Dietary thyme essential oil (Thymus vulgaris) changes serum stress markers, enzyme activity, and hematological parameters in gibel carp (Carassius auratus gibelio) exposed to silver nanoparticles

Gibel carp (Carassius auratus gibelio) juveniles with an average weight of 8.73± 2.1 g were fed a basal diet (control) and three experimental diets (T200, T400 and T800), containing 200, 400 and 800 mgkg-1, respectively of thyme essential oil (Thymus vulgaris) for six weeks. After six weeks feeding trial, both control and thyme essential oil-added feed groups were exposed to sub-acute toxicity of silver nanoparticles (Ag-NPs) for a period of 96 h. At 96 h after exposure, the number of erythrocytes (RBC), leucocyte (WBC), hematocrit (Hct), hemoglobin (Hb), the differential leukocyte count in blood and alanine aminotransferase (ALT), aspartate aminotransferase (AST) activity, HDL-cholesterol, LDL-cholesterol, cortisol and lactate in serum were measured. The results revealed feeding a thyme essential oil diet significantly conferred resistance to oxidative stress with sub-acute toxicity of Ag-NPs. Thyme essential oil enhanced the RBC and WBC count, hematocrit and hemoglobin content, at both low (T400) and high doses (T800). Biochemical analysis showed that serum ALT and AST activities, and LDL-cholesterol in the thyme essential oil-added feed groups were significantly reduced with increasing dietary thyme essential oil. Plasma HDL-cholesterol was significantly elevated by a high-dose of dietary thyme essential oil (T800). Furthermore, cortisol and lactate levels in serum significantly decreased throughout the thyme essential oil-added feed groups compared to the control. In summary, the use of thyme essential oil at 400 and 800 mgkg-1, as dietary supplements, has potential to decrease oxidative stress of gibel carp providing resistance to non-fatal effects of pollutant by Ag-NPs.