Molecular and behavioral responses of early-life stage fishes to elevated carbon dioxide

Bigheaded carps are non-native invasive fishes that have quickly become the most abundant fishes in many portions of the Midwestern United States. While the spread of bigheaded carps into the Great Lakes is currently impeded by three electrified barriers, these fish have the potential to negatively impact the Great Lakes ecosystem if this barrier is breached, and these barriers may be particularly vulnerable to the passage of small fishes. As such, novel barrier technologies would provide an additional mechanism to prevent bigheaded carps from invading the Great Lakes, and provide much needed redundancy to the current electric barrier. The current study used a combination of molecular and behavioral experiments to determine the effectiveness of carbon dioxide as a chemical deterrent for larval and juvenile fishes, with an emphasis on bigheaded carps. Juvenile silver carp (Hypophthalmichthys molitrix), bighead carp (H. nobilis), bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides) showed avoidance of elevated CO₂ environments at approximately 200 mg/L. Additionally, exposure to 120 mg/L CO₂ resulted in the induction of hsp70 mRNA in 8 days old silver carp fry, while gill c-fos transcripts increased following hypercarbia exposure in all juvenile species examined. Together, our results show that CO₂ has potential to deter the movement of larval and juvenile fishes.