Use of electronarcosis to immobilize juvenile and adult northern pike
Electronarcosis, the immobilization of a fish after an electric current has been applied and discontinued, is a potential alternative to chemical anesthetics. Successful narcosis was defined as the immobilization of a fish for 1–15 min without causing physical damage. In the laboratory, AC successfully narcotized juvenile (13–19‐cm standard length, SL) northern pike ( Esox lucius ) at selected voltages; however, AC voltages that produced narcosis or resulted in physical damage were variable and unpredictable. In contrast, 60–90‐V pulsed DC (PDC) for 10–60 s successfully narcotized juvenile pike without inducing physical damage. Duration of narcosis was directly related to voltage and inversely related to fish length. In the hatchery, sexually mature northern pike (45–97 cm SL), collected from the Mississippi River, were successfully narcotized by 60‐V PDC for 10 s. Duration of narcosis was unrelated to fish length or sex, and averaged 58 ± 7 s (mean ± SE). This allowed sufficient time to collect eggs or milt. All fish were swimming upright within 3 min after treatment, and no mortalities were observed over the next 24 h. Survival of eggs from fertilization to eye‐up did not significantly differ between eggs collected from electronarcotized adults and adults anesthetized with MS‐222 (tricaine methanesulfonate). Electronarcosis represents a possible alternative to chemical anesthetics for immobilizing northern pike broodstock without an apparent impact on egg survival.