Doses of buffered tricaine methanesulfonate (MS-222) up to 1000 mg/L for 15 minutes are reported inefficient to produce euthanasia in goldfish. The goal of this study was to determine if goldfish can be euthanized by more prolonged immersion in MS-222.
24 healthy goldfish (weight range: 1 to 10 g) were randomly assigned to 4 groups of 6 fish.
The first group (G1) was exposed to 500 mg/L buffered MS-222 for 15 minutes then placed in freshwater for 3 hours. The second (G2) and third groups (G3) were exposed to 1000 mg/L of buffered MS-222 for 15 minutes then placed in freshwater for 3 hours and 18 hours respectively. The fourth group (G4) was exposed to 1000 mg/L of buffered MS-222 for 60 minutes then placed in freshwater for 3 hours. Time to cessation and return of operculation were recorded. If the goldfish did not resume operculation, heart rate was evaluated by Doppler ultrasonic flow detector.
Median times to apnea were 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, 3 fish from G2, 0 fish from G3, 1 fish from G4 had remaining heartbeats at the end of the observation period.
Overall, a dose of 1000 mg/L of buffered MS-222 for 15 minutes was efficient to euthanize juvenile goldfish at 20 °C. Different fish body mass and water quality parameters might explain different results compared to previous studies.