Predation of freshwater fish in environments with elevated carbon dioxide

Carbon dioxide (CO₂) in fresh-water environments is poorly understood, yet in marine environments CO₂ can affect fish behaviour, including predator–prey relationships. To examine changes in predator success in elevated CO₂, we experimented with predatory Micropterus salmoides and Pimephales promelas prey. We used a two-factor fully crossed experimental design; one factor was 4-day (acclimation) CO₂ concentration and the second factor CO₂ concentration during 20-min predation experiments. Both factors had three treatment levels, including ambient partial pressure of CO₂(pCO₂; 0–1000 μatm), low pCO₂ (4000–5000 μatm) and high pCO₂ (8000–10 000 μatm). Micropterus salmoides was exposed to both factors, whereas P. promelas was not exposed to the acclimation factor. In total, 83 of the 96 P. promelas were consumed (n = 96 trials) and we saw no discernible effect of CO₂ on predator success or time to predation. Failed strikes and time between failed strikes were too infrequent to model. Compared with marine systems, our findings are unique in that we not only saw no changes in prey capture success with increasing CO₂, but we also used CO₂ treatments that were substantially higher than those in past experiments. Our work demonstrated a pronounced resiliency of freshwater predators to elevated CO₂ exposure, and a starting point for future work in this area.