with immune response of the putative host, accessibility through feeding habits, and the daily and seasonal movements of the hosts. The parasite population showed stability in both structure (male:female ratio sometimes over 3:1), though approaching unity when the bulk of females were gravid) and age distribution. Fresh cohorts were noted each month during spring and summer; eggs seem to be temperature-limited in autumn and winter. -P.J.Jarvis