Impact of aqueous exposure to silver nanoparticles on growth performance, redox status, non-specific immunity, and histopathological changes of Nile Tilapia, Oreochromis niloticus, challenged with Aeromonas hydrophila

Silver nanoparticles (AgNP) are one of the most synthesised nanomaterials due to their widespread applications, which in turn increases the potential of release and accumulation in nature. Moreover, they are known as antibacterial and recommended to be used in different commercial drugs. However, the evaluation of their effect on living organisms, especially fish, at low levels is still not completely understood. Therefore, the present study was conducted to investigate the effects of aqueous exposure of AgNPs on growth performance, oxidative status, non-specific immunity, and histopathological changes of epidermis, gills, liver, and intestine of Nile Tilapia, Oreochromis niloticus. The fish were exposed to four concentrations of AgNP (0, 10, 20, and 30 mu g L-1) for 8 weeks. At the end of the experiment, fish were intraperitoneally injected with pathogenic bacteria Aeromonas hydrophila and fish mortalities were recorded up to 14 days post-challenge. The results revealed that growth performance and feed utilisation of fish exposed to the lower AgNPs concentration improved significantly compared to other treatments. The increasing AgNP exposure levels decreased different growth indicators in a dose-dependent manner. The highest catalase, superoxide dismutase, glutathione peroxidase, lysozyme, and respiratory burst activities were recorded with 10 mu g AgNPs L-1 and the enzyme activities were retarded with increasing AgNP concentrations. The total bacteria count in the water decreased with increasing AgNP concentrations. Meanwhile, the relative percentage of survival improved with low AgNP concentration and decreased with increasing exposure levels. The histopathological investigation of different studied tissues (gills, skin, liver, and intestine) revealed an increase of histological lesions' frequency and severity with increasing AgNP concentrations. It can be concluded that the exposure of Nile Tilapia to AgNP at levels exceeding 10 mu g L-1 could interrupt growth performance, immunity, and antioxidant status and induced histopathological changes.