Summary
Commercially available electrosedation apparatuses (e.g., the Smith‐Root Portable Electroanesthesia System [PES]) are growing in popularity within the fisheries research community. This technology can be used to immobilize fish rapidly and does not require a withdrawal period before fish are released. A number of studies examined how various settings (e.g., duration, frequency, voltage) influence the performance of the PES for fish sedation, but comparatively less is known about the role of fish orientation and position on the efficacy of electrosedation within the PES. We compared recovery times of Bluegill Lepomis macrochirus upon manipulation of three variables: orientation of fish, electric field size (i.e., spacing between the anode and cathode), and fish proximity relative to the anode. Fish were individually exposed to pulsed DC with a standardized frequency (100 Hz), voltage (90 V), and shock duration (3 s). Full recovery time was significantly longer for fish oriented at horizontal angles (0° and 180°) than at acute angles (45° and 135°). Significant interactions were found between orientation and electrode spacing, as well as between orientation and fish proximity. These findings are pertinent to researchers in the field looking to optimize recovery time for a quick release after surgery, tagging, or any other time fish sedation is required.
Methodology
Prior to the experiments, a nonconductive frame was constructed to support a fine‐mesh net to hold the fish in a fixed position (Hudson et al. 2011; Figure 1a). The frame was constructed using chlorinated PVC (CPVC) 1.3‐cm piping, electrical tape, and magic wrap. A net pocket (made from plastic insect window screen) was used to restrain the fish. The netting consisted of a 27.9‐cm × 27.9‐cm net bag with two lengths of CPVC 1.3‐cm‐diameter pipe, 55.9 cm long, fitted through the top and a fiberglass rod at the bottom of the bag to keep the net structured and weighted. The fish placement section of the netted bag was small enough to prevent lateral movement of the fish during trials.
Prior to the experiments, a nonconductive frame was constructed to support a fine‐mesh net to hold the fish in a fixed position (Hudson et al. 2011; Figure 1a). The frame was constructed using chlorinated PVC (CPVC) 1.3‐cm piping, electrical tape, and magic wrap. A net pocket (made from plastic insect window screen) was used to restrain the fish. The netting consisted of a 27.9‐cm × 27.9‐cm net bag with two lengths of CPVC 1.3‐cm‐diameter pipe, 55.9 cm long, fitted through the top and a fiberglass rod at the bottom of the bag to keep the net structured and weighted. The fish placement section of the netted bag was small enough to prevent lateral movement of the fish during trials.