Antiparasitic efficacy and safety evaluation of green-synthesized silver nanoparticles as sustainable nanotherapeutics against Argulus siamensis in Labeo rohita.

Argulosis poses a major challenge to freshwater aquaculture, and the use of conventional chemotherapeutics is increasingly constrained by environmental and sustainability concerns. In this study, silver nanoparticles were synthesized using Azadirachta indica (neem) leaf extract and evaluated for their antiparasitic efficacy (AE) against Argulus siamensis infesting Labeo rohita. Neem leaf-synthesized silver nanoparticles (NL-AgNPs) showed a characteristic surface plasmon resonance peak (λ_max) at 420 nm and a zeta potential of -28 mV, indicating good stability. The nanoparticles were spherical in shape with an average size of 20 ± 5 nm. FTIR analysis confirmed the presence of functional groups responsible for nanoparticle reduction and stabilization. An acute toxicity test of NL-AgNPs in L. rohita revealed a 96-h LC₅₀ of 28.25 mg L⁻¹ , with no observed mortality in the control group. The in vivo exposure to NL-AgNPs resulted in concentration-dependent AE of 36, 75, and 100% at 7.05, 14.12, and 21.19 mg L⁻¹ , respectively, with a 96-h EC₅₀ of 9.12 mg L⁻¹ and a therapeutic index of 3.10. Environmental scanning electron microscopy showed dose-dependent nanoparticle deposition on the parasite surface, causing severe structural damage and resulting in parasitic death. ICP-OES analysis following 14 days of exposure showed significantly higher silver accumulation in the liver (0.430 µg g⁻¹) than in the gills (0.31 µg g⁻¹), following a dose-dependent trend. Further, the comet assay demonstrated a concentration-dependent increase in DNA damage with % DNA in tail values of 15.49% (tail length: 6.35 px) and 7.27% (tail length: 4.63 px) at 21.19 and 14.12 mg L⁻¹ , respectively. Histopathological analysis further revealed substantial restoration of Argulus -induced tissue damage in the gills, liver, muscle, and kidney of L. rohita following NL-AgNP treatment. Overall, green-synthesized AgNPs demonstrate promising antiparasitic effects against Argulus siamensis, with mild toxic responses observed in Labeo rohita under the tested conditions. However, further investigations addressing chronic exposure, bioaccumulation, and depuration dynamics are necessary to evaluate the long-term safety and sustainability of NL-AgNPs applications in aquaculture.