Given its superior bioactivities and biocompatibility, chitosan (CS), a natural polymer that is biodegradable and nontoxic, is widely used in food and biomedical industries. The presence of anionic elements is required to achieve the superior gelling characteristic of CS, which is attributable to its polycationic nature. Additionally, compared to the free form, the chitosan nanoparticles (CSNPs) enhanced bioactivities, such as antioxidant and antibacterial activities and improved stability during storage and continuous release. This study attempted to explore the main uses of CSNPs as a fish preservation agent for Sardinella aurita. Antimicrobial activities of CS and CSNPs were tested against S. aureus and E. coli. Moreover, CS and CSNPs were sprayed over two fish groups, with a third group left untreated (control group). Results delineated the significant antibacterial potential of CSNP compared to CS and control (Gentamycin). Additionally, compared to the CS and control groups, the fish exposed to CSNPs had higher organoleptic indices in their eyes, gills, mucus, flesh, texture, and smell. Conclusively, the spray made from shrimp shell waste as CSNPs has good antibacterial and preservation properties. When processing or transporting fisheries products, CSNPs might work as an antibacterial agent and a natural preservative.