Silica nanoparticles are novel aqueous additive mitigating heavy metals toxicity and improving the health of African catfish, Clarias gariepinus

•Silica nanoparticles (SiNPs) aqueous suspension alleviates the toxic effect of heavy metals (HMs) toxicity in C. gariepinus.•The exposed fish to Hg and Pb ions reveals microcytic hypochromic anaemia and down-regulation of genes.•Exposure to HMs reduces some immune-antioxidant and hepato-renal indicators as well as histological changes.•Exposure to SiNPs improves hemato-biochemical biomarkers and regenerates the histological alterations.•SiNPs decreases the accumulation of HMs ions in fish muscles.