Understanding how environmental conditions mediate the performance of individuals represents an important step towards predicting how environmental perturbations may impact populations. Rainfall reductions, along with increased development, are changing environmental conditions in south-west Australia’s iconic Swan-Canning Estuary. Of particular concern are protracted periods of hypoxia that may impact recreational and commercial fish stocks. Here, we quantified the metabolic physiology, via respirometry, and the voluntary activity, via animal-attached accelerometers, of Black Bream (Acanthopagrus butcheri), a southern Australian estuarine specialist, across a range of ecologically-relevant temperatures and dissolved-oxygen saturations. Our results show that Black Bream display temperature-dependent metabolic physiology, sensitive to changes in oxygen saturation, that translate into changes in voluntary activity under field conditions. Overall, our data will be useful in quantifying how past and future changes in environmental conditions impact this iconic estuarine species.