Since 2000, global mean annual temperatures have risen by 0.750C and the Southern Plains region in north Texas has experienced record-breaking drought events. Intense drought exposes fishes to extreme water temperatures and hypoxic conditions, especially when streams are fragmented into isolated pools. Given that both the frequency and intensity of drought events is expected to continue to increase, futures for freshwater fishes are uncertain. One important unknown is the extent to which adaptive capacity may enable evolutionary rescue in fish populations impacted by increasingly extreme droughts. For four imperiled fish species, we have the unique opportunity to assess adaptive responses to changing environmental conditions over the past quarter century by comparing results from contemporary research to those from research conducted on the same populations 25 years ago. In this study, we quantified thermal and hypoxia tolerance for four imperiled fish species native to the Upper Brazos River – federally endangered Sharpnose Shiner (Notropis buccula), federally endangered Smalleye Shiner (Notropis oxyrhynchus), state threatened Red River Pupfish (Cyprinodon rubrofluviatilis) and state SGCN Plains Minnow (Hybognathus placitus). Thermal tolerance (CTmax) and hypoxia tolerance (hypoxia LOE and Pcrit) metrics were quantified for 36 individuals of each species to determine underlying systemic stress responses. Sequential CTmax experiments were conducted using two heating rates: 0.30C/min to align with current convention, and 0.50C/min to allow for direct comparisons to prior research. A Loligo 4 chamber static respirometry system was used for hypoxia tolerance testing. We assessed interspecific and intraspecific variation among individual results for CTmax, Pcrit, and hypoxia LOE using mixed models, and compared our species-level results to those of Ostrand and Wilde (2001) using t-tests. Our study provides novel information regarding the potential for evolutionary rescue in these four imperiled species and can be used to inform conservation planning and management actions.