Summary
Electric fish handling gloves (FHGs) have been developed to immobilize fish during handling, with the potential benefit of reducing the time needed for sedation and recovery of fish relative to chemical anaesthetics. We examined the secondary stress responses (i.e., hematocrit, blood glucose, lactate, and pH) and reflex responses of Largemouth Bass Micropterus salmoides that were immobilized in water using electric FHGs for multiple durations (0, 30, and 120 s) relative to fish that were handled using only bare hands in water. We also evaluated the efficacy of the immobilization by quantifying the number of volitional movements that were observed during handling. Our findings suggested that when FHGs were used, fish tended to remain still (i.e., to show full reflex impairment) during handling relative to controls. Fish that were held with FHGs showed negligible reflex impairment immediately after the electricity was terminated. After a 30‐min posttreatment retention period, blood chemistry and ventilation rates were similar between fish held with FHGs and those held with bare hands. This study supports the notion that electric FHGs are a safe and effective tool for practitioners who need to temporarily immobilize fish for handling, enumeration, or performing various scientific procedures.
Methodology
Study area and specimen collection
Largemouth Bass represented a suitable study species, as they are easily captured, ubiquitous, and well‐studied with regard to the physiological effects of angling (e.g., Cooke et al. 2003; White et al. 2008; Gingerich and Suski 2012; O'Connor et al. 2013). Largemouth Bass are also cultured throughout North America, where they are frequently stocked to support recreational fisheries (Morris and Clayton 2009), rendering this study valuable to aquaculturists and hatchery managers.
Our study was conducted out of the Queen's University Biological Station on Lake Opinicon (44°35′6.4278″N, −76°17′47.6622″W), Ontario, Canada. Fish were collected from May 1 to May 4, 2015, at water temperatures of 12–19°C (mean = 17.0 ± 2.0°C) by using medium‐action fishing rods, spinning reels, and 6.8‐kg‐test fishing line. Terminal tackle was standardized to size‐1/0 octopus hooks (Cooke et al. 2003), which were baited with pink, artificial soft‐plastic worms rigged in the “wacky” fashion (i.e., the hook placed through the center of the plastic worm). Fight duration was limited to 30 s or less, and angling time was recorded as the time between the moment of hooking and the moment the fish was landed in a rubberized net (following Lennox et al. 2015).
Experimental design
Fish were divided into five treatment groups: control (n = 14), handling with bare hands for 30 s (n = 13), handling with bare hands for 120 s (n = 15), handling with electric FHGs for 30 s (n = 13), and handling with electric FHGs for 120 s (n = 14). “Control” fish received no handling treatment and were immediately placed in holding tanks and monitored via the same protocol as treatment fish. Fish in both the electric FHG treatments and the bare‐handed treatments were experimentally handled immediately after landing and de‐hooking while in the water. Handling protocol consisted of holding the fish around the caudal peduncle and posterior to the opercular cover with wetted hands or gloves, as per recommendations of the electric FHG manufacturer (Smith‐Root, Inc., Vancouver, Washington). Gloves were set to deliver a current of 4 mA, the lowest power setting (higher settings included 6.3, 10, 16, and 25 mA). Fish were held in a padded, V‐shaped sampling trough (see Cooke et al. 2005 with their heads submerged in lake water to allow gill ventilation. “Escape attempts” were counted as the number of volitional movements made by the handled fish, indicating suboptimal immobilization. After the handling treatment, fish were immediately transferred to 60‐L, onboard holding tanks filled with lake water and were monitored for 30 min. Lake water was transferred to the holding container immediately before holding, and the temperature was monitored during the holding period. Over the recovery period, ventilation rates for all treatment groups were measured by observing opercular movements at seven time intervals: 0, 2, 5, 10, 15, 20, and 30 min (following White et al. 2008). Ventilation rates were monitored for 30 s at each time point and were doubled to calculate the number of ventilations per minute (White et al. 2008).