Dietary lemon essential oil mitigates metalaxyl-induced oxidative stress, hematological disruptions, and immunotoxicity in Nile tilapia (Oreochromis niloticus) with associated changes in splenic MAPK-and caspase-related gene expression.

The agricultural accumulation of the phenylamide fungicide metalaxyl (MXL) poses an increasing threat to aquatic organisms. Natural compounds, such as Citrus limon peel essential oil (CLPO), offer antioxidant and immunostimulant properties that may counteract these toxic effects. This study evaluated the protective effects of a CLPO-enriched diet against MXL-induced toxicity in Oreochromis niloticus. For 12 weeks, fingerlings (33.46 ± 0.28 g; n = 50 per group) were assigned to four treatments: Control, CLPO (1 g/kg diet), MXL (12.34 mg/L), and CLPO+MXL. MXL exposure reduced survival to 78%, disrupted hematological parameters (decreased white and red blood cells, hemoglobin, and hematocrit), and elevated glucose and cortisol levels. Immune dysfunction was evidenced by reductions in complement 3, lysozyme, nitric oxide, and myeloperoxidase. Furthermore, MXL triggered oxidative stress, marked by diminished antioxidant enzyme activities and increased malondialdehyde levels. At the molecular level, MXL exposure upregulated the stress-signaling transcripts (mapk1 and mapk14) and pro-apoptotic genes (casp-3 and casp-8), while concurrently suppressing the anti-inflammatory cytokine il-10. These physiological changes correlated with splenic depletion and enlarged melanomacrophage centers. Conversely, dietary CLPO enhanced immune-antioxidant function, restored hematological profiles, mitigated gene expression disturbances, and preserved splenic structure. Overall, dietary CLPO supplementation significantly attenuated several adverse effects under the present experimental conditions, highlighting its potential as a protective additive in aquafeeds.