Sublethal Triclosan triggers oxidative stress and autophagy responses in Labeo rohita

Triclosan (TCS), an antimicrobial agent widely incorporated in personal care products, has become a persistent aquatic contaminant, posing potential risks to freshwater organisms. This study examined sub-lethal TCS toxicity in Labeo rohita, demonstrating its capacity to disrupt oxidative balance, hematology, antioxidant defenses, and induce multi-organ damage. Fish were exposed for 6 weeks to two concentrations of TCS: 0.0742 mg/L (T1) and 0.148 mg/L (T2), representing one-tenth and one-fifth of the 96-h LC₅₀, respectively, under semi-static conditions. At each sampling interval, one fish from each replicate tank was sampled for biochemical, histopathological, and qRT-PCR analyses (n = 3 biological replicates per treatment group). TCS exposure induced significant (p < 0.05), dose- and time-dependent oxidative stress, evidenced by increased reactive oxygen species (ROS), reduced hemoglobin (Hb) and red blood cells (RBCs), and elevated white blood cells (WBCs). Antioxidant responses showed increased superoxide dismutase (SOD), catalase (CAT), and lipid peroxidation (LPO) and decreased reduced glutathione (GSH), following the organ-specific severity order: gill > kidney > muscle. Gene expression analysis via qRT-PCR indicated a clear shift in autophagy-related markers, showing elevated levels of atg5, beclin1, lc3, and ulk1b, along with reduced mTOR expression, suggesting enhanced autophagic activity under TCS-induced oxidative stress. The response displayed tissue-specific variation, with gill showing the greatest sensitivity, followed by kidney and muscle. Histopathological damage increased dose-dependently: T1 showed mild gill, kidney, and muscle lesions, whereas T2 exhibited severe gill oedema and aneurysm, marked renal degeneration, and extensive muscle fiber disruption. Pearson correlation analysis showed strong links among oxidative stress, hematological alterations, antioxidant responses, and alterations in gene expression. Altogether, TCS induced clear dose-dependent toxicity in L. rohita, highlighting its significant chronic ecological risk to freshwater systems even at low concentrations.