The fear, flight or fight response serves as the fundamental physiological basis 
for examining an organism's awareness of its environment under an impending 
predator attack. Although it is not known whether invertebrates possess an 
autonomic nervous system identical to that of vertebrates, evidence shows 
invertebrates have a sympathetic-like response to regulate the internal 
environment and ready the organism to act behaviorally to a given stimuli. 
Furthermore, this physiological response can be feasibly measured and it acts as 
a biological index for the animal's internal state. Measurements of the 
physiological response can be directly related to internal and external 
stressors through changes in the central nervous system controlled coordination 
of the cardio-vascular and respiratory systems. More specifically, monitoring 
heart and ventilation rates provide quantifiable measures of the stress response 
not always behaviorally observed. Crayfish are good model organisms for heart 
and ventilatory rate measurements due to the feasibility of recording, as well 
as the rich history known of the morphology of the crayfish, dating back to 
Huxley in 1888, and the well-studied typical behaviors.