Globally, freshwater fish numbers have declined substantially in part due to anthropogenic structures (e.g. dams) that impede fish movements. The environmental and societal benefits of balancing environmental health with human resource requirements have meant that there is increasingly a concerted effort to remove or remediate barriers to fish passage. However, this is technically, financially, and biologically challenging. Experimental approaches provide a controlled, iterative, integrative, and cost-effective approach to assess the physical, physiological, and behavioural limitations of fish that can be used to provide evidence-backed information to support or develop remediation practices. This chapter explores some of the physiological tools used to measure fish performance in modified environments, and how empirical studies are informing current issues in the management of freshwater fish passage.