Currently, in the United States, there are few sedatives available to fisheries professionals that are safe, effective, and practical. Chemical sedatives, including tricaine methanesulfonate (MS‐222), carbon dioxide (CO2), benzocaine, and eugenol may be used to sedate fish, though none of these compounds are currently approved by the U.S. Food and Drug Administration as immediate‐release fish sedatives. Another option is the use of electricity to temporarily immobilize fish. Few studies have assessed the efficacy of these options for immediate‐release sedation in side‐by‐side comparisons. We evaluated the use of MS‐222 (150 mg/L), CO2 (∼400 mg/L), benzocaine (150 mg/L), eugenol (60 mg/L), and a commercially available electrosedation unit (30 Hz pulsed DC, 60 V, 25% duty cycle, 3‐s exposures) to induce hybrid striped bass (white bass Morone chrysops × striped bass M. saxatilis; 510 ± 12 g [mean ± SE]) to stage IV anesthesia or sedation. Induction times were shortest (0.2 ± 0.1 min) when electrosedation was used and longest (2.5 ± 0.1 min) when CO2 was used; the induction times for the other chemical sedatives varied (<2 min). Recovery times were longest for eugenol (5.2 ± 0.4 min postinduction) and benzocaine (4.0 ± 0.4 min); however, the difference in recovery time between these two treatments was not significant or between recovery times for benzocaine and the remaining sedatives (∼3–4 min). Physiological responses varied but were consistent with the generalized stress response. Circulating levels of cortisol, glucose, and lactate increased after sedation, and though response magnitude and duration varied somewhat among these variables, these changes were resolved within 6 h. Changes in plasma osmolality and hematocrit were less overt and varied less among the sedatives. Electrosedation may be a suitable tool for quickly sedating hybrid striped bass; however, all of the sedatives evaluated were effective at the doses and strengths used and some may be better suited to certain applications than to others.

Sedating fish before handling minimizes the risk of injury to both fish and handler and may also minimize the fish's stress response. We conducted two experiments to quantitatively compare induction and recovery times of largemouth bass Micropterus salmoides sedated with tricaine methanesulfonate (MS‐222), eugenol, benzocaine, carbon dioxide (CO2), or electrosedation (pulsed DC). We also assessed the fish's hematological profile following sedation with MS‐222, eugenol, and electrosedation. Induction times varied significantly among the sedatives evaluated; electrosedation yielded the fastest inductions (0.2 ± 0.1 min; mean ± SE) and CO2 yielded the slowest (3.6 ± 0.1 min). Times to recovery of equilibrium and responsiveness to tactile and visual–auditory stimuli also varied, ranging from 1.8 ± 0.3 to 3.7 ± 0.3 min and from 2.3 ± 0.3 to 4.0 ± 0.3 min, respectively, depending on the sedative used. Plasma cortisol concentrations were elevated at 0.5 h postsedation among fish sedated with eugenol and MS‐222, whereas cortisol levels of electrosedated fish were comparatively low and stable throughout the experiment. Conversely, plasma glucose and lactate levels increased markedly from 0.5 to 2 h postsedation among electrosedated fish, whereas the responses among fish treated with eugenol or MS‐222 were weak or negligible. Our results indicate that electrosedation, benzocaine, eugenol, and MS‐222 are all effective in quickly sedating largemouth bass. Physiological and behavioral data suggest that largemouth bass generally recover within 6 h of sedation using MS‐222, eugenol, or electrosedation.

The lack of an immediate‐release sedative (i.e., one for which no postsedation holding or withdrawal period is required) jeopardizes fish and fisheries research and poses considerable risk to those involved in aquatic resource management and the operation of public hatcheries and commercial fish farms. Carbon dioxide may be used as an immediate‐release sedative, but it is slow‐acting and difficult to apply uniformly and effectively. Tricaine methanesulfonate (MS‐222) is easier to apply but requires a 21‐d withdrawal period. The lack of an immediate‐release sedative approved by the U.S. Food and Drug Administration (FDA) is a consequence of numerous factors, including the complexities of the approval process, the substantial human and monetary resources involved, and the specialized nature of the work. Efforts are currently underway to demonstrate the safety and effectiveness of benzocaine‐ and eugenol‐based products as immediate‐release sedatives. However, pursuing approvals within the current framework will consume an exorbitant amount of public and private resources and will take years to complete, even though both compounds are “generally recognized as safe” for certain applications by the FDA. We recommend using risk management–based approaches to increase the efficiency of the drug approval process and the availability of safe and effective drugs, including immediate‐release sedatives, for use in the fisheries and aquaculture disciplines.

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 (CO2; ∼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 (CO2 [z] > benzocaine [y] > eugenol [y] > MS‐222 [y] > electrosedation [x]), recovery of equilibrium (CO2 [z] > eugenol [z] > MS‐222 [y] > benzocaine [y] > electrosedation [x]), and responsiveness to tactile stimulus (eugenol [z] > MS‐222 [y] > benzocaine [y] > CO2 [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 (CO2 [z] > eugenol [y] > benzocaine [x] > MS‐222 [x] > electrosedation [w]), with cumulative means ± SEs of 5.9 ± 0.2 min for CO2, 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, CO2 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

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