The physiological activities of fish determine the range of energy required during metabolic processes, especially in osmoregulation during the fish's adaptation period to saline environment. This research aimed to determine the effect of salinity on the physiological performance of the Asian redtail catfish (Hemibagrus nemurus). The results obtained showed that the physiological performance of fish against media changes in the form of increasing salinity. The research was conducted for 30 days from June to July 2022 at the Cultivation Technology Laboratory, University of Riau, Indonesia. The juveniles used were 7-8cm in size, as many as 200 individuals, using different salinity treatment levels of 3, 6, 9, 12, and 15ppt with 4 replications. The research results showed that the best physiological performance of the Asian redtail catfish was found at the salinity of , with a cortisol level of 12.56mg mL^–1 and an oxygen consumption level of 0.9mg O₂ g^–1 hour^-–1.  Meanwhile, the optimal plasma and media osmolarity was observed at a salinity of 9ppt, which was also associated with the lowest levels of cortisol and oxygen consumption.