Effects of altered water quality and trace elements on the infection variables of Paradiplozoon ichthyoxanthon (Monogenea: Diplozoidae) from two sites in the Vaal River system, South Africa

Using parasites as sentinel organisms has received increased attention due to their responses toward environmental degradation. In some sections of the Vaal River, South Africa, water quality is altered and biota distribution affected. The aims of this study were to assess and compare infection variables of Paradipolozoon ichthyoxanthonAvenant-Oldewage, 2014 in Avenant-Oldewage et al. (2014) at two sites along the Vaal River and compare the water quality and trace element levels at the sites. Infection variables of the parasite, physico-chemical variables, and sediment and water samples for trace element analysis were collected at each site. Conductivity and trace element concentrations were higher at the Vaal River site than the Vaal Dam. Temporal variances in water quality and parasite prevalence, mean intensity and mean abundance, at intervals over a 14 year period occurred, P. ichthyoxanthon was absent at the Vaal River site though the host fish are present. Prevalence peaks in summer and winter. Comparison of infection data to water quality and trace elements indicated that conductivity and trace element levels negatively affected/correlated with the infection variables. Higher trace elements concentration and conductivity at the Vaal River site are thought to be driving factors responsible for absence of the parasite.