Cardiac and behavioral responses to chemical and electrical immobilization in Lake Trout

Objective

Immobilizing or anesthetizing fish is important for promoting fish welfare in numerous routine activities that involve handling. Electroanesthesia, an alternative to traditional chemical anesthetics, uses weak electrical current to immobilize fish while current is applied, resulting in near-immediate induction and recovery. The physiological effects of electroanesthesia appear to be minimal or comparable to those of chemical anesthetics, but knowledge gaps exist on cardiac responses during treatment and behavioral responses in a controlled setting.

Methods

Lake Trout Salvelinus namaycush were immobilized by one of four treatments: control (physical restraint); eugenol (AQUI-S 20E); and continuously applied, low-voltage electroanesthesia with either constant DC or transcutaneous electrical nerve stimulation (TENS). We evaluated the heart rate while fish were immobilized, reflexes at 1 h posttreatment, and survival and movements in a laboratory setting over a 6-d posttreatment period.

Results

The heart rates of fish immobilized with either electroanesthesia treatment (constant DC: mean ± SE = 12.6 ± 1.1 beats/min; TENS: 13.1 ± 1.2 beats/min) were not significantly different from those of control fish (10.0 ± 1.2 beats/min) while immobilized. However, fish immobilized with eugenol exhibited heart rates that were more than three times higher (32.1 ± 1.2 beats/min) than those of control fish while immobilized. Treatments had no effect on reflex scores at 1 h posttreatment, the 6-d survival rate of fish (100%), or movement behavior during the hours (1–24 h) or days (6 d) after treatment.

Conclusions

This study adds to a growing body of research finding a lack of negative physiological or behavioral responses resulting from continuously applied electroanesthesia, suggesting that it is at least as safe as many chemical anesthetics in this respect. The significant cardiac response of Lake Trout while immobilized with eugenol warrants further investigation. While the body of research on immobilizing agents in fish grows, species-specific data remain sparse, and users would benefit from pilot testing before wider application.