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The duration spent in air-equilibrated and TDG supersaturated channels by rainbow trout (Oncorhynchus mykiss) from two strains; a Fraser Valley, n = 31, b Blackwater n = 33, and c both strains combined, n = 64 in a two-channel flume. Each point is the sum of the durations for two trials for a single fish, where we switched air-equilibrated and TDG supersaturated treatments between channels for those two trials. There was no significant effect of channel or trial sequence on duration. Gray lines connect paired observations for individual fish. The combined duration of the two trials for each fish was 240 s; fish also had the choice to spend time in an arena with an intermediate TDG level that connected the two channels
Source publication
We investigated whether individual rainbow trout (Oncorhynchus mykiss; 9–53 g) avoid a potentially lethal level of total dissolved gas (TDG) supersaturation using lateral movements during an acute exposure. As there is no mechanism by which fish can detect and avoid TDG supersaturation in shallow water, we hypothesize that rainbow trout do not dire...
Citations
... Healthy hearts enable fish to sustain high-intensity activities and choose challenging routes through the fishways. However, TDGS exposure can lead to the formation of gas bubbles in the bloodstream, impairing heart function, and interfering with fish's free selection of trajectories (Pleizier et al., 2021). Flow information plays a crucial role in guiding fish through aquatic environments (White and Mefford, 2002). ...
Total dissolved gas supersaturation (TDGS) due to flood or hydropower station discharge adversely affects the swimming performance of migratory fish, thereby reducing passage efficiency. This study assessed the swimming performance of bighead carp in an experimental vertical slot fishway under varied slot flow velocities of 0.2, 0.25, and 0.3 m/s after 2 h of exposure to different levels of TDGS water. The results demonstrated that increased TDGS levels and flow velocities significantly reduced the fish passage efficiency. Specifically, passage success rates reached 61%, 48%, 37%, and 37% at TDGS levels of 100%, 110%, 120%, and 130% respectively, at a flow velocity of 0.2 m/s. At flow velocities of 0.2, 0.25, and 0.3 m/s with 100% TDGS water, success rates were 61%, 53%, and 47%, respectively. Moreover, increased TDGS levels and increased flow velocities notably extended the passage time in the fishway. Both TDGS levels and fishway flow velocities significantly influenced the swimming trajectories of the fish. Preferences for flow velocities were notably affected by the TDGS levels, whereas preferences for turbulent kinetic energy were affected by both the TDGS levels and the velocities of the fishway flow. In this study, an evaluation method was developed to assess the adverse effects of TDGS on fish passage efficiency based on the following critical parameters: passage success rate, time, trajectory, and preferred hydraulic factor. This study offers valuable insights for optimizing operations and fishway management to enhance fish protection.
... Mortality can occur when tissue damage is severe [8,9]. Although fish can avoid the effects of elevated TDG by seeking depths that collapse internal bubbles [10,11], the literature is mixed as to whether fish sense elevated TDG and actively seek compensatory depths (e.g., [12,13]). Regardless, substantial fish kills due to elevated TDG have been observed below multiple dams [14][15][16]. ...
When water is spilled over dams, atmospheric gases can become entrained, resulting in supersaturated water. Total dissolved gas (TDG) > 110% saturation can cause gas bubble trauma (GBT) in fish. The negative effects of GBT include increased buoyancy, decreased swimming performance, and possible mortality. The lower Clark Fork River (LCFR) in Idaho frequently has TDG > 110% saturation due to the spill at Cabinet Gorge Dam as well as from upstream facilities. Spillway crests on Cabinet Gorge Dam were modified to reduce TDG production and the potential harm from GBT. To evaluate the effectiveness of spillway crest modifications, relationships between river discharge and measured TDG were developed pre-and post-modification and used to calculate the predicted TDG in the LCFR pre-and post-modification under two spill season discharge scenarios. The predicted TDG for the scenarios was used with an established TDG-GBT relationship for the LCFR to estimate the expected GBT incidence. Generally, TDG was lower post-modification, and the discharge at which 110% and 120% saturation were exceeded increased by about 198 m 3 /s. Modification also reduced the number of days with elevated TDG. The lower TDG post-modification resulted in significant (p < 0.05) reductions in the probability of observing GBT. The modification of Cabinet Gorge Dam spillway crests reduced TDG production over a range of discharges and has resulted in improved conditions for fish downstream of the dam. Key Contribution: This work demonstrates how modifying spillways on dams can reduce total dissolved gas production and anticipated rates of gas bubble trauma in fish. Work such as this can provide dam operators and fisheries managers with important information for evaluating the success of total dissolved gas reduction projects.
... TDG supersaturation likely reduces the critical or burst capacity of species such as the Chinese sucker (Myxocyprinus asiaticus), Prenant's schizothoracin (Schizothorax prenanti), and grass carp (Ctenopharyngodon idella) [7,33,66]. Prenant's schizothoracin can detect and avoid areas of high TDG through horizontal avoidance [65], whereas rainbow trout do not exhibit any avoidance behaviour [49]. Additionally, fish that experience TDG supersaturation significantly change their responses to hydraulic factors and their movement trajectories within fishway flow fields [70]. ...
During the flood season, high dam discharge rates result in total dissolved gas (TDG) supersaturation. This condition causes gas bubble trauma and can lead to fish mortality, which poses a significant threat to downstream river ecosystems. Assessing the ecological risks of TDG supersaturation is a challenge in waterpower-intensive river basins worldwide. Few studies have explored the impact of TDG supersaturation on fish behaviours, such as aggression and memory, which are crucial for feeding, reproduction, and predator avoidance. In this study, behavioural tests were conducted in a T-maze to investigate the effects of acute TDG supersaturation on swimming behaviour, aggression, and memory in medaka (Oryzias latipes). The results demonstrated that medaka exposed to TDG levels of 115% and 130% for 2 h had significantly reduced swimming performance.At TDG levels of 100%, 115% and 130%, medaka activity rates in the mirror arm of the maze in the mirror test were 44.34 ± 12.88%, 40.27 ± 15.44% and 35.35 ± 16.07%, respectively. Similarly, the activity rates of medaka in the active stimulus arm of the maze in the memory test were 50.35 ± 14.75%, 40.76 ± 12.51% and 35.35 ± 18.47%, respectively. The behaviour of medaka changed with increasing TDG supersaturation. These findings contribute to the development of an ecological risk assessment model for TDG supersaturation based on memory and aggression in fish and provide data for developing management strategies to mitigate the adverse effects of TDG supersaturation.
... Mortality can occur when tissue damage is severe [8,9]. Although fish can avoid the effects of elevated TDG by seeking depths that collapse internal bubbles [10,11], the literature is mixed as to whether fish sense elevated TDG and actively seek compensatory depths (e.g., [12,13]). Regardless, substantial fish kills due to elevated TDG have been observed below multiple dams [14][15][16]. ...
When water is spilled over dams, atmospheric gasses can become entrained resulting in supersaturated water. When total dissolved gas (TDG) exceeds 110% saturation, gas bubble trauma (GBT) can result in fishes. Negative effects of GBT include increased buoyancy, decreased swimming performance, and possible mortality. The lower Clark Fork River in Idaho frequently has TDG levels > 110% saturation due to spill at Cabinet Gorge Dam. Five spillway crests on the dam were modified to reduce TDG production and the potential harm from GBT. To evaluate the effectiveness of the spillway crest modifications, relationships between total river discharge and measured TDG were developed pre- and post-modification. These relationships were used to calculate the predicted TDG in the lower Clark Fork River pre- and post-modification under median and 75th percentile spill season discharge scenarios. The predicted TDG for the scenarios was then used with an established TDG-GBT relationship for the lower Clark Fork River to estimate the expected GBT incidence pre- and post-modification. In general, TDG was less post-modification with the discharge at which 110% saturation was exceeded increasing by about 198 m3/s. Modification also reduced the number of days with TDG > 110% by 7 and 14 days for the median and 75th percentile scenarios respectively. The lower TDG post-modification resulted in significant reductions in the probability of observing GBT. The results indicate that the modification of Cabinet Gorge Dam spillway crests reduced TDG production over a range of discharges and has resulted in improved conditions for fishes downstream of the dam. Species with relatively high GBT incidence like non-native Rainbow Trout Oncorhychus mykiss and Brown Trout Salmo trutta and native Westslope Cutthrout Trout O. lewisi and Peamouth Mylocheilus caurinus are the most likely to benefit from the reduced TDG conditions.
Keywords: Behavior, Fisheries/Habitat, Physiology, Water Quality
... Consequences of TDG supersaturation and response behavior of local fish species and other aquatic lifeforms are ongoing research topics (see e.g. [10,11,[15][16][17][18][19]). ...
Artificial total dissolved gas (TDG) supersaturation is a potentially lethal threat to the aquatic ecology downstream of hydropower plants. The severity of this threat dependents on the actual saturation level as well as on the duration of the event. Natural degassing is highly influenced by the river’s morphology and characteristics, and is in most cases insufficiently slow. To protect fish and aquatic invertebrates from gas bubble disease, a direct consequence of TDG supersaturation, the use of ultrasonic degassing to mitigate TDG supersaturation is investigated. In this process, a high-power ultrasonic field is introduced into the water, leading to an immediate reduction of the TDG saturation level. Experiments are conducted at the Waterpower Laboratory at NTNU, Norway. Within an open flume, water is channeled past an ultrasonic transducer, which introduces an acoustic field with a frequency of 20 kHz. The flow rate in the flume is adjustable, and two different flow rates are tested. In addition, the dependency of the degassing process on the acoustic power is investigated. Results indicate a strong dependency on the acoustic power, with the highest tested powers resulting in the largest reduction in TDG saturation level. The flow velocity appears to have a positive effect on the degassing efficiency as well, even though this effect is minor compared to the effect of the acoustic power. A continuous effect of the acoustic degassing in form of a gas bubble cloud leading to increased liquid-gas mass transfer is observed.
... TDG supersaturation likely reduces the critical or burst capacity of species such as the Chinese sucker, Prenant's schizothoracin, and grass carp (Jia, 2016;Wang et al., 2018;Cao et al., 2022). Some species can detect and avoid high TDG areas through horizontal avoidance (Wang et al., 2015), while others do not exhibit any avoidance behavior (Pleizier et al., 2021). Additionally, sh experiencing TDG supersaturation stress show signi cant changes in their responses to hydraulic factors and movement trajectories within shway ow elds. ...
During the flood season, high dam operations for flood discharge result in total dissolved gas (TDG) supersaturation. This condition causes gas bubble trauma (GBT) and can even lead to fish mortality, posing a significant threat to downstream river ecosystems. Assessing the ecological risks of TDG presents a major challenge in water power-intensive river basins worldwide. Limited research has explored the impact of TDG on fish behaviors such as aggression and memory, which are crucial for feeding, reproduction, and predator avoidance. This study investigated the effects of acute TDG supersaturation stress on swimming behavior, aggression, and memory in medaka. Results indicated that Medaka exposed to 115% and 130% TDG supersaturation for 2 hours showed significantly reduced swimming performance. At TDG levels of 100%, 115%, and 130%, medaka displayed activity rates in the mirror arm of 44.34 ± 12.88%, 40.27 ± 15.44%, and 35.35 ± 16.07%, respectively, and in the active stimulus arm of 50.35 ± 14.75%, 40.76 ± 12.51%, and 35.35 ± 18.47%, respectively. As TDG levels increased, both aggression and memory in medaka significantly declined. The findings of this study could contribute to developing a TDG ecological risk assessment model based on fish memory and aggression, providing essential data for ecological management strategies to mitigate the adverse effects of TDG.
... Pelagic silver carp Hypophthalmichthys molitrix and resident cyprinid and catostomid fishes in the Yangtze River system exhibited strong detection and avoidance abilities when TDG was high (i.e., >130%, Ji et al., 2021, 145%, Wang et al., 2020. Some salmonids, common focal species for TDG management and conservation actions in North America (Backman & Evans, 2002), appear able to detect high TDG levels and, in some instances, exhibit lateral movement avoidance behaviors (Pleizier et al., 2021;Stevens et al., 1980). Another method of TDG avoidance is through depth compensation, however, salmonid responses are varied (Dawley et al., 1976;Lund & Heggberget, 1985) and remain largely understudied. ...
Fish exposed to supersaturated total dissolved gas (TDG) levels can develop gas bubble trauma (GBT) which can lead to sublethal effects or mortality. Access to refugia in areas of high TDG that allows for hydrostatic (depth) compensation can mitigate exposure risk and GBT occurrence. The goals for this study were to examine resident fish habitat and depth use and assess exposure risk to elevated TDG levels related to hydropower operations in the Columbia-Kootenay system in British Columbia. Modeling was used to predict TDG levels for three operational cases (low, medium, and high spill rates). Acoustic telemetry was used to track rainbow trout Oncorhynchus mykiss (RT) and mountain whitefish Prosopium williamsoni (MW) reach and depth residency. Telemetry results did not differ among operational scenarios and aligned with known biological/life history characteristics for fluvial or fluvial-adfluvial species. Within-species MW reach residency appeared to be reflective of seasonal habitat selection for spawning, foraging, and refuge movements. Within-species RT reach residency appeared to follow habitat association patterns reflective of RT ecology. A risk assessment revealed that RT had a significantly higher TDG exposure risk relative to MW, but sufficient depth refugia habitat was available to mitigate exposure risk and GBT occurrence in both species. The results suggested that TDG exposure risk and actual risk depend on the interplay between species-specific ecology and TDG patterns generated by hydropower facilities. The ecological and TDG patterns in this study suggested that system- and species-specific studies will be required to generate detailed TDG exposure predictions for management decision-making.
Downstream hydropower plants, a change in water chemistry can lead to the occurrence of a widely unknown problem: total dissolved gas (TDG) supersaturation. It takes place when air is entrained in a water body and exposed to high pressures, which leads to gas dissolution in the water. Re-exposure to atmospheric pressure downstream the power plant results in TDG supersaturation. This is a potential danger for the aquatic environment living in these waters, as the increased saturation poses the risk of experiencing gas bubble disease (GBD). Studies about TDG supersaturation are found in North America (USA and Canada), China, Brazil, and Norway (minor studies include Austria, Germany, and Sweden). Yet, knowledge about the risk of the problem is not widespread, which leads to the repetition of mistakes. Moreover, shifting precipitation patterns induced by climate change are expected to lead to an increase in TDG supersaturation occurrences, as those are associated with flooding. An overview of methods to either prevent or mitigate the problem of TDG supersaturation downstream hydropower plants is presented and recent study results are disseminated. These include civil engineering, operational, and technical methods. Where hydropower plants are in a planning phase, this can contribute to preventing the occurrence of TDG supersaturation in the first place, while existing hydropower plants can implement different measures to reduce the risk of producing TDG supersaturation in the downstream waterways. This helps maintain the aquatic environment as well as local habitat for fish and invertebrates, and therefore counts towards hydropower taxonomy and increases social acceptance of hydropower.
Discharge of high dams may result in supersaturated total dissolved gas (TDG) in water, which could cause fish that live downstream river to suffer from gas bubble disease. If supersaturated TDG water was taken as a water source for breeding and proliferation stations, farmed fish was confined and may face more severe problems than fish living in the river. Therefore, it is critical to develop strategies to reduce the negative effects of supersaturated TDG. In this research, the adsorption effect of porous media on supersaturated TDG was explored, including biofilter adsorption experiments and previously existing activated carbon adsorption experiments. The experimental results showed that adding porous media to the water effectively accelerated the dissipation of supersaturated TDG, and the adsorption effect was associated with the specific surface area, mass density, and initial TDG saturation. To quantitively evaluate the adsorption effects of the porous media, the porous adsorption coefficient was proposed to express the adsorption rate of porous media on supersaturated TDG. The porous adsorption coefficient was related to the initial TDG saturation and the specific surface area of the porous media. The porous adsorption coefficient increased with increasing the specific surface area and decreasing initial TDG saturation. Based on this, an equation related to the specific surface area, initial TDG saturation, and the porous adsorption coefficient was developed. This equation may be used to evaluate the adsorption effect of porous media on supersaturated TDG. This study could serve as a crucial resource in reducing the adverse impacts of supersaturated TDG.
Objective
Gas bubble trauma (GBT) can occur in fish when water becomes supersaturated with gases, with effects ranging from minor tissue damage to death. Laboratory studies suggest that fish exposure to elevated total dissolved gas (TDG) at depths that compensate for gas supersaturation can result in reduced GBT incidence and that different fish species exhibit varying susceptibility to GBT. Elevated TDG levels associated with spill at Cabinet Gorge Dam in the lower Clark Fork River, Idaho, facilitated describing the incidence and severity of GBT, variables that affect GBT incidence, and the probability of observing GBT in different fish species.
Methods
Total dissolved gas and GBT data were collected during the typical spill period (i.e., April–July) in 2000, 2006, 2008, and 2017–2021.
Result
A total of 6985 fish was examined for GBT at TDG of 101–137% saturation. Incidences of GBT varied with TDG levels, and the greatest incidence of GBT was typically observed near the date with peak daily mean TDG. Logistic regression models indicated that the probability of observing GBT was affected by TDG exposure and temperature but not length. The probability of observing GBT on fish was < 0.01 when 7‐day mean TDG was 110% saturation and < 0.04 when 7‐day mean TDG was 120% saturation. The models also indicated that the probability of observing GBT at a given TDG value differed between fish species.
Conclusion
We suggest that species‐specific behavior and habitat composition in the sampled area (i.e., access to compensatory depths and locations with less TDG) were factors in our observations. We advocate that fisheries managers use a similar process to develop site‐ and species‐specific GBT probability curves where elevated TDG is an issue. These site‐specific curves can help managers evaluate the potential for population‐level effects to fisheries and need for TDG reduction or mitigation actions.
