Abstract

Intracardiac potassium chloride (KCl) at 10 mEq/kg is effective for euthanasia of anesthetized koi (Cyprinus carpio).¹ Objectives for this study included investigation of KCl immersion and intracardiac KCl dosing <10 mEq/kg for euthanasia of anesthetized koi. Twenty-eight koi were immersed in buffered tricaine methanesulfonate at 150 mg/L until loss of the righting reflex was observed and randomly administered one of five treatments: intracardiac KCl at 2.5 (IC2.5) or 5 mEq/kg (IC5) (n=6/group), immersion in KCl at 100 (IMS100) or 4500 mEq/L (IMS4500) (n=5/group), or captive bolt (CB) (n=5). Serial heart rate assessments via Doppler device were performed until Doppler sound cessation, recovery, or 90 minutes. Tail vein venipuncture for plasma potassium quantification was performed prior to treatment (P1) and at the time of Doppler sound cessation (P2) in IMS4500 and CB. Data were compared between groups (significance p<0.05). Doppler sound cessation occurred in 6/6, 6/6, 0/5, 0/5, and 5/5 fish in IC2.5, IC5, IMS100, IMS4500, and CB, respectively, with median (range) times of 1.7 (0–17.2), 1.0 (0–20.3), and 440.0 (225.0–510.0) minutes in IC2.5, IC5.0, and CB, respectively (p=0.0017). Doppler sounds persisted for 90 minutes for all koi in IMS4500. All koi in IMS100 recovered in <90 minutes. Median (range) P1 and P2 values for IMS4500 was 2.5 (2.4–3.0) and 23.6 (19.8–73.6) and CB was 3.4 (3.1–3.8) and 7.3 (5.7–8.8) mmol/L, respectively. Intracardiac KCl at 2.5 and 5 mEq/L is effective for euthanasia of anesthetized koi. Despite significant hyperkalemia, immersion in KCl did not cause myocardial arrest.

Acknowledgements

The authors wish to thank Craig Harms, Lysa Posner, Greg Lewbart, Maria Serrano, and Lynnette McCall for study assistance.

*Presenting author

Literature Cited

1.  Louis MM, Houck EL, Lewbart GA, Posner LP, Balko JA. 2020. Evaluation of potassium chloride administered via three routes for euthanasia of anesthetized koi (Cyprinus carpio). J Zoo Wildl Med 51(3):485–9.