There is strong relation between nutrition and thermal tolerance of fish in terms of improved critical temperature minima (CTmin), lethal temperature minima (LTmin), critical temperature maxima (CTmax), and lethal temperature maxima (LTmax). Fishes act as quantifying indicators of the climate change due to their critical thermal limits in nature and ability to adjust thermal sensitivity to maintain their homeostasis. In the present study, biologically synthesised selenium nanoparticles (Se-NPs) from fisheries waste (fish gill) were used to evaluate its efficacy for enhancement of thermal tolerance of Pangasius hypophthalmus reared under lead (Pb) and high temperature (34°C) for 72days. At the end of the experimental period, CTmin, LTmin, and CTmax, LTmax and cellular metabolic stress were evaluated. The CTmin, LTmin were noticeably (p<0.01) reduced and CTmax, LTmax were enhanced in treatment groups fed with dietary Se-NPs. It was also observed that CTmax and LTmax were increased with acclimation temperature. The positive correlation was perceived between CTmin, LTmin (Y=-0.45+11.05x, R, 0.768) and CTmax, LTmax (Y=-0.78+8.17x, R, 0.858) fed with Se-NPs supplemented diet and exposed to Pb and high temperature. Significant improvements in the oxidative and metabolic enzymes were noticed post thermal tolerance experiment. Overall results indicated that incorporation of Se-NPs @ 1mg/kg in diet can confer protection against Pb and thermal stress in P. hypophthalmus.