Nrf2-Linked Antioxidant and Metabolic Modulation by Dietary Origanum vulgare Essential Oil in Nile Tilapia Under Organophosphate Stress

Phytobiotics are promising dietary tools to improve metabolic stability and physiological resilience against chemical stressors in aquaculture. This study evaluated nrf2-linked antioxidant and metabolic modulation by dietary Origanum vulgare essential oil (OEO) in Nile tilapia (Oreochromis niloticus) under malathion-induced organophosphate stress. Fish, with an initial weight of 5.76 ± 0.56 g, were distributed in three tanks per treatment, with 15 fish per tank, and fed diets containing 0 (control), 0.75, 1.50, 2.25 and 3.00 g kg−1 OEO for eight weeks, followed by exposure to malathion (7.04 mg L−1) for 96 h. OEO enhanced (p < 0.05) growth performance, feed utilisation, and survival after exposure, with the greatest productive and survival outcomes at 3.00 g kg−1. Fish that received the supplement also had lower (p < 0.05) lipid peroxidation, better antioxidant enzyme activity and a more favourable modulation of nrf2, gpx and keap1 expression, together with biochemical and histological patterns that were consistent with a better condition of the liver and kidney. The heatmap and PCA supported a treatment-related separation, with 2.25 and 3.00 g kg−1 OEO showing the most favourable integrated physiological profiles. Dietary OEO was associated with antioxidant, metabolic and tissue-level resilience linked to modulation of nrf2-related transcriptional responses.