Exposure to a Mixture of Zinc and Copper Decreases Survival and Fecundity of Discocotyle sagittata (Leuckart) Parasitizing Juvenile Atlantic Salmon, Salmo salar L.

We assessed the effects of zinc and copper on freshwater monogenean ectoparasites (Discocotyle sagittata Leuckart) infecting juvenile Atlantic salmon (Salmo salar L.). Exposure to 47 μg/L zinc and 3 μg/L copper reduced survival and fecundity of adult D. sagittata, while egg hatching success was only reduced at high exposure concentrations (2704 μg/L zinc and 164 μg/L copper). Parasitized salmon had decreased plasma chloride, but this was negated in infected fish exposed to metals. No other effects on Atlantic salmon survival and physiology (plasma osmolality, hematocrit) were noted, suggesting that D. sagittata may be more susceptible to metal toxicity than its host fish.