Bowman et al. CO2 data

A two-part experiment was conducted to determine whether visual indicators of consciousness, including equilibrium, eye-roll reflex, and ventilation, were accurate measures for consciousness during CO2 stunning of rainbow trout (Oncorhynchus mykiss Walbaum, 1972). Part 1 monitored time to loss of visual indicators in rainbow trout during CO2 stunning under field conditions at 14°C, 8°C, and 2°C. Analysis showed that time to loss of visual indicators increased as temperature decreased, with significant differences in time to loss of equilibrium between 2°C and 14°C, and significant differences between all temperatures in time to loss of eye-roll reflex and ventilation. In part 2 trout were equipped with external non-invasive electrodes for measurement of EEG and exposed to repetitive light stimulation to evoke responses (VERs) indicative of brain function. This was done before and after exposure to CO2 saturated water in a laboratory environment at 10°C. EEG recordings showed a poor relationship between visual indicators of consciousness and loss of brain function, with VERs continuing up to 3.5 min after ventilation was lost and up to 6.5 min after the fish lost equilibrium. Together, these results show that cold-water temperatures prolong time to loss of consciousness and that visual indicators are insufficient when determining when consciousness is lost in rainbow trout during CO2 stunning.