Effects of cadmium and zinc toxicity on orientation behaviour of Echinoparyphium recurvatum (Digenea: Echinostomatidae) cercariae

Abstract

The effects of cadmium and zinc toxicity on orientation behaviour (photo- and geo-taxis) of Echinoparyphium recurvatum cercariae was investigated at concentrations ranging from 10 to 1000 μg l-1. Exposure to the toxicants at all metal concentrations caused a change in orientation to negative phototaxis and positive geotaxis during the sub-maximal dispersal phase (0.5 h cercarial age). Autometallography staining of cercariae exposed to 1000 μg l-1 cadmium or zinc showed selective binding of heavy metals to tegumental surface sites associated with sensory receptors. The significance to parasite transmission of changes in cercarial orientation behaviour in metal polluted environments is discussed.