Abstract

Giant Pacific octopuses (Enteroctopus dofleini) (GPOs) are popular aquarium inhabitants and research animals. Evidence-based data on best practices for GPO anesthesia techniques are lacking. Unpublished data from a GPO veterinary care survey indicate that magnesium chloride (MgCl₂) and isoflurane may be promising. Pilot study objectives were to evaluate and characterize the anesthetic efficacy of MgCl₂ and isoflurane in GPOs. Five juvenile GPOs (0.3–8.9 kg) were immersed in escalating concentrations of MgCl₂ (15–40 g/L) or bubbled isoflurane in 100% oxygen (0.5–3%) in 50–75 L seawater (3.5–11°C) until either sedative effects or 60 minutes. Serial monitoring of sedation (muscle tone, sucker adhesion, mentation), ventilation, color, and water quality was performed. In sedated GPOs, basic diagnostics (physical examination, ultrasonography, needle puncture) were attempted. Seven MgCl2 and four isoflurane trials were completed with total exposure times of 41–102 minutes. Adequate sedation was not achieved with MgCl₂ 15 g/L (n=1), MgCl₂ 35 g/L (n=1), or isoflurane 0.5–3% (n=4). One GPO exposed to isoflurane 3% became minimally responsive (suspected deep anesthesia) with marked hypoventilation; as a result of this complication, isoflurane trials were discontinued. MgCl₂ 25 g/L (n=1) prevented response to basic diagnostics and decreased muscle tone and sucker adhesion but resulted in pale color and a prolonged recovery (138 minutes). MgCl₂ 40 g/L produced sedation sufficient for physical examination in one of four exposed GPOs. While MgCl₂ may provide sedation or anesthesia in GPO, magnitude of effects are variable and prolonged recovery may result. Isoflurane should be used with caution in GPO.