Fisheries managers have a growing interest in the use of carbon dioxide (CO₂) as a tool for controlling invasive fishes. However, limited published data exist on susceptibility of many commonly encountered species to elevated CO₂ concentrations. Our objective was to estimate the 24-h 50% lethal concentration (LC₅₀) and 95% lethal concentration (LC₉₅) of CO₂ for 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 CO₂ concentrations for 24 h in unpressurized, flow-through tanks. We developed a Bayesian hierarchical model to estimate the dose-response relationship for each fish species with associated uncertainty, and estimated 24-h LC₅₀ and LC₉₅ values 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 CO₂/L for Westslope Cutthroat Trout and Rainbow Trout and 225 mg CO₂/L for Common Carp and Channel Catfish. We observed complete mortality at 275 mg CO₂/L (38,672 microatmospheres [μatm]), 225 mg CO₂/L (30,711 μatm), and 495 mg CO₂/L (65,708 μatm [Common Carp]; 77,213 μatm [Channel Catfish]) for Westslope Cutthroat Trout, Rainbow Trout, and both Common Carp and Channel Catfish, respectively. There was evidence of a statistical difference between the 24-h LC₉₅ values of Westslope Cutthroat Trout and Rainbow Trout (245.0 [222.2–272.2] and 190.6 [177.2–207.8] mg CO₂/L, respectively). Additionally, these values were almost half the estimated 24-h LC₉₅ values for Common Carp and Channel Catfish (422.5 [374.7–474.5] and 434.2 [377.2–492.2] mg CO₂/L, respectively). Although the experimental findings show strong relationships between increased CO₂ concentration and higher mortality, additional work is required to assess the efficacy and feasibility of a CO₂ application in a field setting.