Exploring Silver as an Alternative Treatment for Controlling Macrogyrodactylus congolensis Populations

Monogeneans are ectoparasites that in high densities, can cause harm and even death to their hosts. Therefore, treatment methods are continuously evaluated. The current study aims to determine the LC50 of ionic silver and silver-engineered nanomaterials (ENMs) (nAg) in the monogenean Macrogyrodactylus congolensis and report on the toxicological effects of silver on the parasite by using their behavioural response as an indicator. Macrogyrodactylus congolensis were exposed in vivo to a range of ionic Ag and nAg concentrations for 12 h in three water media (reverse osmosis [RO], borehole, and aged tap water). The LC10, LC20, and LC50 were determined using ToxRat Professional. Behaviour was assessed using low, medium, and high concentrations (calculated from the parasites LC50) of ionic silver and nAg in the different water media. Videos were recorded with a camera for 5-min periods at 0, 1, 3, 6, and 12 h intervals. The videos were analysed using Noldus EthoVision XT software. The results demonstrated significant increases in the acceleration of movement, body contact between parasites, the distance travelled, mobility, and swimming speed when exposed to increased concentrations of silver. Changes that have been observed are most likely in response to toxicological stress and neurological damage caused by silver. Furthermore, silver and RO water being the most toxic, and aged tap water is the most optimal water medium. Furthermore, parasites showed an increase in behavioural changes as exposure concentrations increased. Lower LCx values were recorded when parasites were exposed to the ionic Ag compared to the nAg in all water media, indicating that the ionic silver was more toxic to M. congolensis than nAg, which highlights the need for the safe development of nanotechnology.