Efficacy and Physiological Responses of Grass Carp to Different Sedation Techniques: II. Effect of Pulsed DC Electricity Voltage and Exposure Time on Sedation and Blood Chemistry

Owing to the current absence of an approved “immediate‐release” chemical sedative for use on fish, researchers have been exploring alternative methods that would allow treated fish to be released immediately after sedation, including the use of electrosedation. To address the efficacy of this approach, we evaluated induction and recovery times, survival, and postsedation hematology of grass carp Ctenopharyngodon idella (291 ± 6.7 g, 30.6 ± 0.3 cm TL, mean ± SE) sedated by exposure to 100, 150, or 200 V of pulsed DC (30 Hz and 25% duty cycle) for 5 or 10 s. Regardless of voltage strength or exposure time, all fish were sedated to Stage IV sedation within 0.75 min and recovered within 1.5 min. Although recovery times for fish exposed to electrosedation for 10 s were longer than those for fish electrosedated for 5 s using 100 and 150 V, the opposite trend was observed among fish sedated using 200 V. Overall, induction and recovery times were short: total time elapsed from induction to full recovery ranged from 1.0 to 2.1 min (mean, 1.6 min). No mortalities were observed 24 h postsedation. Hematological changes observed were consistent with an acute stress response, but these effects were transient and few differences were observed among the electrosedation protocols used. Our results indicate that pulsed DC electrosedation is an effective strategy for quickly and easily sedating grass carp.