Anti-parasitic efficacy of green-synthesized silver nanoparticles on Argulus siamensis: An ectoparasite of fish and their effect on the expression of ion channel genes

Argulosis, a serious fish disease caused by the crustacean ectoparasite Argulus, results in considerable losses to the global aquaculture industry. This study evaluated the in vitro anti-parasitic efficacy (AE%) of synthesized silver nanoparticles (AgNPs) using an aqueous leaf extract of Azadirachta indica (neem) against the adult and copepodid stages of Argulus siamensis. The biosynthesized AgNPs were characterized using UV–Vis spectroscopy, which revealed a surface plasmon resonance peak at 425 nm, with a zeta potential value of − 28.5 mV. TEM analysis verified that the nanoparticles were ranging from 5 to 50 nm in size, spherical in shape, and capped by various phytochemicals identified through Fourier-transform infrared spectroscopy (FTIR). Treatment with AgNPs showed an AE of 100% against copepodids at 25 ppm and adult Argulus at 50 ppm, with an estimated 6-h EC₅₀ of 9.66 and 16.03 ppm, respectively. No mortality was found in the control, leaf extract, and AgNO₃-treated groups of parasites. Additionally, gene expression studies using β-actin as a reference gene revealed significantly upregulated levels of all tested genes, with the highest fold change in the GABA gene across all treatment groups. The increased AE of AgNPs may be due to altered signal transduction, as evidenced by the significantly increased expression of ion channel genes compared to control and neem leaf extract-treated groups. The findings of this study indicate the potential for developing a promising nanodrug for the safe and effective control of argulosis in aquaculture systems.