African catfish (Clarias gariepinus) acquires elevated interests with their nutritional importance and propagation easiness, but maintaining their products' quality is challenging. The extract of Salvia officinalis petals (SO) was employed for mediating selenium nanoparticles (SeNPs), using direct and facile procedure. Chitosan nanoparticles (CTn) were composited with SO/SeNPs and their nanocomposites (NCs) and parent materials were characterized using spectroscopy and electron microscopy. The SO, with its phenolic contents, effectively mediated SeNPs that had 13.48 nm mean size. The CTn-SO/SeNPs nanoconjugation was achieved and validated using infrared (FTIR) analysis and scanning microscopy. The biopreservation of catfish fillets using fabricated nanomaterials/NCs was very promising, during storage of coated samples for 25 days. The most auspicious treatments were the coating with 0.5% solution of SO/SeNPs and CTn-SO/SeNPs, respectively, for maintaining the fillets' sensory attributes (acceptability, color, odor, flavor and texture) throughout storage. The fillets' coating with NCs could significantly reduce the progress of spoilage parameter (pH, volatile basic nitrogen; TVB-N and reactive thiobarbituric acid; TBARS), compared with control. The SO-mediated SeNPs and their nanoconjugates with CTn provided effectual bases for edible coating to preserve catfish fillets and maintain their quality.