Induction, Recovery, and Hematological Responses of Largemouth Bass to Chemo- and Electrosedation

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.