Wildfires can have significant but often overlooked impacts on aquatic ecosystems, particularly when rainfall after fire transports ash, sediment, and dissolved materials into rivers and estuaries. These post-fire runoff events can rapidly alter water quality and expose aquatic organisms to stress, yet the early behavioural and physiological responses of aquatic invertebrates remain poorly understood. This study investigated how whole wildfire ash affects the South-west glass shrimp (Palaemon australis), a small, abundant crustacean endemic to Western Australia. The glass shrimp is an ecologically important detritivore and a key prey item for native fishes, contributing to nutrient cycling and energy transfer within aquatic food webs while serving as a potential early indicator of environmental disturbance. Using controlled laboratory experiments, shrimp were exposed to environmentally relevant ash concentrations while behavioural responses, including aquatic surface respiration, activity, and refuge use, were quantified alongside routine metabolic rate measured using intermittent aquatic respirometry. Following exposure, shrimp were transferred to ash-free water to assess recovery and determine whether responses are temporary or persistent beyond the initial disturbance. Comparing responses across ash concentrations and recovery periods identified thresholds at which wildfire ash begins to elicit measurable physiological and behavioural stress. By identifying early-warning indicators of stress and the capacity for recovery following ash exposure, this research provides new insight into the resilience of aquatic invertebrates to post-fire runoff. These findings improve understanding of how wildfire ash may affect nutrient cycling, prey availability for native fishes, and the resilience of aquatic food webs, supporting the monitoring and management of fire-affected waterways.