• Brownscombe, Jacob W.
  • Parmar, Tarn P.
  • Almeida, Jessica
  • Giesbrecht, Emma
  • Batson, Jessica
  • Chen, Xiaoya
  • Wesch, Sean
  • Ward, Taylor D.
  • O‘Connor, Constance M.
  • Cooke, Steven J.


Employing science-based best angling practices is important for sustainable catch-and-release fisheries. In situations where fish lose equilibrium (unable to maintain upright posture to swim in a coordinated manner), anglers often provide assisted ventilation by hand, which typically involves maneuvering fish to move water over the gills until equilibrium is regained. However, it is unclear whether these tactics are effective at facilitating physiological and behavioural recovery and improving survival. Here we tested the efficacy of assisted ventilation techniques in two freshwater species popular for angling, largemouth bass and brook trout. Fish were captured by angling with rod and reel, and subsequently air exposed until equilibrium was lost. Treatments included maneuvering fish in a back-and-forth manner or in a constant forward motion, which were compared to controls that did not experience assisted ventilation. In largemouth bass, physiological stress values (i.e., blood glucose, lactate, pH, hematocrit) and rates of equilibrium regain were not significantly different between treatments, while all fish survived a 24-h holding period. In brook trout, fish maneuvered in a back-and-forth manner regained equilibrium fastest, but differences between treatments were not statistically significant. Further, once equilibrium was regained, brook trout often spent extended periods resting on the bottom, and likely had limited capabilities to avoid predators. We found little evidence of any physiological or behavioural benefits of two common assisted ventilation techniques that would result in improved fish survival or fitness with largemouth bass or brook trout in recreational angling scenarios. However, releasing fish in poor condition may lead to greater predation risk, so retaining fish with minimal handling until swimming capabilities return is likely the most advisable course of action.


Largemouth bass recovery

This experiment was conducted at Queen’s University Biological Station (QUBS) Lake Opinicon (44◦ 35' 6.4", −76◦ 17' 47.7") in Ontario, Canada between 01-05-2015 and 04-05-2015 at water temperatures from 15 to 22 ◦C. Largemouth bass were angled from a single shallow embayment using 2-m-long, medium-strength fishing rods and reels equipped with 6.8 kg break-strength braided fishing line. Terminal tackle included a 1/0 octopus hook, baited with a 15 cm wacky-rigged plastic worm. Upon capture, largemouth bass were air exposed in a rubberized net until equilibrium was lost. Based on initial tests and previous literature (Thompson et al., 2008), a minimum of 10 min of air exposure was required to cause largemouth bass to lose equilibrium at these water and air temperatures. In order to avoid placing fish in water to test equilibrium periodically, an initial reflex test was applied prior to testing equilibrium. The initial reflex test involved grabbing the fish by the lower jaw; the fish flexing its body indicated a positive response. Starting at 10 min of air exposure, initial reflex tests were conducted every 2 min until fish were unresponsive. Equilibrium was then tested by flipping the fish upside down in water; a positive response was indicated by the fish righting itself within 3 s. If the response was positive, air exposure continued under the same initial reflex test procedure until equilibrium was lost.

Upon equilibrium loss, additional reflex tests were conducted using RAMP methods (Davis, 2010). Five predictors were measured: tail grab, body flex, equilibrium, head complex impairment, and vestibular-ocular response (VOR). These predictors were selected because they are strong indicators of fish behavioural impairment and mortality, and also feasible for anglers to adopt (Davis 2010; Raby et al., 2012; Brownscombe et al., 2013; Brownscombe et al., 2016). Tail grab was tested by grabbing the fish’s tail in water; an attempt to escape indicated a positive response. Body flex was tested by holding the fish in air by the center of the body; flexing in attempt to escape indicated a positive response. A positive head complex response was indicated by regular opercular movement in water. Vestibular-ocular response (VOR) was tested by rolling the fish side-to-side; a positive response was indicated by the eyes moving to track level. Each indicator was scored as 0 = unimpaired and 1 = impaired and overall RAMP scores were calculated as the proportion of indicators impaired.

After RAMP assessment, fish were treated with one of three assisted ventilation techniques: control (n = 25), forward motion (n = 24), or back-and-forth (n = 24) for up to 3 min in 90 l holding containers. Fish in the control treatment were left untouched aside from equilibrium checks. Fish in the forward motion treatment were held by the center of the body while maneuvering the fish in a circular pattern in constant forward motion to generate anteriorly sourced water flow. While anglers typically manoeuvre fish in an ‘S shape’ or ‘figure-8’, the circular motion was more feasible in the holding containers and generated similar anteriorly sourced water flow. Fish in the back-and-forth treatment were held in the same manner as the forward motion treatment but manoeuvred forward and backward through the water. Equilibrium was checked every 20 s, and the recovery period concluded once equilibrium was regained, up to a maximum of 3 min.

Brook Trout Recovery

This experiment was conducted on Collins Lake in Kenauk Nature Reserve, Quebec, Canada (45◦ 44' 38.0", −74◦ 48' 24.7") on 06-10-2015 and 07-10-2015 at water temperatures ranging from 13 to 14 ◦C. Brook trout were stocked from hatcheries near Mont-Tremblant in 06-2015 and 09-2015. Fish were captured using in-line spinner lures (size 2 or 3) with barbed treble hooks and held overnight in a net pen (1.2 × 1.2 × 1.2 m, maximum density 20 fish) as a part of another study examining angling-related mortality. The following day, brook trout that were not deeply hooked and had no visible signs of injury or behavioural impairment were included in this study.

In order to elicit equilibrium loss, brook trout were air exposed in a rubberized net for a standardized 8-min period, as initial tests suggested this was a sufficient amount of time to cause equilibrium loss. After air exposure, fish were tested for the same five RAMP indicators used on largemouth bass, and separated into the same treatment groups, control (n = 21), back-and-forth motion (n = 21), and forward motion (n = 21). However, the forward motion treatment was manoeuvred in a figure-8 pattern rather than the circular pattern used with largemouth bass, and all recoveries took place in a net pen in the lake (See Fig. 1 for visualization of recovery procedure). Equilibrium was checked every 20 s, and the recovery period concluded once equilibrium was regained. Fish were released immediately after experimentation, and visually observed for up to 10 min near the release site.