Exposure to elevated pCO₂ alters post-treatment diel movement patterns of largemouth bass over short time scales

Studies with marine fishes indicate that exposure to elevated partial pressures of CO₂ (pCO₂) related to climate change have negative consequences for fish behaviour. Freshwater fishes may experience similar increases in pCO₂ due to a number of different mechanisms, but there is a paucity of information on how freshwater fishes may respond to exposure to elevated pCO₂. To define the effects of elevated pCO₂ on a free-swimming freshwater fish, 19 adult largemouth bass (Micropterus salmoides) were tagged with acoustic transmitters, held in water with pCO₂ levels of either ˜10 000 μatm or ambient pCO₂ (<100 μatm) for 5 days and released into a naturalised, earthen-bottom pond outfitted with an acoustic telemetry array. Findings indicate that largemouth bass not exposed to elevated levels of pCO₂ decreased movement over 35% during the daylight periods; however, fish exposed to elevated levels of pCO₂ did not exhibit this pattern. This difference in diel movement patterns between fish exposed to elevated pCO₂ and fish not exposed was not detectable after 11 days. Changes in home range size and daily distance travelled were not observed. However, based on an assessment of position estimates after the completion of the telemetry monitoring portion of the study, space use differed for fish exposed to elevated pCO₂. Exposure to elevated pCO₂ therefore can have consequences for some movement behaviours of freshwater fish and this may influence a variety of ecological processes including energetics, foraging and predator–prey dynamics. CO₂-induced alterations to behaviour should recover upon a return to ambient water.