Temperature plays a key role in the physiology of aquatic ectotherms. Northern Crayfish (Faxonius virilis) are a keystone freshwater macroinvertebrate found in North America from Oklahoma to Manitoba and therefore are subjected to a wide variety of water temperatures. The current study investigates the thermal physiology of F. virilis across a wide range of temperatures between 5C to 25C for 14 days and to acute heat stress. The animals’ routine and maximum oxygen consumption (MO2) and associated hemolymph acid-base parameters were assessed. Additionally, MO2 and metabolically produced ammonia was measured in isolated gill tissue. Warmer temperatures resulted in predictable increases in the animal’s ammonia excretion rates and MO2. Notably, the isolated gill tissue of F. virilis had 4-14 times higher rates of oxygen consumption compared to the whole animal, signifying its importance for respiration. Hemolymph measurements resulted in a significant pH and [HCO3-] decrease at higher temperatures, suggesting a metabolic acidosis. Acute exposure to a +5C increase relative to baseline conditions caused a significant increase in ammonia excretion rates and MO2 in both the whole animal and isolated gill tissue. Crayfish acclimated to 5C resulted in drastically different physiological outcomes compared to warmer acclimated crayfish, signifying a reduced metabolic state. Overall, F. virilis is capable of rapid adjustments to oxygen consumption, excretion, and associated hemolymph parameters needed to respond to heat stress of +5C for 6 hours, and demonstrates a high degree of plasticity to temperatures between 5C and 25C.