Fish are commonly sedated to render them immobile and thus easier to handle for research, veterinary, and aquaculture practices. Since sedation itself imposes a significant challenge on the targeted fish, the selection of sedation methods that minimize physiological and behavioral disturbance and recovery time is essential. Two popular sedation methods include the chemical tricaine methanesulfonate (MS-222) and electrosedation. Although many studies have already investigated the physiological consequences of these methods, there is limited research examining the latent behavioral effects on fish. Using Largemouth Bass Micropterus salmoides as a model species, we compared the postsedation behaviors of fish that were sedated with either MS-222 or electrosedation to those of a control group exposed to the same handling protocol. Immediately after sedation, fish exposed to either treatment demonstrated lower reflex scores than the control group. Time to resume regular ventilation did not differ between chemically sedated and electrosedated fish; however, electrosedated fish regained equilibrium faster (mean ± SE = 154 ± 20 s) than fish that were exposed to MS-222 (264 ± 30 s). Locomotor activity and swimming performance were assessed at 5-, 30-, or 60-min intervals, beginning after individuals had recovered from sedation sufficiently to regain equilibrium. For all postsedation intervals, locomotor activity was two times greater in the electrosedated group than in the control and MS-222 groups. Other behavioral measures (refuge emergence time, activity level, and flight initiation distance) and swimming performance did not differ at 5, 30, or 60 min postrecovery for any of the treatment groups. Our results indicate that while both chemical and electrical sedation methods result in impairment (i.e., sedation) immediately after treatment, these behavioral effects do not persist beyond 5 min postrecovery, and the two methods have similar impacts on Largemouth Bass. However, we caution that these results cannot be extrapolated to other fish species without further study.

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Journal Transactions of the American Fisheries Society
Prystay, T.S. (Tanya S.), Elvidge, C.K. (Chris K.), Twardek, W.M. (William M.), Logan, J.M. (James M.), Reid, C.H. (Connor H.), Clarke, S.H. (Shannon H.), … Cooke, S.J. (2017). Comparison of the behavioral consequences and recovery patterns of largemouth bass exposed to MS-222 or electrosedation. Transactions of the American Fisheries Society, 146(3), 556–566. doi:10.1080/00028487.2017.1285354