Abstract

Euthanasia of goldfish using MS-222 overdose via immersion is insufficient, highlighting the need for alternative techniques.¹ This study investigated the effectiveness of potassium chloride (KCl) to euthanize anesthetized koi (Cyprinus carpio). Twenty-eight healthy koi were anesthetized via immersion in buffered tricaine methanesulfonate (MS-222) 500 mg/L for 10–12 minutes, manually removed to room air, and randomly administered 10 mEq/kg KCl (333 mg/mL) via one of three routes: intracardiac injection (IC) (n=7), intracoelomic injection (ICe) (n=7), topical splash over the gill filaments bilaterally (T) (n=7), or control (C) (n=7). A Doppler crystal was placed over the heart and sounds were assessed continuously from immediately prior to treatment until 5 minutes post-treatment and every 5 minutes thereafter until Doppler sound cessation, resumption of operculation, or 30 minutes. Time to Doppler sound cessation or resumption of operculation was recorded. Doppler sound cessation occurred in 7/7 fish in IC (median 0.08, range 0–2.75 minutes), 1/7 fish in T (11 minutes), 0/7 fish in ICe, and 0/7 fish in C. In T, 6/7 fish maintained Doppler sounds to 30 minutes. All fish in ICe (7/7) and C (7/7) resumed operculations with median (range) times of 22 (7–30) and 16 (9–29) minutes, respectively. Intracardiac KCl at 10 mEq/kg rapidly results in Doppler sound cessation and is a successful technique for euthanasia of anesthetized koi. Intracoelomic and topical KCl at 10 mEq/kg does not reliably produce euthanasia in koi. Koi resumed operculation following 10–12 minutes of immersion in MS-222 at 500 mg/L.

Acknowledgments

The authors wish to thank Kent Passingham, Taylor Gregory, Taylor Locklear, and Ashley Souza for their technical assistance.

* Presenting author

Literature Cited

1.  Balko JA, Oda A, Posner LP. 2018. Use of tricaine methanesulfonate or propofol for immersion euthanasia of goldfish (Carassius auratus). J Am Vet Med Assoc. 52(12);1555–1561.