Chemical and Electrical Approaches to Sedation of Cobia: Induction, Recovery, and Physiological Responses to Sedation

Abstract To support the growing interest in marine fisheries research in areas such as biotelemetry, tagging, and tracking, we assessed the ability of various sedatives to facilitate this research in juvenile cobias Rachycentron canadum (∼300 g), namely, tricaine methanesulfonate (MS‐222; 150 mg/L), carbon dioxide (CO 2 ; ∼750 mg/L), eugenol (60 mg/L), benzocaine (150 mg/L), and pulsed‐DC electrosedation (100 V, 30 Hz, 25% duty cycle, 5‐s exposure). Induction times (CO 2 [z] > benzocaine [y] > eugenol [y] > MS‐222 [y] > electrosedation [x]), recovery of equilibrium (CO 2 [z] > eugenol [z] > MS‐222 [y] > benzocaine [y] > electrosedation [x]), and responsiveness to tactile stimulus (eugenol [z] > MS‐222 [y] > benzocaine [y] > CO 2 [xy] > electrosedation [x]) differed significantly among the sedative treatments (treatments with the same letters are not significantly different). Total handling time from initial sedative exposure to recovery differed among the sedatives as well (CO 2 [z] > eugenol [y] > benzocaine [x] > MS‐222 [x] > electrosedation [w]), with cumulative means ± SEs of 5.9 ± 0.2 min for CO 2 , 4.1 ± 0.2 for eugenol, 2.7 ± 0.2 min for benzocaine and MS‐222, and 1.0 ± 0.2 min for electrosedation. Physiological responses differed significantly over time, with transient increases in plasma cortisol, glucose, osmolality, and lactate that were resolved within 6 h. The overall magnitude of the physiological responses differed among sedatives, depending on the response variable; however, in each case, CO 2 elicited the greatest response. Although variations in induction and recovery times were observed, it is likely that these differences can be reasonably accommodated within the context of typical research by adjusting the sedative treatments or allowing for longer induction and recovery times as needed. Received November 18, 2011; accepted August 17, 2012