Comparison of Tricaine Methanesulfonate (MS-222) and Alfaxalone Anesthesia in Bluegill Fish (Lepomis macrochirus)

Bluegill fish ( Lepomis macrochirus ) are a popular sportfish across North America. Research involving bluegill has focused mainly on locomotion, environmental monitoring, bioaccumulation, and toxicology. With fish becoming more popular research models, bluegill use may increase. Consideration for sedation and anesthesia in bluegill is lacking. MS-222 is a commonly used anesthetic in fish that requires a 21-d washout period before entry into the food chain. Other, safer options for anesthesia should be available. In this study, we first determined a suitable MS-222 dose for general anesthesia, then compared it with 2 different concentrations of alfaxalone (5 and 10 mg/L). Both concentrations of alfaxalone were adequate to reach the desired anesthetic plane, although time to effect was dose-dependent and longer in these groups when compared with MS-222. Time to recovery was also prolonged in both alfaxalone groups compared with the MS-222 group. We also assessed anesthetic degradation in the water bath over time. In this study, we show that sedation with alfaxalone at 5 and 10 mg/L is just as effective as MS-222 with no degradation of either anesthetic over the time measured.