Current AVMA euthanasia guidelines for finfish recommend "immersion in...MS-222 [at] 250 to 500 mg/L...for 10 minutes following loss of rhythmic opercular movement...."1 Pilot research conducted in goldfish questioned this recommendation. Goals of this study include: (1) substantiate current euthanasia guidelines using MS-222 in goldfish, (2) determine if propofol immersion at five times the anesthetic dosage for 30 minutes is sufficient for euthanasia of goldfish, and (3) quantify the duration of forward blood flow following MS-222 overdose followed by decapitation in goldfish.
Twenty-four, healthy, adult goldfish were individually exposed to one of four treatments: MS-222 at 500 mg/L for 15 minutes (M15), MS-222 at 500 mg/L for 30 minutes (M30), propofol at 25 mg/L for 30 minutes (P30), or MS-222 at 500 mg/L for 15 minutes followed by decapitation (M15D). Time to anesthetic induction and cessation of operculation were recorded. Following the prescribed exposure, each fish was placed in anesthetic-free water (M15, M30, P30) or decapitated and positioned in lateral recumbency out of water (M15D). Forward flow of blood (Doppler) and associated heart rate were recorded every five minutes until cessation of sound or resumption of operculation. Time to resumption of operculation and recovery were recorded. Recovered fish were monitored for latent morbidity or mortality.
Overall survival in M15, M30, and P30 groups was 5/6, 6/6, and 5/6 fish, respectively. Median induction time in M15, M30, and P30 groups was 1.35 (0.75–1.45), 1.52 (1.05–1.73), and 1.60 (0.92–1.92) minutes, respectively. Following freshwater placement, median time for resumption of operculation in M15, M30, and P30 groups was 6.52 (2.08–15.25), 0.96 (0.43–8.50), and 0.42 (0.30–14.00) minutes and recovery was 24.13 (4.37–32.45), 41.33 (21.00–87.22), and 54.25 (20.25–331.00) minutes, respectively. Median time to loss of Doppler sounds in the M15D group was 78 (30–240) minutes and 248 minutes and 780 minutes in the non-survivors in the M15 and P30 groups, respectively. No latent morbidity or mortality was noted.
Thirty minutes of immersion in MS-222 at 500 mg/L or propofol at 25 mg/L are not reliable methods of euthanasia in goldfish. Prolonged cessation of operculation is not associated with death in goldfish.
* Presenting author
+ Student presenter
1. AVMA Panel on Euthanasia. AVMA Guidelines for the Euthanasia of Animals: 2013 Edition. American Veterinary Medical Association; 2013 [accessed 2016 Jan 7]. www.avma.org/KB/Policies/Documents/euthanasia.pdf.