Elevated carbon dioxide has limited acute effects on Lepomis macrochirus behaviour

The current study investigated the behavioural response of Lepomis macrochirus following exposures to elevated carbon dioxide (CO₂ ). For this, L. macrochirus were held at ambient pCO₂ (160 μatm pCO₂ ) for 7 days, then exposed to elevated pCO₂ (8300 μatm pCO₂ ) for 5 days, and then returned to ambient conditions for a further 5 days to recover. At the end of each exposure period, several behavioural metrics were quantified (boldness, lateralization and activity). Data showed no change in lateralization and most metrics associated with performance and boldness. During the boldness test, however, average velocity, velocity in the thigmotaxis (outer) zone and proportion of activity in the thigmotaxis zone increased with pCO₂ exposure. During post-exposure, average velocity of L. macrochirus decreased. In addition, individual rank was repeatable during the pre-exposure and post-exposure period in three of the 17 metrics investigated (average velocity in the middle zone, average velocity near object and total shuttles to the object zone), but not during the CO₂ exposure period, suggesting that elevated pCO₂ disrupted some behavioural performances. Overall, this study found elevated pCO₂ caused disruption to behaviours of freshwater fishes such as L. macrochirus and effects do not appear to be as serious as has been shown for marine fishes.