Silver nanoparticle toxicity in rainbow trout: insights into physiological and molecular responses

Metallic nanoparticles, with their large surface area to volume ratio, are increasingly important in various life fields, but they can cause varying toxic effects on fish. This study investigates the toxicological effects of silver nanoparticles (AgNPs) on rainbow trout (Oncorhynchus mykiss), focusing on hematological, biochemical, antioxidant, and histopathological changes. Fish were exposed to varying concentrations of AgNPs (0.2, 0.8, and 1.4 mg/L) for 21 days. Hematological analysis revealed significant reductions in red blood cell (RBC) counts, hemoglobin (Hb), and hematocrit (HCT) at higher AgNPs concentrations, while white blood cell (WBC) counts increased, indicating immune system activation. Biochemical assays demonstrated dose-dependent decreases in total protein and albumin, alongside increased cholesterol and triglyceride levels, suggesting impaired liver function and disrupted lipid metabolism. Antioxidant enzyme activity (SOD, CAT, GST) initially increased at lower AgNPs concentrations but declined at higher exposures, indicating oxidative stress. Molecular analysis further supported these findings, with upregulation of oxidative stress-related genes (SOD1, CAT) and inflammatory markers (HSP70, IL-1β). Histopathological examinations revealed necrosis, hyperplasia, and lamellar fusion in the gills, along with significant liver damage, including vacuolation and Kupffer cell proliferation, particularly at the highest exposure. Behavioral assays showed erratic swimming and reduced feeding in fish exposed to higher AgNPs concentrations. This study highlights the dose-dependent toxic effects of AgNPs on rainbow trout and underscores the potential for long-term, possibly irreversible damage at higher exposure levels. These findings emphasize the need for stricter environmental regulations on nanoparticle use to mitigate their ecological impact.