Abstract <p>Prebiotics play a vital role in aquaculture by promoting gut health and enhancing the immune response of fish, leading to greater disease resilience. This study focused on the toxic effects of silver sulfate on the mucus parameters, liver, and gill tissues of Nile tilapia (<i>Oreochromis niloticus</i>) fed with oyster mushroom (<i>Pleurotus ostreatus</i>) powder as a prebiotic. A total of 120 Nile tilapia fingerlings, averaging 20 ± 5 g, were acclimated under controlled conditions, with monitored water quality. The experiment included a control group and three treatment levels of prebiotic (0.05, 0.1, and 0.2%) mixed with commercial feed. Lethal concentrations of silver sulfate were determined through a 96-h exposure, followed by a sub-lethal toxicity test at 10% of LC50. Tissue samples from the gills and liver were collected for histological analysis, while immune parameters from mucus samples were assessed. Results indicated significant gill tissue damage in the control group, while the prebiotic treatments reduced this damage, particularly in the 0.05% group. Liver injuries were also less severe in the prebiotic-fed groups, with notable protection at the 0.2% level. Immune parameters, including lysozyme, total protein, alkaline phosphatase, and immunoglobulin levels, were significantly improved in the prebiotic groups. In conclusion, the study demonstrated that oyster mushroom powder as a prebiotic significantly mitigated tissue damage in Nile tilapia exposed to silver sulfate and enhanced immune responses, marking it as a promising dietary supplement in aquaculture.</p>