Abstract

Immersion overdose in tricaine methanesulfonate (MS-222) is ineffective for goldfish euthanasia.¹ This study investigated potassium chloride (KCl) via four routes for goldfish euthanasia. Thirty clinically healthy goldfish were anesthetized via immersion in buffered MS-222 (300 mg/L) and randomly administered one of five treatments: KCl (330 mg/mL) via intracardiac injection at 10 mEq/kg (IC), intracoelomic injection (ICe) or bilateral topical delivery over the gill filaments (T) at 100 mEq/kg, 90-minute immersion at 4500 mEq/L dissolved in induction solution (W), or no treatment (X). Following treatment, all fish were moved to anesthetic-free freshwater. Serial heart rates were collected via Doppler device until sound cessation or recovery. Median (range) time to perform treatments was 315 (73–480), 3 (3–3), and 10 (10–10) seconds in IC, ICe, and T, respectively. Doppler cessation occurred in 6/6, 6/6, 6/6, 6/6, and 0/6 fish in median (range) times of 3 (0–210), 18 (10–45), 118 (90–390), and 150 (60–240) minutes, in IC, ICe, T, W, and X, respectively. Following treatment, 1/6, 2/6, 6/6, and 4/6 fish in IC, ICe, T, and W, respectively, exhibited intermittent brief jerking movements. Median (range) time to recovery in X was 5.5 (3.5–6.5) minutes. All administration routes were effective, but time to Doppler cessation varied and transient movements were noted. Preliminary follow-up research revealed that return to MS-222 following treatment abolished movements. Intracoelomic KCl at 100 mEq/kg was technically simple and produced a rapid, consistent time to Doppler sound cessation in 6/6 anesthetized goldfish. Return to MS-222 following KCl administration may be warranted.

Acknowledgements

The authors wish to thank Dr. Emily Christiansen, Dr. Craig Harms, Emily Schlake, Stephen Santangelo, and NCSU CVM Laboratory Animal Resources for project support.

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 252(12): 1555–1561.