Evaluating immobilisation thresholds and suitability of conductive glove electrodes for largemouth bass electroanaesthesia

Abstract

Although electroanaesthesia (immobilising fish with weak currents and direct electrode contact for short-term handling and surgeries) is becoming more common, detailed data on electroanaesthesia immobilisation thresholds and potential morphological predictors of such thresholds remain sparse. We administered electroanaesthesia to largemouth bass (Micropterus nigricans) over a large range of body sizes using conductive mesh gloves connected to a power supply with fine-scale current control and real-time output display, noting current strengths at which tetany occurred. We also investigated whether a range of morphological indices were correlated with the currents required to induce tetany as a proxy for electroanaesthesia. Larger fish required stronger currents before tetany was observed, and larger fish were also more likely to fail to reach tetany before the maximum output on the apparatus (30 V) was reached, a finding that was slightly offset by increasing condition factor. Body length was a suitable predictor of the current required to induce tetany; no other morphometric indices examined were superior to length in this regard. However, there was very high variability in current strengths required to induce electroanaesthesia, likely attributable to consistency challenges associated with the use of conductive mesh gloves as electrodes (e.g., location of contact, wear-and-tear on gloves). We explore the implications of our results for applications of electroanaesthesia in the field, and make recommendations for the development and implementation of novel technologies and best practices when using electroanaesthesia on fish.