Etomidate as an Effective Alternative Method of Euthanizing Adult Zebrafish (Danio Rerio)

Abstract

We assessed the efficacy of etomidate in euthanizing adult zebrafish. The aims of this study were to investigate: 1) the efficacy of 2 concentrations and 2) the effects at 2 densities. Aim 1-Fish (n=10 fish/group) were immersed in either 6 mg/L (Eto-6) or 10 mg/L (Eto-10) etomidate. Aim 2- either 5 or 10 fish were immersed in Eto-6. Tanks were video recorded and scored by two blinded observers. The parameters monitored included: 1) loss of righting reflex (LORR); 2) undulation cessation; 3) cessation of operculation (COO); and 4) loss of startle reflex. After the 30 minute immersion, fish were transferred to recovery tanks and monitored once every 5 minutes for 60 minutes. Results - Aim 1, the time to undulation cessation, COO, and loss of startle reflex was significantly shorter in the Eto-10 group and there was no difference in LORR. Aim 2, the time to LORR and undulation cessation was significantly shorter in the 5 fish/L group and there was no significant difference in time to COO or loss of startle reflex. No aversive behaviors were noted and fish in all groups were effectively euthanized by 30 minutes. This study indicates that Eto-6 or Eto-10 effectively euthanizes adult zebrafish.