There is a general consensus among scientists that climate change poses a severe threat to organisms with little tolerance for higher temperatures than those in their current environmental niche. The effects of increased environmental temperature will be of significance in those organisms combining reduced thermal tolerance and limited mobility across the environment to allow shifts to more optimal habitat. The relict populations of the freshwater crayfish genus, Euastacus, in Queensland are generally restricted to cooler mountain-top streams and are at significant extinction risk due to these factors. While noted as threatened by increases in environmental temperature, key knowledge gaps exist regarding the thermal biology of these crayfish. This project sought to answer the underlying question; Are species of Euastacus in Queensland, some with severely restricted distributions, currently experiencing thermal stress in warmer parts of the year? It was anticipated that evidence of fitness reducing temperatures in these crayfish would give an indication of the future effect of climate change, primarily increased temperature, and initiate further research into this vulnerable genus. A minimally-intrusive assessment of physiological and biochemical indicators of tissue damage in response to an imposed thermal stressor were initially developed using a model organism, Cherax quadricarinatus. The data provided “proof of concept” for a validated method to contrast the level of thermal stress experienced between individuals of the same species, conditioned to different temperatures. Additionally, the results indicated that the physiological and biochemical indicators gave some defined effects of higher temperature on the model organism, and opened up the potential for a suite of non invasive assays to be used within the genus Euastacus.