Coupling carbon dioxide gas within a bubble curtain enhances its effectiveness to deter fish

Deterrent technologies are one component of preventing the spread of invasive fishes to protect aquatic ecosystems from biodiversity loss. Curtains of bubbles can act as a non-physical barrier to deter fish movements, but will not stop all species in all situations. Modifications to bubble curtains that decrease fish movements would help protect aquatic ecosystems. The current study sought to quantify whether adding carbon dioxide gas (CO₂) to a bubble curtain would enhance its efficacy to block fish. For this, a choice tank was outfitted with bubble curtains infused with either compressed air alone, or with two different concentrations of CO₂ [30 or 100 mg/L]. Passage rates and position of common carp (Cyprinus carpio, an invasive Cyprinid) and black bullhead (Ameiurus melas, a native Ictalurid) exposed to these treatments were compared. Common carp were less likely to pass a bubble curtain when CO₂ gas was used relative to the use of compressed air alone, and only 30 mg/L CO₂ was needed to reduce passage. Black bullhead passages were not influenced by the bubble curtain, even with the addition of CO₂. However, black bullhead, were found 30% further upstream of the curtain when CO₂ was used relative to the control and air alone treatments, demonstrating avoidance of CO₂. This study shows that CO₂ added to a bubble curtain will enhance its ability to block passage of invasive fish.