Carbon dioxide as an under-ice lethal control for invasive fishes

Resource managers need effective tools to control invasive fish populations. In this study, we tested under-ice carbon dioxide (CO₂) injection as a novel piscicide method for non-native Silver Carp (Hypophthalmichthys molitrix), Bighead Carp (Hypophthalmichthys nobilis), Grass Carp (Ctenopharyngodon idella), Common Carp (Cyprinus carpio) and native Bigmouth Buffalo (Ictiobus cyprinellus). Fish were held overwinter in nine outdoor ponds (0.04 ha surface area; 340,000 L volume) treated with no CO₂ (control), 43.5–44.0 kg CO₂ (low treatment), and 87.5–88.5 kg CO₂ (high treatment). Ponds were harvested immediately after ice-out to assess survival and condition. Resulting survival in low (mean = 32%) and high (mean = 5%) CO₂-treated ponds was significantly lower than untreated control ponds (mean = 84%). Lethal efficacy varied across species with no Bighead Carp, Silver Carp, or Bigmouth Buffalo surviving the high CO₂ treatment. External infections were observed more frequently after CO₂ treatments (means = 49–67%) relative to untreated ponds (mean = 2%), suggesting a secondary mechanism for poor survival. This study demonstrates that CO₂ can be used as a lethal control for invasive fishes, but effectiveness may vary by species and CO₂ concentration.