Investigation of Potassium Chloride for Euthanasia of Anesthetized Marine Toads (Rhinella marina)

Abstract

Abstract Euthanasia techniques in amphibians are poorly described and sparsely validated. This study investigated potassium chloride (KCl) for euthanasia of anesthetized marine toads (Rhinella marina). Twenty-three toads were immersed in buffered MS-222 (2 g/L) for 5 min beyond loss of righting reflex, manually removed, and randomly administered KCl (n = 6/group) via one of three routes: intracardiac at 10 mEq/kg (IC), intracoelomic at 100 mEq/kg (ICe), or immersion at 4,500 mEq/L (IMS) or no treatment (C) (n = 5/group). Doppler sounds were assessed continuously from prior to treatment until 5 min posttreatment and every 5 min thereafter until sound cessation or resumption of spontaneous movement. Plasma potassium concentration (K+) was measured at the time of Doppler sound cessation in ICe and IMS. In IC, ICe, IMS, and C, Doppler sound cessation occurred in 4/6, 6/6, 6/6, and 1/5 toads with median (range) or mean ± SD times of 0.23 (0–4.65), 17.5 ± 9.0, 40.6 ± 10.9, and >420 min, respectively. Nonsuccess in 2/6 toads in IC was suspected due to technique failure. Plasma K+ exceeded the limits of detection (>9 mmol/L) in 12/12 toads in ICe and IMS. Five of six toads in C resumed spontaneous movement at median (range) times of 327 (300–367) min. KCl delivered via an intracardiac, intracoelomic, or immersion route resulted in Doppler sound cessation in 16 of 18 toads and may be appropriate for euthanasia of anesthetized marine toads.