When dealing with invasive fishes, permanent barriers may inhibit spread, but may not be feasible due to costs and logistical constraints. Alternatively, non-permanent barriers using electricity, light, sound, pressure, bubbles, and CO2 are being developed and deployed in efforts to limit and prevent the spread of aquatic invasive species or to achieve fish guidance and conservation. However, the effectiveness of these barriers is quite variable and testing is often lacking for both invasive and native species. We conducted a laboratory experiment to investigate the impact of vertical electric barrier on behaviour of Rainbow Trout, Oncorhynchus mykiss. In response to electric current, Rainbow Trout responded by significantly decreasing passage through the electric barrier zone and spending more time away from the electric barrier when it was turned on during the stimulus period compared to pre-stimulus period. Moreover, when interacting with electric barrier, Rainbow Trout exhibited certain behaviours (e.g. stunned and remained on the same side of the barrier, stunned and crossed the barrier) more than others (e.g. approach and retreat, deflected, and paralyzed). Moreover, it appears that Rainbow Trout remained distant from the electric barrier even after the electric barrier was turned off. Our results indicate that relatively weak electric gradient (i.e. voltage gradient: 0.2 – 0.4 v·cm−1, power density: 3 – 42 µW·cm−3) can inhibit the movement of Rainbow Trout. Our results also highlight the importance of detailed investigation of behavioural responses of target species when evaluating and considering fish-deterrent or guidance technologies.

Introduction

Invasive species are a growing global concern given their significant ecological and economic costs (Palmer et al., 2004). These costs include loss of ecosystem services, loss of important native species, ecosystem degradation, and management costs (Pimentel et al., 2005). For example, Bighead Carp Hypothalmichthys nobilis, Silver Carp Hypothalmichthys molitrix, Grass Carp Ctenopharyngodon idella, and Black Carp Mylopharyngodon piceus, collectively known as Asian carps, have recently become established in the Mississippi River basin and have had significant ecological and socio-economic impacts on its ecosystem (Kolar et al., 2005; Chapman and Hoff, 2011). Potential movement of these invasive species from the Mississippi River basin into the Great Lakes basin is a concern as they are expected to have significant ecological and economic impacts once established (Cudmore et al., 2012, 2017; Kim and Mandrak, 2016; Currie et al., 2017). Extensive research and management efforts are underway by both US and Canada to assess and mitigate invasion risks of Asian carps into the Great Lakes (Asian Carp Regional Coordinating Committee (ACRCC), 2017; Fisheries and Oceans Canada (DFO), 2017), including both target and non-target species.

Deterrent systems can guide fishes away from sources of mortality but can also be used to inhibit fishes from spreading (e.g. hydropower turbines; Adams et al., 2001). There are two main groups of systems: physical and nonphysical barriers. Physical barriers, such as vertical or horizontal bars, screens, barrier nets, and low-head dams, physically prevent fish movement (Taft et al., 2001). However, physical barriers are prone to fouling and, hence, require regular maintenance. Moreover, these systems can be costly depending on scale, inhibit economic activities, such as shipping, and may permanently alter landscapes and flow regimes. In comparison, nonphysical barriers use behavioural stimuli to divert fishes and may be species specific in some instances (Noatch and Suski, 2012). Nonphysical barriers have been developed and deployed to exclude fishes from undesirable locations using a combination of electricity, sound, strobe light, bubbles, carbon dioxide, electricity, and pulse pressure (Maes et al., 2004; Noatch and Suski, 2012; Kates et al., 2012; Ruebush et al., 2012; Johnson et al., 2014; Romine et al., 2015; Vetter et al., 2015, 2017; ACRCC, 2017; Zielinski and Sorensen, 2017).

Electric current has a long history of use in fisheries management and has recently gained more interest due to increasing numbers of invasive species (ACRCC, 2017; DFO, 2017). At first, alternating current (AC) was used to block and guide Sea Lamprey Petromyzon marinus (Baker, 1928; Applegate et al., 1952), but resulted in excessive non-target fish mortality (Erkkila et al., 1956). Adult Chinook Salmon Oncorhynchus tshawytscha and Sockeye Salmon Oncorhynchus nerka have been diverted into hatchery holding ponds with AC barrier (Burrows, 1957; Palmisano and Burger, 1988). Subsequently, pulsed direct current (PDC) has been used for fish blockage because the electric field is not continuous and polarities do not reverse; hence, the potential for injury is reduced (McLain, 1957; Reynolds and Kolz, 2012). Most PDC fields are produced by horizontal electrodes mounted on the stream bottom to shelter electrodes from stream debris. The primary difference between horizontal and vertical electrodes is the plane in which the electric field varies (Johnson and Miehls, 2014; Johnson et al., 2014; Johnson et al., 2016). Although electric barriers have been used to restrict movement or to attract into a portable trap Sea Lamprey (Katopodis et al., 1994; Johnson et al., 2014; Johnson et al. 2016), Common Carp Cyprinus carpio (Verrill and Berry, 1995; Kim and Mandrak, 2017), Grass Carp (Maceina et al., 1999), Ruffe Gymnocephalus cernua (Dawson et al., 2006) and, more recently, Asian carps (Parker et al., 2015), and to guide out-migrating Sea Lamprey and Rainbow Trout Oncorhynchus mykiss, information on effectiveness of electric barrier, settings, target species, size, and behaviour is still limited and, in some cases, not known (Reynolds, 1996; Noatch and Suski, 2012; Johnson et al., 2014; Parker et al., 2015; Johnson et al., 2016; ACRCC, 2017; DFO, 2017).

To evaluate the effectiveness of a vertical electric barrier as a means to prevent or guide fish movement, a comprehensive understanding of how target species interact with this barrier is required. For our research, Rainbow Trout is used as a model organism for non-target species, which is native to North America (Scott and Crossman 1973). However, Rainbow Trout is considered as an invasive species in many parts of the world including United States of America, Japan, New Zealand, and Venezuela to Chile (Kurt et al. 2001; Rahel et al. 2008). Laboratory trials were conducted to examine the responses of Rainbow Trout to a vertical electric barrier. We specifically investigated if an electric barrier influences Rainbow Trout in: (1) decreasing crossing rates over an electric barrier zone; (2) exhibiting certain type of behaviours more than others when interacting with the electric barrier; and, (3) spending more time away from the electric barrier (i.e. space use within the experimental tank).

Materials and Methods

Experimental subjects

Rainbow Trout (∼2.5 g of weight) were initially purchased from a hatchery (Alma Aquaculture Research Station, Guelph, Canada) in March 2014 and reared and maintained at the Aquatic Life Research Facility in the Canadian Centre for Inland Waters (CCIW), Burlington, Ontario, Canada. Prior to the study in 2015, all fish were maintained in recirculating tanks (∼714 – 1606 l) with dechlorinated water (water temperature 12-15 °C; 12 h light: 12 h dark photoperiod) and were fed (0.5 - 1.0% of fish weight) daily with commercial fish food (Profishent Trout Chow, Martin Mills, Inc).

Fish tagging

Prior to each trial, all fish were individually marked using a numbered and coloured floy tag (FD-94, Floy Tag & Mfg. Inc., Seattle, USA). Fish were anaesthetized using a portable electroanaesthesia system (PES; Smith-Root, Inc., Vancouver, USA). The system included a large portable cooler (100 cm X 46 cm X 38 cm) with anode/cathode plates at either end (distance between anode and cathode = 80 cm), both connected to a control system that is capable of regulating wave form supplied, duty cycle, and duration. The electrosedation setting (Smith-Root, Inc. 2009; Kim et al., 2017) used to anaesthetize the fish was “burst of 3”, duty cycle 62%, burst frequency 500Hz, cycle frequency 30Hz, and a voltage of 100 V. Seven to 10 shocks were administered to each fish until stage IV of sedation was achieved (Summerfelt and Smith, 1990). In general, fish were oriented at horizontal angles towards cathode or anode plates (0° or 180°, Rous et al., 2015; Kim et al., 2017). Stage IV sedation is associated with the total loss of equilibrium, muscle tone, and responsiveness to visual and tactile stimuli but maintenance of a steady, although reduced, opercular ventilation rate. Prior to tagging, all fish were measured and weighed to ensure that fish would be similar in size for each trial. One of the four coloured floy tags was then inserted beside the dorsal fin between the pterygiophores using a floy-tag inserting gun (Floy Tag & Mfg. Inc., Seattle, USA). Following tagging, fish were placed in a recovery tank and monitored until they were able to maintain proper balance before being returned to their holding tanks. All fish were given at least four days to fully recover from any effects of the tagging procedure before being used in experiments (Summerfelt and Smith, 1990; Kim et al., 2017). This provided all fishes time to recover and resume “normal activity” under the laboratory conditions after experiencing electric shock during the tagging procedures. Overall, electroanaesthesia reduced handling stress and facilitated the logistics of this experiment (Summerfelt and Smith 1990; Kim and Mandrak 2017; Kim et al. 2017). Moreover, the addition of both pre-stimulus and post-stimulus periods allowed identification and accounting for any potential confounding effects of prior experiences and physical presence of electric barrier.

Experimental set-up

Experiments were conducted in a rectangular tank (3.56 m X 1.1 m X 0.39 m). The tank was evenly divided into six grids using nuclear-grade red duct tape for accurate positional scoring (Fig. 1). During the acclimation period, air stones were left in the tub to provide sufficient oxygenation and a low flow of freshwater was also left on to maintain a water temperature of around 14 °C, as well as to prevent the build-up of waste products. Average ambient water conductivity was 250.44 µS·cm−1 (±3.73 µS·cm−1). Blinds were used to cover the experimental tanks and to prevent potential disturbance.

Figure 1.

A) Experimental tank set-up and scoring grids, B) photo of experimental tank set-up

Figure 1.

A) Experimental tank set-up and scoring grids, B) photo of experimental tank set-up

Electric barrier

A portable electric barrier system (Neptun, Procom System S.A., Wroclaw, Poland) was used in the trials. The barrier consisted of two elements: a power control unit that supplies the electric voltage; and, the vertical electrodes in the water. Two electrode lines (one cathode and one anode) were placed in the centre of the experimental tank so that the electric field divided the tub into two ‘safe zones’ (i.e. location 3 and -3) of around 110 cm x 150 cm on either end (Fig. 1). Two electrodes were attached to each line for a total of four electrodes in the whole system. The cathode (diameter = 4.1 cm) and the anode (diameter = 3.81 cm) were made of hollow, stainless steel rods. The electric field settings used in this experiment were 30 volts, 10 pulses, pulse length = 0.3 ms, gap length = 10 ms, repetition = 150 ms creating a duty cycle of 2% (Neptun, Procom Systems, S.A.). A targeted voltage gradient of 0.2 - 0.4 V·cm−1 was created with these parameters within location 0 across depths for the stimulus period (Kim and Mandrak 2017). These settings were selected with inputs from Procom Systems personnel, Fishways Global personnel, experienced biologists at Fisheries and Oceans Canada, and consideration of similar studies (Johnson and Miehls, 2014; Johnson et al., 2014).

Peak voltage gradients (V·cm−1) in the experimental tanks were measured with a 10 cm probe connected to an oscilloscope (Fluke 190 series Scopemeter, Mississauga, Canada) at depths of 15 and 39 cm (Johnson et al., 2014; Procom Systems S.A.). Voltages were measured over a 10 cm distance, so the measurements were divided by 10 (Johnson et al., 2014). Summary information are reported in Kim and Mandrak (2017). In addition, the power density (µW·cm−3) was calculated as peak voltage gradient squared times ambient conductivity (Kolz, 1989; Johnson et al., 2014). The power density ranged from 3.0 to 42.0 µW·cm−3 at the location 0 (Fig. 1).

Behavioural experiments

A total of 17 trials were conducted using a total of 51 juvenile Rainbow Trout (weight = 0.78 ± 0.18 kg, mean ± standard deviation SD, fork length = 378 ± 30 mm, n = 51) in December 1 – 24, 2015. Three individuals were introduced to the experimental tank the day before each trial, allowing the fish to acclimate to the tank for at least 16 h. Each trial consisted of three consecutive periods of 30 min: pre-stimulus, stimulus, and post-stimulus. For each period, video footage was captured for at least 30 min. The electric barrier was turned off for the pre-stimulus period, followed by a stimulus period with the electric barrier turned on. The electric barrier was then turned off for the post-stimulus period. All three periods were continuously recorded using two methods: an overhead view using a camcorder (Canon, XA25) placed over one corner of the experimental tank; and, an underwater view recorded by a camcorder (GoPro, HERO4) fixed at the opposite end of the tank (Fig. 1).

Fish behaviour was observed closely during each trial, especially during the stimulus period where the fish could be shocked in a way that prevented it from escaping the electric field. To prevent death or over-shocking of an individual in these cases, the electric barrier was turned off for a short period of time to allow for recovery and eventual exit of the barrier zone before the system was turned back on. Video recordings were extended to ensure at least 30 min of total recording time with the electric barrier turned on. If the fish did not recover within 15 minutes after failing to escape the electric field, the fish was manually removed after the electric barrier was turned off. This fish was considered ‘deceased’ and no longer counted for future positional scoring.

Data analysis

Both overhead and underwater video recordings were used simultaneously by the scorer for each trial. Total positional occurrences and total barrier crossings were quantified for each of the three periods by recording a positional score for each fish at every 30-sec interval. The scoring grid was divided into seven locations based on distance from the electric field (Fig. 1). An individual was considered to have ‘crossed’ the barrier if it moved from a negative to a positive location (or vice versa) when evaluating the summarized scoring results.

During the 30-min stimulus period, every interaction with the electric barrier was recorded and classified as one of six categories (modified from Johnson et al., 2014; Kim and Mandrak, 2017): (1) approach and retreat - a slow approach towards the barrier and slow backward movement upon sensing of the electric field; (2) deflected - a quick approach towards the barrier and a strong turn away from the electric field; (3) stunned and remained on the same side of the barrier - the fish body goes rigid but does not ultimately cross the barrier; (4) stunned and crosses the barrier - the fish body goes rigid and crosses through the barrier; (5) paralyzed - a loss of equilibrium and motor functions when entering the barrier, recovery occurs within 2 min of the barrier being turned off to allow for the fish’s escape; and, (6) death/over-paralysis - a loss of equilibrium and motor functions when entering the barrier, recovery does not occur within 2 min of the barrier being turned off and the individual may have to be manually removed from the electric field. These interactions were then tallied to determine how Rainbow Trout could be expected to react when faced with an electric barrier.

We used repeated-measures ANOVA to test the effects of electric barrier on the mean number of total crosses as within-subjects across pre-stimulus, stimulus, and post-stimulus periods. There were 17 replicates. Scores of each behaviour category were compared using a one-way ANOVA to test whether the number differed between each behaviour category. Afterwards, pairwise post-hoc Fisher’s LSD comparisons were completed for the behaviour category. We also used repeated-measures ANOVA to examine the effects of location as between-subject and proportion of time spent in each location across three time periods as within-subjects. Because not all locations were equal in size (Fig. 1), the proportion of time spent in locations 1 and -1 were combined and repeated-measures ANOVA were completed using the total of six locations (i.e. 3, 2, 1 and -1, 0, -2, -3). Prior to data analyses, all data (e.g. mean number of total crosses, scores of each behaviour, proportion of time spent) were transformed using log10 (x + 0.1) to meet the assumptions of parametric tests (Zar, 1996). All statistical analyses were conducted using SPSS 12.0.1.

Results

Crossing of electric barrier

Number of crossings by Rainbow Trout were significantly different among the three periods (repeated-measures ANOVA: within-subject, linear: F 1, 16 = 7.7, P = 0.004; Fig. 2). Initially, when the electric barrier was turned off, number of crossings were significantly higher, on average about 15 per trial. As expected, when the electric barrier was turned on during the stimulus period, number of crossings decreased significantly to about three to four per trial. During the 30 minutes after the stimulus was turned off, the number of crossings decreased even further to about one per trial, compared to previous periods (Fig. 2).

Figure 2.

Mean (± SE) number of crossings by Rainbow Trout over the electric barrier during 30 minutes of pre-stimulus, stimulus, and post-stimulus periods (n = 17).

Figure 2.

Mean (± SE) number of crossings by Rainbow Trout over the electric barrier during 30 minutes of pre-stimulus, stimulus, and post-stimulus periods (n = 17).

Behavioural interactions with electric barrier

During the stimulus period when the electric barrier was turned on, the mean number of observed behaviours differed significantly between categories (ANOVA: F 5, 96 = 33.16, P < 0.001; Fig. 3). Most frequently observed types of behaviour were stunned and stays on the same side of the barrier, and stunned and crosses the barrier (Fig. 3). The least-observed behaviours were approach and retreat, death/over-paralysis, paralyzed, and deflected (Fig. 3). There were two occurrences where fish were considered “dead or over-paralyzed”, and 15 instances where fish were paralyzed (Fig. 3).

Figure 3.

Mean (± SE) number of behavioural interactions by Rainbow Trout with the electric barrier during 30 minutes of stimulus period (n = 17). Different letters represent significant post-hoc pairwise comparisons at P <0.05.

Figure 3.

Mean (± SE) number of behavioural interactions by Rainbow Trout with the electric barrier during 30 minutes of stimulus period (n = 17). Different letters represent significant post-hoc pairwise comparisons at P <0.05.

Proportion of time spent in each location within experimental tank

Across the three periods, proportion of time spent by all three fishes differed significantly among locations (ANOVA, between-subject: F 5, 96 = 48.54, P < 0.001; Fig. 4). As expected, there was a significant interaction between three periods and locations (ANOVA, within-subject, linear, F 5, 96 = 8.08, P < 0.001; Fig. 4). Specifically, for locations farthest from the electric barrier (e.g. 3 and -3, Fig. 1), fish spent the most time on average during the stimulus period and post-stimulus period compared to pre-stimulus. In contrast, fish spent more time in locations closest to electric barrier (0, 1 and -1) during pre-stimulus period compared to stimulus period. Time spent in moderately distant location (2) did not vary significantly across three periods, whereas, in location -2 fish spent more time during pre-stimulus period compared to stimulus and post-stimulus periods (Fig. 4).

Figure 4.

Mean (± SE) proportion of time spent by Rainbow Trout in locations of experimental tank during 30 minutes of pre-stimulus (□), stimulus (■), and post-stimulus (dashed box) periods (n = 17).

Figure 4.

Mean (± SE) proportion of time spent by Rainbow Trout in locations of experimental tank during 30 minutes of pre-stimulus (□), stimulus (■), and post-stimulus (dashed box) periods (n = 17).

Discussion

Our study indicated that the use of vertical electric barrier was effective in restricting the movement of Rainbow Trout under laboratory conditions. The mean number of crossings by fish significantly decreased when the electric barrier was on. Most Rainbow Trout were stunned when coming into contact with the electric field, and then either remained in one side or crossed the barrier zone. Rainbow Trout responded to the electric barrier by significantly spending more time away from the location of the electric barrier within the experimental tank. Similarly, pulsed direct currents have been recently shown to prevent movement or guide away from the barriers freshwater fishes such as Bighead Carp, Common Carp, juvenile and adult Sea Lamprey, Gizzard Shad Dorosoma cepedianum, Rainbow Trout, Silver Carp, and Walleye Sander vitreus (Verrill and Berry, 1995; Maceina et al., 1999; Holliman, 2011; Johnson and Miehls, 2014; Johnson et al., 2014; Parker et al., 2015; Weber et al., 2016; Kim and Mandrak, 2017). Specifically, vertical electric barriers were tested for use in trapping Sea Lamprey along with Rainbow Trout and White Sucker Catostomus commersonii under field condition (Johnson et al., 2014), and guiding out Sea Lamprey along with Rainbow Trout in a raceway (Johnson and Miehls, 2014), whereas, our study examined the ability of vertical electric barrier in restricting the movement of Rainbow Trout and monitored their behaviours in detail under laboratory conditions (Kim and Mandrak 2017).

Our study revealed that low voltage gradient (Range: 0.2 – 0.4 V·cm−1) would be adequate to deter or block Rainbow Trout. Similarly, low-voltage gradients turned Rainbow Trout away in a raceway experiment (Johnson and Miehl, 2014) and Common Carp (Kim and Mandrak, 2017) or guided Sea Lamprey into traps (Johnson et al., 2016). Furthermore, this voltage gradient was sufficiently powerful to paralyze some fish and, in a couple of instances, trap the fish, potentially leading to their death if we had not rescued them. Moreover, Rainbow Trout appeared to be subdued following the stimulus period, where they continue to remain less active during post-stimulus period (30 min after the electric barrier was turned off), spending more time away from the barrier zone and not crossing the barrier zone even though electric barrier was turned off. These responses were quite different from another study on Common Carp (Kim and Mandrak, 2017), where Common Carp reduced their activity during stimulus period but increased their activity during post-stimulus period. In comparison, voltage gradients used in the Chicago Sanitary Shipping Canal (CSSC) were 0.79 to 0.91 V·cm−1 (Parker et al., 2015) compared to 0.2 to 0.4 V·cm−1 in this study. The power density in our study ranged from 3.0 to 42.0 µW·cm−3 whereas the power density estimates in the CSSC ranged from 418.1 to 960.6 µW·cm−3 (i.e. calculated using data from Parker et al., 2015), about ∼10 to 20 times greater. In addition, fishes have been observed to continuously challenge the electric barriers (Parker et al., 2015). Depending on the management goals, the use of a weaker electric field to deter or guide invasive fishes from undesirable locations should be considered to limit the potential impact on target and non-target species, including species at risk (Johnson and Miehls, 2014).

Although the vertical electric barrier in our study was effective in preventing fish from crossing the barrier, it was not 100% effective in blocking all fish at all times (Kim and Mandrak 2017). Perhaps, this was to be expected given our study design, size of experimental tank, and the use of a low-voltage setting (Kim and Mandrak 2017). For example, although our experimental tank was sufficiently large to hold three Rainbow Trout (i.e. tank was ∼1.53 m3 (∼1530 L) with electric barrier zone as 0.25 m3 (∼250 L)), it was not possible to place a buffer zone of low electric field between safe areas and electric barrier zones (i.e. high electric field). A buffer zone may provide enough space for fish to avoid, or move away from, the electric barrier. Although fish did not appear to show any preferences to specific areas (e.g. edges or middle) within the experimental tank or the presence of electric barrier (personal observation), we cannot rule out that swimming impeded by the tank wall or avoidance of inactive anodes influenced the distribution of the fish in the tank. However, the addition of both pre-stimulus and post-stimulus periods allowed identification and accounting for any potential confounding effects of prior experiences and physical presence of electric barrier in our study (Kim and Mandrak 2017). We observed many instances where fish were stunned initially, but managed to cross the electric barrier, either gliding or bursting through due to sudden shock (Kim and Mandrak, 2017). Likewise, electric barriers and guidance systems have been installed to block invasive fishes, such as Sea Lamprey and Asian carps; however, in cases for Sea Lamprey, most applications were decommissioned because they did not block 100% of Sea Lamprey, presumably due to periodic floods, power outages or equipment failure, and limited migration of non-target species (Swink, 1999; Lavis et al., 2003; Clarkson, 2004). In the CSSC, where a series of large horizontal electric barriers have been set up to deter the movement of Asian carps, there are concerns about whether electric barriers are 100% effective considering there may be periodic floods, power outages, and barges providing potential refuge under the metal hull (Holliman, 2011; Parker et al., 2015; Davis et al., 2016). This demonstrates the need to consider the size of electric field, potential responses of target species, and field logistics installation and operation of electric barrier. Nonetheless, the specific responses of Rainbow Trout and settings would be valuable to managers depending on the purpose of study or management action (Johnson et al., 2014), especially for power facilities (e.g. hydroelectric power generation dam, nuclear power plant) and their water intakes and fish impingement, and implications for target and non-target species (Johnson and Miehls, 2014; Parker et al., 2015; Johnson et al., 2016).

Conclusions

Overall, our study found that vertical electric barrier was effective in inhibiting the movement of Rainbow Trout under laboratory conditions. While we should be careful not to extrapolate our findings to other species or larger field scales until further research is completed, our study provides valuable insights on how Rainbow Trout responds behaviourally to vertical electric barrier, especially under relatively low voltage settings. This would be important to managers using an electric barrier to prevent movement of fishes or to guide them away from undesirable locations.

Acknowledgements

This research was funded by Asian Carp Program at Fisheries and Oceans Canada (DFO). Becky Cudmore and Gavin Christie provided program oversight. Field crews at DFO included David Marson, D’Arcy Campbell, Brad Doyle, Monica Choy, Hadi Dhiyebi, Paul Bzonek, Catherine Chandler, Caityln Bondy, and many summer student technicians through DFO’s Federal Student Work Experience Program (FSWEP). Experiments were conducted at Aquatic Life Research Facility, Canada Centre for Inland Waters with logistic support from Alicia Mehlenbacher, Quintin Rochfort, and Jaclyn Gugelyk at Environment and Climate Change Canada (ECCC). Adrian Wodecki, Emil Kukulski, and Piotr Augustyn at Procom Systems S.A. and Matt Irvine at Fishways Global provided logistical and technical support. We thank Nick Johnson at USGS for earlier discussion and help with study design and logistic. A Visiting Fellowship from Natural Sciences and Engineering Research Council (NSERC), funded by the DFO Asian Carp Program, was provided to JK. This study was conducted according to Animal Use Protocol approved by Animal Care Committee at Canada Centre for Inland Waters.

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