Climate change and pollution are the major contributors to the aquatic system degradation. These factors also affect the existence and suitability of the aquatic animals. These abiotic factors affect the thermal tolerance of the Pangasianodon hypophthalmus. In the above backdrop, an experiment was conducted to delineate the role of nano‑copper (Cu-NPs) in the enhancement of thermal efficiency, anti-oxidative gene expression, and immunity of the P. hypophthalmus reared under arsenic (As), high temperature (34 °C) and low pH (6.5) stress for 110 days. Four isocaloric and isonitrogenous diets containing Cu-NPs at 0, 1.0, 1.5, and 2.0 mg kg−1 were formulated and prepared. The thermal efficiency study was conducted at the end of 110 days feeding trial and determined the critical thermal minima (CTmin), lethal thermal maxima (LTmax) and lethal thermal minima (LTmin), and critical thermal maxima (CTmax). The cortisol, heat shock protein (HSP 70) gene, and neurotransmitter enzymes were noticeably affected by As, As+T and As+pH+T, whereas it improved by dietary Cu-NPs during LTmin and LTmax. The genes related to immunological index viz. tumor necrosis factor (TNFα), interleukin (IL1b), inducible nitric oxide synthase (iNOS), immunoglobulin (Ig) and toll like receptor (TLR) in liver were noticeably altered with stressors. Whereas dietary Cu-NPs at 1.5 mg kg−1 diet improved the immune systems by improving gene expression during LTmin and LTmax. The anti-oxidative related gene expression SOD, CAT, and GPx were significantly enhanced with As, As+T, and As+pH+T, whereas Cu-NPs remarkably reduced the oxidative stress. The bioaccumulation and concentration of arsenic in P. hypophthalmus muscle and water were significantly reduced using dietary Cu-NPs. It also protects the tissues against DNA damage during LTmax. The present investigation revealed that supplementation of Cu-NPs at 1.5 mg kg-1 diet improves thermal efficiency and gene regulation related to anti-oxidative and immunity of the P. hypophthalmus.