There is growing interest in the use of carbon dioxide (CO 2 ) as a management tool for controlling invasive fishes.  However, there is limited published data on susceptibility of many commonly encountered species to elevated CO 2 concentrations.  Our objective was to estimate the 24-h LC 50 and LC 95 of four fishes (Rainbow Trout Oncorhynchus mykiss , Common Carp Cyprinus carpio , Channel Catfish Ictalurus punctatus , and Westslope Cutthroat Trout Oncorhynchus clarkii lewisi ).  In the laboratory, we exposed juvenile fish to a range of CO 2 concentrations for 24-h in unpressurized, flow-through tanks.  A Bayesian hierarchical model was developed to estimate the dose response relationship for each fish species with associated uncertainty, and 24-h LC 50 and LC 95 values were estimated based on laboratory trials for each species.  The minimum concentration inducing mortality differed among cold water-adapted species and warm water-adapted species groups: 150 mg CO 2 /L for Westslope Cutthroat Trout and Rainbow Trout and 225 mg CO 2 /L for Common Carp and Channel Catfish.  We observed complete mortality at 275 mg CO 2 /L (38,672 µatm), 225 mg CO 2 /L (30,711 µatm), and 495 mg CO 2 /L (65,708 µatm (CC); 77,213 µatm (CF)) for Westslope Cutthroat Trout, Rainbow Trout, and both Common Carp and Channel Catfish, respectively.  There was evidence of a statistical difference between the LC 95 values of Westslope Cutthroat Trout and Rainbow Trout (245.0 ( 222.2 to 272.2 ) and 190.6 ( 177.2 to 207.8 ) mg CO 2 /L, respectively).  Additionally, these values were almost half the estimated 24-h LC 95 s for Common Carp and Channel Catfish (422.5 ( 374.7 to 474.5 ) and 434.2 ( 377.2 to 492.2 ) mg CO 2 /L, respectively).  Although the experimental findings show strong relationships between increased CO 2 concentration and higher mortality, additional work is needed to assess the efficacy and feasibility of a CO 2 application in a field setting.

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