Assessing the impact of dietary selenium administration on trichlorfon-induced toxicity in Nile tilapia (Oreochromis niloticus) reared in a laboratory-based setup.

The safety of aquatic systems has been threatened by the extensive and inappropriate application of trichlorfon pesticides. Thus, five groups of 60 tilapia each, in three replicates, were randomly selected from 300 fingerlings of Oreochromis niloticus (15.63 ± 0.05 g, SE). The first group was fed a basic diet and raised in clean water. The remaining fish were grouped into four groups, reared in water polluted with partially lethal trichlorfon concentration (0.38 mg/l), and fed with formulated diets consisting of trichlorfon (control diet), Se-Cys (selenium cysteine), nano-Se (Se nanoparticle), and Se-Met (Se-methionine) added at 1 mg/kg diet each for 90 days, followed by challenge with A. hydrophila. Enhanced growth, improved hematological profile (RBCs, WBCs, Hb, PCV) and minimum serum stress (ALT, AST, glucose, triglyceride, cholesterol) with elevated immunological indices (NBT, lysozyme, myeloperoxidase, albumin, globulin, total protein) were performed by nano-Se supplemented group. Additionally, antioxidant enzyme assays and oxidative stress gene expression (CAT, SOD, GPx, and GST) were effectively augmented by the same group in the sampled tissues. Nano-Se group was noticed by upregulated immune-related selenoproteins (Sepp1a, SelK, GPx2, and SelW) in gill and liver tissues. In contrast, immune stress genes (CASP3, HSP70, TNF-α, and IL-β) were upregulated in the trichlorfon group. Stress hormone biomarkers (cortisol, GH, TSH, T3, T4) and intestinal enzymes (protease, lipase, and amylase) were effectively achieved by the Se-incorporated groups. All Se sources exhibited minimum cumulative mortality compared to the control in response to A. hydrophila. Liver tissues exhibited the maximum Se bioaccumulation and Se concentration factor among all the sampled tissues. This is the first report that we are aware of examining the comparative effects of Se sources on trichlorfon stress in fish models. It could be concluded that supplementation with different forms of Se, mainly nano-Se, successfully ameliorated the toxic effects of trichlorfon in tilapia.