Summary
Fish sedation facilitates safer handling of fish during scientific research or fisheries assessment practices, thus limiting risk of injury to fish and reducing stress responses. In recent years, there has been growing interest in using electricity to sedate fish; two methods include (1) lower‐voltage, non‐pulsed‐DC fish handling gloves (FHGs) that tend to only sedate fish while the gloves are touching the animal; and (2) a comparatively high‐voltage, pulsed‐DC Portable Electrosedation System (PES) that leads to galvanonarcosis. This study compared the physiological consequences of exposure to FHGs and PES in teleost fish. Bluegills Lepomis macrochirus and Largemouth Bass Micropterus salmoides were exposed to FHGs, PES, or a handling control for a 3‐min simulated surgery. Blood was then sampled at 0.5 and 4.5 h postexposure and was analyzed for blood glucose, blood lactate, and plasma cortisol concentrations. Opercular rates were monitored during surgery, at 2 min postsurgery, and 0.5 h postsurgery. At 24 h postsurgery, time to exhaustion (via a standardized swimming chase protocol) was assessed. Fish exposed to FHGs tended to exhibit lower opercular rates than fish that were sedated with the PES during simulated surgery. Cortisol levels of Largemouth Bass treated with FHGs were higher than those of fish sedated with the PES. Glucose levels recorded for Bluegills at 4.5 h postsurgery were higher with FHGs than with the PES. In both species, lactate was lower for fish treated with FHGs than for those treated with the PES. At 24 h posttreatment, Bluegills sedated with FHGs exhibited a longer time to exhaustion than those subjected to the PES, whereas Largemouth Bass sedated with the PES exhibited a longer time to exhaustion than those sedated with FHGs. Physiological responses to treatments were inconsistent between species. Further investigation to determine the optimal electrosedation method is required.
Methodology
Study area and species
All fish were collected from shallow, vegetated bays of Lake Opinicon (Chaffey's Lock, Ontario, Canada; 44°33′32.3994″N, 76°19′40.8″W) between June and July 2016. Bluegills (mean ± SD = 159.9 ± 12.7 mm TL) and Largemouth Bass (306.6 ± 34.1 mm TL) were captured using rod and reel with a variety of plastic and live baits. These species were selected for the present study due to an abundance of literature that concentrates on centrarchids’ physiological response to stress (Mommsen et al. 1999; Trushenski et al. 2012b; Lawrence et al., in press). All experimental practices were approved by the Carleton University Animal Care Committee under guidance from the Canadian Council on Animal Care (Number 1082340).
Experimental protocol
Individual fish were placed into blacked‐out holding cells (Bluegills: 4.2 L; Largemouth Bass: 18.3 L) that were maintained on a flow‐through of natural lake water and independent aeration (McConnachie et al. 2012). Animals were allowed to acclimate for 24 h prior to any experimental proceedings. Treatment groups were randomly assigned to each fish and included either a bare‐hands control (i.e., latex gloves; Bluegills: n = 12; Largemouth Bass: n = 12), anesthesia by way of FHGs (Bluegills: n = 13; Largemouth Bass: n = 12), or anesthesia with the PES (Bluegills: n = 11; Largemouth Bass: n = 13). All fish treated with the bare‐hands control and the PES unit were handled with latex gloves during simulated surgery. Control fish received no anesthesia and were immediately placed dorsal‐side down in a surgery trough, with the gills submerged under continuously flowing water, to begin the trial. Fish exposed to FHGs were placed dorsal‐side down in a surgery trough, with the gills submerged underwater (continuous flow). The FHGs were positioned on the fish's head and caudal peduncle (suggested glove position; Smith‐Root 2016) and were turned on at the lowest current setting (4 mA). The current setting was increased (6.3, 10, 16, and 25 mA) until full‐body flinches stopped (as per instructions; Smith‐Root 2016), eliciting stage IV sedation with complete immobilization and continuous opercular respiration (Summerfelt and Smith 1990). Fish that were exposed to the PES treatment were placed in the exposure tank that was filled with lake water. The fish was positioned perpendicularly to the unit's electrodes (Rous et al. 2015) before administering treatment. At this time, the PES unit was activated, and the fish was exposed to an electrical current (pulse type = standard PDC; frequency = 40 Hz; voltage = 200 V; duty cycle = 25%; duration = 3 s). After sedation with the PES, the fish was transferred to a surgery trough, with the gills submerged underwater (continuous flow).