Abstract

Doses of buffered MS222 up to 1000 mg/L for 15 minutes are reported inefficient to produce euthanasia in goldfish.¹ The goal of this study was to determine if goldfish can be euthanized by prolonged immersion in MS222. Goldfish (n=24, weight: 1–10 grams) were assigned to 4 groups. After acclimation including standard quarantine treatments, physical examinations were unremarkable. Fish were kept in 32-L tanks equipped with filters. The first group (G1) was exposed to 500 mg/L of buffered MS222 for 15 minutes then placed into freshwater for 3 hours. The second (G2) and third groups (G3) were exposed to 1000 mg/L of buffered MS222 for 15 minutes then placed into freshwater for 3 hours and 18 hours, respectively. The fourth group (G4) was exposed to 1000 mg/L of buffered MS222 for 60 minutes then placed into freshwater for 3 hours. Time of cessation and return of operculation were recorded at each concentration. If the goldfish did not resume operculation at the end of the observation period, heart rate was evaluated with a doppler. If heartbeat was detected, pithing followed by histopathology was performed. Median time of cessation of operculation was 35 seconds at 1000 mg/L, and 65 seconds at 500 mg/L. Re-operculation occurred only in G1 in 5 out of 6 individuals. All fish from G1, 4 fish from G2, 0 fish from G3, 1 fish from G4 had remaining heartbeats. Necropsy results were unremarkable. Overall, a dose of 1000 mg/L of buffered MS222 for 15 minutes was efficient to euthanize goldfish.

Acknowledgments

The authors wish to thank the team of the Clinique des Animaux Exotiques for their technical support.

*Presenting author

Literature Cited

1.  Balko J, Oda A, Posner LP. 2018. Use of tricaine methanesulfonate or propofol for immersion euthanasia of goldfish (Carassius auratus). J Am Vet Med Assoc. 252: 1555–1561.