Efficacy and Physiological Responses of Grass Carp to Different Sedation Techniques: I. Effects of Various Chemicals on Sedation and Blood Chemistry

Abstract Grass carp Ctenopharyngodon idella are commonly used as a low cost, biological control for aquatic vegetation in aquaculture ponds and other private and public waters. In order to minimize the risk of establishing self‐sustaining populations in U.S. waters, many states now require grass carp be certified as triploid prior to sale and stocking. To facilitate ploidy testing, grass carp are typically sedated before collecting blood samples. Chemical sedatives such as tricaine methanesulfonate (MS‐222) and carbon dioxide (CO 2 ) are most commonly used to sedate fish, but there is increasing interest in other chemical sedatives such as benzocaine and eugenol. We evaluated time to induction to Stage IV sedation and recovery, survival, and postsedation blood chemistry of grass carp (301 ± 8 g, mean ± SE) sedated with MS‐222 (150 mg/L), benzocaine (150 mg/L), eugenol (60 mg/L), or CO 2 (∼400 mg/L). Induction times for all sedatives excluding CO 2 (14.9 min) were less than 2.4 min (range, 1.5–2.4 min). Average recovery time after induction was 5.8 min (range, 2.8–8.3 min) excluding benzocaine, which had a recovery time of 15.4 min. Survival was high and unaffected by sedative option. Plasma cortisol and lactate levels peaked between 0.5 and 1 h postinduction before returning to resting levels at 6 h postinduction. No obvious changes were observed in blood glucose or hematocrit. Each of the sedatives was effective in sedating grass carp, and though changes in blood chemistry indicated that an acute stress response occurred, the response was transient. Although each of the evaluated sedatives would facilitate ploidy testing, some strategies may be more appropriate than others based on FDA approval status and access to the sedative compound, handling time, withdrawal period, and on‐site conditions and resources.