Upon arrival in a novel environment, invasive species have the potential to cause negative consequences at their new location. Rather than try to eliminate invasive species after introduction, preventing their spread is a more efficient strategy to mitigate impact. The current study used a laboratory setting to quantify the efficacy of elevated carbon dioxide (CO2) in water to act as a nonphysical barrier to deter fish movement. Our focus was on deterring the movements of silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis), but largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) were also examined to quantify the impact of elevated CO2 on native species. Exposure of all species to 30 mg·L−1 dissolved CO2 for 1 h, compared with ambient CO2 concentrations of 10 mg·L−1, resulted in an elevated stress response, along with alterations to ionic–osmotic balance. Exposure of fish to 70 mg·L−1 CO2 caused a reduction in ventilation rates after 1 h, while both silver carp and bighead carp lost equilibrium. Silver carp, largemouth bass, and bluegill also showed avoidance of CO2 at approximately 100 mg·L−1. Together, results suggest that zones of elevated CO2 have potential to deter the movement of fishes.

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Aquatic hypercarbia, either naturally occurring or anthropogenically induced, can have extensive impacts on aquatic environments and resident organisms. While the impact of acute hypercarbia exposure on the behavior and physiology of fishes has been well studied, relatively little work has examined the physiological impact and acclimation capacity of fishes to chronic hypercarbia. To better understand the impacts of prolonged hypercarbia exposure, largemouth bass were held at ambient CO2 (13 mg L(-1)) and elevated CO2 (31 mg L(-1); ≈ 21,000 µatm) for 58 days. Following this acclimation period, fish were subjected to three separate, yet complementary, experiments: (1) acute hypercarbia challenge of 120 mg L(-1) CO2 for 1 h to quantify physiological and molecular responses; (2) hypercarbia avoidance challenge to compare CO2 agitation and avoidance responses; and (3) swim performance challenge to quantify burst swimming performance. Acclimation to 31 mg L(-1) CO2 resulted in a significant constitutive upregulation of c-fos expression in erythrocytes, combined with significant constitutive expression of hsp70 in both gill and erythrocytes, relative to controls. Largemouth bass acclimated to elevated CO2 also had a reduced glucose response (relative to controls) following an acute CO2 exposure, indicating a reduced stress response to CO2 stressors. In addition, largemouth bass acclimated to elevated CO2 conditions required 50 % higher CO2 concentrations to illicit agitation behaviors and displayed prolonged burst swimming abilities in high CO2 environments relative to controls. Together, results demonstrate that largemouth bass exposed to chronic hypercarbia may possess a physiological advantage during periods of elevated CO2 relative to naïve fish, which may permit increased performance in hypercarbia.

One of the most severe impacts of urbanization on aquatic systems is the increasing presence of low oxygen environments caused by anthropogenic sources of pollution. As urbanization increases nationally and globally, it is becoming exceedingly important to understand how hypoxia affects aquatic fauna, especially fish species. In an effort to better understand the impacts of prolonged hypoxia on fishes, largemouth bass were held at 3.0 and 9.0 mg L⁻¹ for 50 days, which has previously shown to be temporally sufficient to impart plastic phenotypic changes. Following the holding period, fish from each group were subjected to a low dissolved oxygen (DO) challenge of 2.0 mg L⁻¹ for 6 h, and their physiological and hematological parameters were compared with control fish held for 6 h with no change in DO. There were no differences in the physiological stress responses between the two holding groups; however, the low oxygen holding group had increased hemoglobin and hematocrit levels following the 6-h low oxygen challenge compared with the high oxygen group. These results suggest largemouth bass exposed to chronic low oxygen conditions, either naturally or anthropogenically, may possess a beneficial advantage of increased oxygen uptake capacity during periods of low oxygen.

Projecting sound into navigational locks has been suggested as a promising way to block the upstream movement of invasive species of carp (family Cyprinidae). This possibility is promising because carp have a good sense of hearing compared to non-ostariophysian fishes. Although the broadband sound of an outboard motor has been shown to repel several species of carp in laboratory arenas, its efficacy in a navigational lock is unknown. This study tested whether wild-caught Common Carp Cyprinus carpio are repelled by this sound in a lock chamber in a similar manner to that observed in laboratory studies. We found that while the sound of a 40-hp outboard motor repelled Common Carp in a lock the first time it was tested, the fish stopped responding after that, suggesting that they had habituated. This result differed from that of a laboratory study that used the same sound at the same volume and found responses to persist for three exposures before dissipating. Many factors, including the use of wild Common Carp already familiar with outboard motor sounds and differences in background noise, may have been responsible for differences between laboratory and field results. There is a need for more field tests using other sounds and carp species.

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