Abstract
The present experimental study was conducted to evaluate the acute toxicity of green-synthesized zinc oxide nanoparticles (G-ZnO NPs) in a commercially important marine fish species, silver pompano (Trachinotus blochii). The nanoparticles were synthesized using guava (Psidium guajava) leaves extract and zinc nitrate hexahydrate as the precursor. The synthesized G-ZnO NPs exhibited a characteristic UV-Visible absorption peak at 335 nm, confirming the formation of ZnO nanoparticles. XRD analysis revealed distinct diffraction peaks corresponding to the hexagonal wurtzite crystalline structure of ZnO, with an average crystallite size of 24.4 nm. FTIR analysis showed ZnO stretching vibrations at 531 cm⁻1 and 485 cm⁻1 along with functional groups involved in nanoparticle capping and stabilization. FESEM analysis demonstrated predominantly spherical and well-dispersed nanoparticles with an average particle size of 32.4 nm, while TEM analysis revealed monodispersed and less agglomerated spherical nanoparticles ranging from 32 to 49 nm with an average size of 39.6 nm. EDS analysis confirmed the elemental composition of Zn (70.37%), O (20.64%), and C (8.99%). The zeta potential value of -30.5 mV indicated good colloidal stability of the synthesized nanoparticles. Silver pompano (17.5 ± 2 cm) were exposed to six concentrations (0, 20, 40, 60, 80, and 100 mg/L) for 96 h to determine acute toxicity and associated physiological responses. The 96 h median lethal concentration (LC50) was found to be 90.45 mg/L. Significant alterations (p < 0.05) were observed in hematological parameters, including red blood cell (RBC), white blood cell (WBC), lymphocytes, hemoglobin (Hb), hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC) and platelet count, as well as antioxidant enzymes such as catalase (CAT), myeloperoxidase (MPO), and superoxide dismutase (SOD) across all concentrations. Notably, red blood cell count and hemoglobin levels increased at 60 mg/L, whereas platelet count decreased significantly at all concentrations. Respiratory burst activity showed a slight increase at 100 mg/L. Histopathological analysis revealed fatty vacuolation, mononuclear cell infiltration, and congestion in liver tissues at higher concentrations (80 and 100 mg/L), while gill tissues exhibited lamellar fusion and severe aneurysm at 100 mg/L. In conclusion, G-ZnO NPs exhibited relatively low toxicity at sub-lethal concentrations (20, 40 and 60 mg/L) and may offer potential applications in aquaculture and fish disease management.