Assessment of the toxicity of bio-synthesized silver nanoparticles on Oreochromis niloticus (Nile tilapia)

Silver nanoparticles (AgNPs) have garnered significant attention due to their antimicrobial properties. However, their potential environmental impact remains a concern. This study evaluates the acute toxicity and physiological effects of biogenic AgNPs synthesized using Aspergillus tubingensis (AgNP-AT) on Oreochromis niloticus (Nile tilapia), a widely used bioindicator species. AgNP-AT were characterized using UV-vis spectrophotometry (SPR peak at 420 nm), dynamic light scattering (DLS; 48 ± 5 nm), and transmission electron microscopy (TEM; 35 ± 10 nm). The 96-hours median lethal concentrations (LC₅₀) for AgNP-AT was determined as 8.8 μM, whereas AgNO₃ exhibited a significantly lower LC₅₀ of 0.028 μM, indicating its higher toxicity. Exposure to AgNP-AT at 30, 35, and 40 μM resulted in a significant increase in oxygen consumption (from 0.2 to 0.4 mL O₂ g⁻¹ L⁻¹ h⁻¹) without affecting ammonia excretion. Swimming activity was reduced in a concentration-dependent manner, with fish exposed to 40 μM showing the most pronounced impairment. Histopathological analysis revealed a reduction in lamellar length (50% decrease) and an increase in lamellar width (60% increase), demonstrating structural alterations in the gills. These findings show that AgNP-AT, although less toxic than AgNO₃, still induces physiological and morphological effects in Nile tilapia. This study provides valuable data for assessing the environmental risks of biogenic AgNPs and contributes to the development of safer nanotechnology applications.