This study examines the effects of aqueous metals on two ectoparasites; Gyrodactylus derjavini and Gyrodactylus magnificus. The experimental metals used, were aluminium (200 µg Al/l), zinc (400 µg Zn/l), copper (40 µg Cu/l) and nickel (5000 µg Ni/l). The fish hosting the parasites, were naturally infected and exposed to each metal (pH between 5, 6 and 6, 4) and control water (pH between 6, 1 and 6, 5) in separate experimental units (n = 10 in each unit). The results showed that aqueous aluminium, zinc and nickel had a negative and eliminating effect on the parasite populations without noticeable harming the hosts. There were no significant difference between parasites exposed for control water and those exposed to aqueous copper, although there was a slight reduction in parasite prevalence (%-amount infected fish) within the population exposed for copper. The effects of aluminium, zinc copper and nickel on the gyrodactylids in this present study confirms the results and experiences from previous studies on gyrodactylids. Finally, this study contributes with new knowledge regarding water quality criteria on the matter of mortality of ectoparasites. This is the first documented result on experimental effects regarding aqueous nickel and its strong reducing effect on a gyrodactylid; G. magnificus.
Keywords: Aqueous meals; Aluminium, Copper, Zinc, Nickel; Ectoparasites; Gyrodactylus; Water quality.