Effects of chemical anesthesia versus electro-immobilization for acoustically tagging juvenile hybrid Striped Bass

ABSTRACT Objective Acoustic telemetry is a tool to track fish movements, behavior, and mortality; however, tagging can be stressful for fish. Electro-immobilization is one of the few available options to immediately release tagged fish in the wild. We compared the use of electroanesthesia and the traditionally popular chemical anesthetic MS-222 with respect to their influence on recovery, growth, and survival in juvenile hybrid Striped Bass (White Bass Morone chrysops × Striped Bass M. saxatilis). Methods We randomly assigned 150 hybrid Striped Bass (187–245 mm) to a control or one of four treatments: electroanesthesia tagging, electroanesthesia sham (surgery but no tag), MS-222 tagging, or MS-222 sham. After surgery, we monitored fish recovery time, wound healing, growth, survival, and tag retention for 74 d after anesthesia. Results Induction and recovery times were lower in the electroanesthesia than in the MS-222 treatments. Wound healing and tag retention were similar across treatments and time; after 74 d, all incision sites were at least partially closed, 31% of the fish had complete incision closure, 95% of the fish had incision redness or inflammation, and 68% of fish had the suture present. Hybrid Striped Bass from both tagging treatments had slower growth 36 d posttagging than the control fish but lost less weight over the last 38 d when water temperatures were <6.9°C. Nine fish in each tagging treatment and five fish in each sham treatment and the control died, but survival was similar among the treatments (mean = 78%). Conclusions Our results indicate that MS-222 and electroanesthesia have little detectable effect on healing, growth, and survival in juvenile hybrid Striped Bass, but induction and recovery times are reduced with electroanesthesia. Thus, electroanesthesia represents a viable option for acoustically tagging juvenile hybrid Striped Bass and potentially other fishes. However, handling and acoustically tagging juvenile hybrid Striped Bass should be performed with caution due to the potential for short-term growth effects and delayed mortality.