Temperature dependent effects of carbon dioxide on avoidance behaviors in bigheaded carps

Effective behavioral deterrents are needed to prevent aquatic invasive species from entering novel ecosystems. One deterrent strategy that shows promise is elevated carbon dioxide (CO2) concentrations in water which can alter the behavior of freshwater fishes, including invasive bigheaded carps (Hypophthalmichthys spp.). However, few studies have evaluated behavioral responses to elevated CO2 concentrations at different water temperatures. The objective of this study was to quantify CO2 concentrations needed to achieve avoidance (voluntary response) and narcosis (involuntary response observed by loss of equilibrium) behaviors in silver carp (H. molitrix) and bighead carp (H. nobilis) at 5, 15, and 25 degrees C. Overall, silver carp and bighead carp displayed avoidance and narcosis behaviors to CO2 at each water temperature, however bighead carp responded at higher CO2 concentrations than silver carp. Behavioral avoidance and narcosis were observed at approximately 40% lower CO2 concentrations in 5 degrees C water relative to 25 degrees C suggesting considerable influence of water temperature on a CO2 stimulus for both species. Results indicate that fluctuating water temperature (e.g., spatial and temporal variation across management sites) can influence how fish respond to elevated CO2, and may usefully be considered when applying CO2 as a behavioral deterrent.