This course aims to outline the differences in key mechanisms associated with physiological performance in fishes, specifically oxygen uptake, transport, and delivery. Comparisons are made to other vertebrates, namely humans. Key disturbances for marine fishes -- such as ocean warming, ocean acidification, and declining water quality, specifically sedimentation -- are discussed, especially in terms of how these stressors affect fish performance. Results and conclusions from these types of studies have implications toward population stability, maintaining biodiversity, biogeography of species, and potential for acclimation and adaptation to changing oceans.