Dietary Probiotics Modulate Oxidative Stress, Metabolic Status, and Immune-Related Gene Expression in Nile Tilapia (Oreochromis niloticus) Exposed to Malathion

Malathion, a widely used organophosphate pesticide, frequently contaminates aquatic ecosystems and poses considerable toxic risks to non-target organisms, including fish. The present study provides an integrated evaluation of the protective effects of dietary probiotics against malathion-associated oxidative, metabolic, and immune-related disturbances in Nile tilapia at the biochemical and molecular levels. After determining the 96 h LC50 of malathion, fish were exposed to a sublethal concentration for 7 days followed by a 14-day recovery period while receiving either a basal or probiotic-supplemented diet. Malathion exposure increased cumulative mortality, induced behavioral stress, and caused metabolic and hepatorenal disturbances characterized by elevated serum glucose and cholesterol, altered serum protein fractions, increased alanine and aspartate aminotransferase activities, and elevated creatinine and uric acid levels. Oxidative stress was evidenced by increased serum malondialdehyde and transcriptional suppression of antioxidant-related genes (sod-2 and cat) in the liver, spleen, and intestine. Malathion also triggered immune dysregulation through the upregulation of pro-inflammatory cytokine genes (il-1β and tnf-α) and suppression of regulatory cytokines (tgf-β and il-10). Probiotic supplementation during recovery significantly reduced mortality, restored metabolic and hepatorenal biomarkers, attenuated oxidative damage, and enhanced antioxidant capacity at both the biochemical and transcriptional levels. Moreover, probiotic-supplemented fish exhibited controlled pro-inflammatory signaling accompanied by the pronounced activation of regulatory cytokines, indicating balanced immune modulation. Collectively, dietary probiotics effectively mitigate malathion-induced toxicity by improving antioxidant defense, immune regulation, and physiological resilience, highlighting their potential as functional dietary additives for sustainable aquaculture in Nile tilapia.