A 70-day feeding trial was conducted to evaluate the effects of dietary supplementation of selenium nanoparticles (Se-NPs) on physiological and biochemical aspects of juvenile mahseer (Tor putitora) fish. Maintaining a 40% protein level, 2 different experimental diets supplemented with 0% Se-NPs and 0.68 Se-NPs mg kg-1 were fed to triplicate groups of fish. The experiment was conducted in a semistatic condition consisting of 6 fiber tanks. The fish were first acclimatized, and then 30 fish per tank were randomly put into each fiber tank. At the end of the feeding trial, samples were collected from the fish and analyzed. Results obtained showed that the diet supplemented with Se-NPs significantly increased (P < 0.05) physiological aspects like red blood cell count, hemoglobin level, hematocrit values, and lysozyme activity as compared to the basal diet. Similarly, biochemical parameters including serum growth hormone levels, tissue total protein content, and glutathione peroxidase activity in liver and muscle tissues of T. putitora also significantly (P < 0.05) increased. Thus, dietary Se-NP supplementation at the rate of 0.68 mg kg-1 diet has very beneficial effects on the physiobiochemical health aspects of juvenile T. putitora.