Ichthyophthirius multifiliis (I. multifiliis) is a parasite that poses a serious hazard to global freshwater aquaculture. This study investigates the efficacy of biologically synthesized chitosan nanoparticles (ChNPs) as a sustainable antiparasitic alternative for controlling I. multifiliis in Nile tilapia. Thus, a total of 400 mono-sex Nile tilapia fingerlings were randomly distributed into 40 glass aquaria (eight groups, five replicates, 10 fish each). The groups included: control, T1–T3 (ChNPs at 80, 160, and 320 mg/kg), T4 (praziquantel-treated), T5 (I. multifiliis-infected), T6 (I. multifiliis + ChNPs, 320 µg/kg), and T7 (I. multifiliis + praziquantel, 320 µg/kg). ChNPs characterization showed a UV peak at 220 nm, a spherical shape in TEM, and an exact size of 80 nm in DLS. ChNPs (320 µg/mL) and showed strong antioxidant activity, scavenged 88% of DPPH, and showed 90% inhibition of I. multifiliis trophonts via direct lysis, as confirmed by TEM. In vivo, dietary ChNPs (320 μg/kg) enhanced growth performance, increasing final body weight by 29 % and improving FCR (4.0 vs. 4.9). Infected fish treated with ChNPs showed full survival (100 vs. 88.7% in untreated), reduced cortisol levels by 76%, and restored liver function, where reducing the ALT by 50 % compared to infected untreated fish. ChNPs modulated immune reaction, enhancing NBT activity (0.87 vs. 0.41 in controls) and upregulating immune genes [Interleukin-8 (CXCL8) and Type II interferons (IFNϒ)] in healthy fish, while suppressing hyperinflammation in infected fish. Histopathological examinations showed that ChNPs effectively reversed gill damage by significantly reducing hyperplasia and lowering trophont burden, revealing a therapeutic impact contrasted to that of praziquantel. It could be concluded that ChNPs has a dual-action therapeutic, directly targeting I. multifiliis and enhancing host health via immunomodulation and growth promotion. The efficacy, safety, and sustainability of ChNPs make them potent alternatives to chemical parasiticides in aquaculture.

To Cite This Article: Alsulami MN, 2025. The efficacy of biogenic chitosan nanoparticles in controlling Ichthyophthirius multifiliis infection in Nile Tilapia (Oreochromis niloticus). Pak Vet J. http://dx.doi.org/10.29261/pakvetj/2025.308