Assessing ionic silver and nano silver as emerging treatments for monogenean infections on clarias gariepinus in aquaculture

Title : Assessing ionic silver and nano silver as emerging treatments for monogenean infections on clarias gariepinus in aquaculture

Abstract:

Monogenean ectoparasites such as Macrogyrodactylus congolensis pose health and production challenges for Clarias gariepinus in aquaculture facilities. Heavy infections of these parasites lead to epithelial damage, excess mucous, haemorrhage and in some cases mortality. Conventional treatments, such as formalin, salt, and praziquantel, are often ineffective against all life stages, highlighting the need for alternative control strategies. Silver is a recognised antimicrobial agent and has recently also been used as an effective antiparasitic. This study assesses the efficacy of AgNO₃ and nAg by integrating lethal concentrations and reproduction of the parasite, in combination with observations of the tegument integrity of the parasite and host. Parasites were exposed in vivo to a range of AgNO₃ and nAg concentrations for 12 hours, and the LC₁₀, LC₂₀, and LC₅₀ values were calculated using ToxRat®. Reproduction and survival of the parasite were assessed both off (acute tests) and on the host (chronic tests). Tegument damage and the presence of silver were confirmed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Off-host exposures showed a concentration-dependent effect with higher concentrations (≥ 50 µg/L AgNO₃, ≥ 20 mg/L nAg) inhibiting parasite reproduction. On-host LC₁₀ exposures caused an initial increase in parasite reproduction followed by moderate inhibition of parasite reproduction thereafter. SEM analysis showed pathology characterised by vacuoles, punctures and shrivelling, in both the parasites and the host's tegument exposed to both forms of Ag, with AgNO₃ causing more observable damage. The EDS analyses confirmed Ag accumulation on the parasite’s tegument following exposures. Findings from the current study suggest that Ag shows potential as a treatment for managing M. congolensis infections in aquaculture systems, but the damage to host epithelia suggests that the stress effect on the host requires further attention and risk analysis to evaluate parasite pathology versus treatment pathology.

Biography:

Lutfiyya Latief is a PhD candidate in the Zoology department at the University of Johannesburg, South Africa, specialising in Aquatic Fish Parasitology and toxicology resulting from treatment. Her research focuses on the uses and impacts of ionic silver and nano silver on the African sharptooth catfish (Clarias gariepinus) and its monogenean parasite (Macrogyrodactylus congolensis).