Aqueous aluminium eliminates Gyrodactylus salaris (Platyhelminthes, Monogenea) infections in Atlantic salmon

This study focuses on the effect of acidic water and aqueous aluminium on t he monogenean ectoparasite Gyrodactylus salaris, infecting Atlantic salmon (Salmo salar) parr. G. salaris-infected salmon were exposed to various comb inations of acidity and aluminium concentrations. The most pronounced effec t was the elimination of parasites after 4 days when 202 mu g Al/1 was adde d to the water. The effect of aluminium was concentration dependent, but wa s relatively independent of pH (5.2, 5.6 and 5.9). At the lowest pH of 5.0 the effect of aluminium was enhanced. Acidic aluminium-poor water had no or minor effects oil the G. salaris infections except at pH 5.0 where all par asites were eliminated within 9 days. The G. salaris populations increased exponentially: in untreated control water. The results show for the first t ime that aqueous aluminium can, to a limited extent, have a positive effect on fish health. This study emphasizes that basic knowledge about abiotic e nvironmental factors is of importance in order to understand the population dynamics, range extension and dispersal of ectoparasites such as G. salari s. Finally, our results suggest that aluminium treatment could form an effe ctive disinfection method against ectoparasites in hatcheries and laborator ies, as well as complementing the controversial rotenone treatments used ag ainst natural populations of G. salaris.